Alan E. Lichtin, MD

A breakthrough in understanding the pathogenesis of thrombotic thrombocytopenic purpura (TTP) came with the discovery of ADAMTS13 (an abbreviation for “a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13”), a plasma protein that cleaves von Willebrand factor, which interacts with platelets to promote blood clotting. If ADAMTS13 is lacking, unusually large multimers of von Willebrand factor can accumulate and trigger intravascular platelet aggregation and microthrombosis, causing the signs and symptoms of TTP.^1–3

This knowledge has practical applications: we can now measure ADAMTS13 activity, ADAMTS13 inhibitor, and antibodies against ADAMTS13 to help us diagnose TTP and distinguish it from other forms of thrombotic microangiopathy, such as hemolytic-uremic syndrome, that have similar symptoms but require different treatment.

Using case studies, this article describes typical presentations of acute and relapsing TTP; the role of laboratory testing, including the ADAMTS13 assay; how to distinguish TTP from other conditions that present similarly; and how to manage this condition.

A HIGH RISK OF DEATH WITHOUT PLASMA EXCHANGE

TTP is characterized by disseminated microthrombi composed of agglutinated platelets and von Willebrand factor in small vessels. Tissue damage by microthrombi can cause thrombocytopenia (platelet deficiency), microangiopathic hemolytic anemia (loss of red blood cells caused by destructive conditions in small vessels), and multiorgan failure.¹

Untreated TTP has a mortality rate of about 90%.¹ As shown in Case 1, Case 2, and Table 1, rapid diagnosis and prompt initiation of daily therapeutic plasma exchange can improve this grave outlook.⁴

ADAMTS13 DEFICIENCY CAN BE ACQUIRED OR CONGENITAL

Two major forms of TTP with ADAMTS13 deficiency and microvascular thrombosis are recognized:

Acquired TTP, the more common form, peaks in incidence between ages 30 and 50.^2,5 It more often affects women, particularly during and after pregnancy (its estimated prevalence is 1 in 25,000 pregnancies), and African Americans.⁶ Acquired TTP may be:

• Primary (idiopathic or autoantibody-mediated), associated with severely decreased ADAMTS13 and the presence of ultra-large von Willebrand factor multimers, or
• Secondary (23%–67% of cases), arising from a variety of conditions, including autoimmune disorders (eg, systemic lupus erythematosus, rheumatoid arthritis), solid organ or hematopoietic cell transplant, malignancy, drugs, and pregnancy (Table 2).^1,5–8 Secondary TTP has a worse prognosis than idiopathic TTP.^5,9

Congenital TTP (Upshaw-Shulman syndrome) is a rare autosomal-recessive disease caused by compound heterozygous or homozygous mutations of the ADAMTS13 gene, producing nonfunctional ADAMTS13 protein. Patients have severely deficient ADAMTS13 activity but usually do not develop autoantibodies. There is a high risk of chronic, relapsing episodes; identified triggers include pregnancy and heavy alcohol intake.^2,10 About half of patients with congenital TTP have an early onset, usually presenting with acute TTP between birth and age 5, and about half have a late onset, usually remaining without symptoms until age 20 to 40.

THE CLINICAL PICTURE OF TTP IS NOT ALWAYS CLASSIC

TTP is primarily diagnosed clinically, but diagnosis is often difficult because of various nonspecific symptoms. Typical TTP presents with the “classic pentad”:

• Severe thrombocytopenia (70%–100% of patients)
• Microangiopathic hemolytic anemia with multiple schistocytes (70%–100%) (Figure 1)
• Neurologic involvement (50%–90%)
• Renal abnormalities (about 50%)
• Fever (25%).

However, the entire picture often does not emerge in a single patient.^2,6 Waiting for the entire pentad to develop before diagnosing TTP can have grave clinical consequences,^1,2,5 and the presence of thrombocytopenia and unexplained microangiopathic hemolytic anemia are considered clinically sufficient to suspect TTP.⁵

Neurologic symptoms usually fluctuate. They can include mild abnormalities such as weakness, dizziness, headache, blurred vision, ataxia, and transient mental status changes, as well as severe abnormalities including stroke, seizure, and coma.^2,6

Most patients have normal findings on computed tomography and magnetic resonance imaging at the onset of neurologic symptoms or with a history of TTP. Some patients (8%–39%) show reversible acute brain lesions, including ischemic changes.^11–13

Other signs and symptoms may result from multiorgan failure due to microthrombosis; ischemia in retinal, coronary, and abdominal circulations; and unconjugated hyperbilirubinemia.²

Atypical presentations. About 18% of patients have cardiac involvement from microvascular occlusion, with arrhythmia, angina, or congestive heart failure. Abdominal pain and pancreatitis occur in 5% to 13%, and visual disturbances in 8% to 10%.

Patients with an atypical presentation may not have laboratory evidence of microangiopathic hemolytic anemia, but an ADAMTS13 assay will show severely decreased activity. Therapeutic plasma exchange can improve atypical symptoms.^2,3,10,14,15

ADAMTS13 ASSAY IS KEY TO DIAGNOSIS

Laboratory evidence typically includes hemolytic anemia (reticulocytosis, schistocytes, elevated indirect bilirubin, reduced haptoglobin, elevated lactate dehydrogenase) and thrombocytopenia.³ There are no significant abnormalities in prothrombin time, international normalized ratio, activated partial thromboplastin time, fibrinogen, or D-dimer level.

Measuring the levels of ADAMTS13 activity, ADAMTS13 inhibitor, and ADAMTS13 antibody is becoming standard to confirm the diagnosis of TTP, to determine if it is congenital or acquired, and to distinguish it from thrombocytopenic conditions such as hemolytic-uremic syndrome, idiopathic thrombocytopenic purpura, and heparin-induced thrombocytopenia.^4,5 A newer ADAMTS13 assay based on fluorescence energy transfer (FRET) technology with a synthetic amino acid-von Willebrand factor peptide substrate has a faster turnaround time and less test variability.^6,16,17 This FRET assay can give the result of ADAMTS13 activity within 2 hours. In comparison, the assay based on multimeric von Willebrand factor takes 2 to 3 days, and mass spectrometry to measure the cleavage products of a synthetic von Willebrand factor molecule takes about 4 hours.^3,10,16

About two-thirds of patients with the clinical diagnosis of idiopathic TTP have ADAMTS13 activity levels lower than 10%.^5,14,18 In the appropriate clinical setting, this threshold level is highly sensitive (89%–100%) and specific (99%–100%) in differentiating TTP from other thrombotic angiopathies.^2,3,18

Note: The ADAMTS13 assay was needed for early correct diagnosis in Case 1 and Case 2.

Inhibitors provide more clues

Autoantibodies can be classified according to whether they inhibit ADAMTS13 activity.

Neutralizing inhibitors. Most cases of acquired, idiopathic TTP with severe ADAMTS13 deficiency are related to circulating autoantibodies that neutralize ADAMTS13 activity. This ADAMTS13 inhibitor level is obtained by measuring residual ADAMTS13 activity after mixing equal amounts of patient plasma with normal pooled plasma. ADAMTS13 inhibitor is detectable in 44% to 93% of patients with severely deficient ADAMTS13 activity.^3,6,19

Nonneutralizing inhibitors. From 10% to 15% of patients with TTP with severe ADAMTS13 deficiency lack ADAMTS13 autoantibodies measured by enzyme immunoassay but have nonneutralizing immunoglobulin G (IgG) or IgM autoantibodies. In such cases, ADAMTS13 deficiency may be related to increased antibody-mediated clearance or other unknown mechanisms.

Neutralizing inhibitors and nonneutralizing inhibitors may be present simultaneously in some patients.^3,10,19,20

Blood factors affect ADAMTS13 activity

Specimen factors can affect ADAMTS13 activity and antibody levels.

Hemoglobin is a potent inhibitor of ADAMTS13, so an elevated plasma level of free hemoglobin (> 2 g/dL) can reduce ADAMTS13 activity, as can hyperbilirubinemia (> 15 mg/dL).

High levels of endogenous von Willebrand factor, lipids, thrombin, or other proteases that may cleave ADAMTS13 can also reduce ADAMTS13 activity.³ Conversely, recent plasma exchange or transfusion can mask the diagnosis of TTP because of false normalization of ADAMTS13 activity. In addition, ADAMTS13 autoantibody can be detected in other immune-mediated disorders (eg, systemic lupus erythematosus, antiphospholipid syndrome), and hypergammaglobulinemia, as well as in 10% to 15% of healthy individuals.¹⁹

CONSIDER OTHER CONDITIONS

Before diagnosing TTP, other conditions causing thrombocytopenia and hemolytic anemia should be excluded by taking a careful clinical, laboratory, and medication history (Table 2). Of these conditions, the most challenging to differentiate from TTP—and often indistinguishable from it at presentation—is hemolytic-uremic syndrome (Table 3).

Hemolytic-uremic syndrome

Hemolytic-uremic syndrome presents with a triad of thrombocytopenia, acute renal failure, and microangiopathic hemolytic anemia, with increased lactate dehydrogenase levels. Renal dysfunction from ischemia or tissue injury by microvascular thrombi predominates. Hemolytic-uremic syndrome most often occurs in children and is often related to hemorrhagic enterocolitis caused by infection with Escherichia coli O157:H7 or Shigella species (90%–95% of cases).^1,2,5

From 5% to 10% of cases of hemolytic- uremic syndrome are atypical. These cases are not associated with diarrhea, and many are caused by genetic mutations that result in chronic excessive complement activation. Implicated genes regulate complement regulator factor H (20%–30% of cases) or CD46 (10%) and other cofactors, or autoantibodies against factor H (10%), which affect the alternate complement pathway.^6,21–23

Initial therapeutic plasma exchange is commonly undertaken for atypical hemolytic- uremic syndrome, particularly for patients at risk of rapid progression to end-stage renal failure. But despite such treatment, about 60% of these patients die or develop permanent renal damage within 1 year.^2,3,24

Eculizumab, a monoclonal antibody against complement component C5, has been approved by the US Food and Drug Administration for atypical hemolytic-uremic syndrome and may improve quality of life.^25–27

PLASMA EXCHANGE IS THE MAINSTAY OF THERAPY

In 2012, the British Society for Haematology published revised guidelines for managing TTP and other thrombotic microangiopathies.²⁸

Acquired idiopathic TTP with reduced ADAMTS13 activity requires immediate therapeutic plasma exchange. Daily plasma exchange combines plasmapheresis to remove circulating ultralarge von Willebrand factor-platelet strings and autoantibodies against ADAMTS13, and infusion of fresh-frozen plasma to replace ADAMTS13.¹⁸ This procedure is the mainstay of therapy and brings 70% to 90% of patients with idiopathic TTP to remission.^1,2,5,6 However, the optimal duration of daily plasma exchange and the number of procedures required is highly variable according to clinical condition. Therapeutic plasma exchange can also cause plasma-related adverse reactions.^9,28 Congenital TTP requires plasma infusion or exchange depending on the patient’s severity of ADAMTS13 deficiency.

Corticosteroids are used in combination with daily therapeutic plasma exchange, although evidence from controlled trials of their efficacy in this setting is lacking. Patients with severely decreased ADAMTS13 activity or low titers of ADAMTS13 autoantibodies tend to respond to the therapy.^5,8,29

An ADAMTS13 assay with a short turn-around time can help guide the decision to initiate therapeutic plasma exchange. However, if there is a strong clinical suspicion of TTP, plasma exchange should be initiated immediately without waiting for test results.^5,30 Monitoring ADAMTS13 activity or inhibitor during initial plasma exchange therapy has had conflicting results in several studies and is generally not recommended for patients with acquired TTP.^8,30,31

RELAPSE IS COMMON

About 20% to 50% of patients with idiopathic TTP experience a relapse (Case 2). Most relapses occur within the first 2 years after the initial episode, with an estimated risk of 43% for relapse at 7.5 years.^5,9

Factors that predict a higher risk of relapse include persistently severely decreased ADAMTS13 activity, positive inhibitor, and high titers of autoantibodies to ADAMTS13 during symptomatic TTP. During clinical remission, persistence of autoantibodies also indicates increased risk.^1,3,5,6,9

Patients who have a relapse and whose disease is refractory to therapeutic plasma exchange (10%–20% of cases) have been treated with corticosteroids, splenectomy, or immunosuppressive agents (cyclosporine, azathioprine, or cyclophosphamide) with varying rates of success. Rituximab (monoclonal anti-CD20) has recently been used as second-line therapy in refractory or relapsing immune-mediated TTP or idiopathic TTP with neurologic or cardiac symptoms associated with a poor prognosis. Therapy including rituximab results in improved response and progression-free survival.³² Other potential therapies, including recombinant active ADAMTS13, are under investigation.^{9,23,28,30,33,34}

A breakthrough in understanding the pathogenesis of thrombotic thrombocytopenic purpura (TTP) came with the discovery of ADAMTS13 (an abbreviation for “a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13”), a plasma protein that cleaves von Willebrand factor, which interacts with platelets to promote blood clotting. If ADAMTS13 is lacking, unusually large multimers of von Willebrand factor can accumulate and trigger intravascular platelet aggregation and microthrombosis, causing the signs and symptoms of TTP.^1–3

This knowledge has practical applications: we can now measure ADAMTS13 activity, ADAMTS13 inhibitor, and antibodies against ADAMTS13 to help us diagnose TTP and distinguish it from other forms of thrombotic microangiopathy, such as hemolytic-uremic syndrome, that have similar symptoms but require different treatment.

Using case studies, this article describes typical presentations of acute and relapsing TTP; the role of laboratory testing, including the ADAMTS13 assay; how to distinguish TTP from other conditions that present similarly; and how to manage this condition.

A HIGH RISK OF DEATH WITHOUT PLASMA EXCHANGE

TTP is characterized by disseminated microthrombi composed of agglutinated platelets and von Willebrand factor in small vessels. Tissue damage by microthrombi can cause thrombocytopenia (platelet deficiency), microangiopathic hemolytic anemia (loss of red blood cells caused by destructive conditions in small vessels), and multiorgan failure.¹

Untreated TTP has a mortality rate of about 90%.¹ As shown in Case 1, Case 2, and Table 1, rapid diagnosis and prompt initiation of daily therapeutic plasma exchange can improve this grave outlook.⁴

ADAMTS13 DEFICIENCY CAN BE ACQUIRED OR CONGENITAL

Two major forms of TTP with ADAMTS13 deficiency and microvascular thrombosis are recognized:

Acquired TTP, the more common form, peaks in incidence between ages 30 and 50.^2,5 It more often affects women, particularly during and after pregnancy (its estimated prevalence is 1 in 25,000 pregnancies), and African Americans.⁶ Acquired TTP may be:

• Primary (idiopathic or autoantibody-mediated), associated with severely decreased ADAMTS13 and the presence of ultra-large von Willebrand factor multimers, or
• Secondary (23%–67% of cases), arising from a variety of conditions, including autoimmune disorders (eg, systemic lupus erythematosus, rheumatoid arthritis), solid organ or hematopoietic cell transplant, malignancy, drugs, and pregnancy (Table 2).^1,5–8 Secondary TTP has a worse prognosis than idiopathic TTP.^5,9

Congenital TTP (Upshaw-Shulman syndrome) is a rare autosomal-recessive disease caused by compound heterozygous or homozygous mutations of the ADAMTS13 gene, producing nonfunctional ADAMTS13 protein. Patients have severely deficient ADAMTS13 activity but usually do not develop autoantibodies. There is a high risk of chronic, relapsing episodes; identified triggers include pregnancy and heavy alcohol intake.^2,10 About half of patients with congenital TTP have an early onset, usually presenting with acute TTP between birth and age 5, and about half have a late onset, usually remaining without symptoms until age 20 to 40.

THE CLINICAL PICTURE OF TTP IS NOT ALWAYS CLASSIC

TTP is primarily diagnosed clinically, but diagnosis is often difficult because of various nonspecific symptoms. Typical TTP presents with the “classic pentad”:

• Severe thrombocytopenia (70%–100% of patients)
• Microangiopathic hemolytic anemia with multiple schistocytes (70%–100%) (Figure 1)
• Neurologic involvement (50%–90%)
• Renal abnormalities (about 50%)
• Fever (25%).

However, the entire picture often does not emerge in a single patient.^2,6 Waiting for the entire pentad to develop before diagnosing TTP can have grave clinical consequences,^1,2,5 and the presence of thrombocytopenia and unexplained microangiopathic hemolytic anemia are considered clinically sufficient to suspect TTP.⁵

Neurologic symptoms usually fluctuate. They can include mild abnormalities such as weakness, dizziness, headache, blurred vision, ataxia, and transient mental status changes, as well as severe abnormalities including stroke, seizure, and coma.^2,6

Most patients have normal findings on computed tomography and magnetic resonance imaging at the onset of neurologic symptoms or with a history of TTP. Some patients (8%–39%) show reversible acute brain lesions, including ischemic changes.^11–13

Other signs and symptoms may result from multiorgan failure due to microthrombosis; ischemia in retinal, coronary, and abdominal circulations; and unconjugated hyperbilirubinemia.²

Atypical presentations. About 18% of patients have cardiac involvement from microvascular occlusion, with arrhythmia, angina, or congestive heart failure. Abdominal pain and pancreatitis occur in 5% to 13%, and visual disturbances in 8% to 10%.

Patients with an atypical presentation may not have laboratory evidence of microangiopathic hemolytic anemia, but an ADAMTS13 assay will show severely decreased activity. Therapeutic plasma exchange can improve atypical symptoms.^2,3,10,14,15

ADAMTS13 ASSAY IS KEY TO DIAGNOSIS

Laboratory evidence typically includes hemolytic anemia (reticulocytosis, schistocytes, elevated indirect bilirubin, reduced haptoglobin, elevated lactate dehydrogenase) and thrombocytopenia.³ There are no significant abnormalities in prothrombin time, international normalized ratio, activated partial thromboplastin time, fibrinogen, or D-dimer level.

Measuring the levels of ADAMTS13 activity, ADAMTS13 inhibitor, and ADAMTS13 antibody is becoming standard to confirm the diagnosis of TTP, to determine if it is congenital or acquired, and to distinguish it from thrombocytopenic conditions such as hemolytic-uremic syndrome, idiopathic thrombocytopenic purpura, and heparin-induced thrombocytopenia.^4,5 A newer ADAMTS13 assay based on fluorescence energy transfer (FRET) technology with a synthetic amino acid-von Willebrand factor peptide substrate has a faster turnaround time and less test variability.^6,16,17 This FRET assay can give the result of ADAMTS13 activity within 2 hours. In comparison, the assay based on multimeric von Willebrand factor takes 2 to 3 days, and mass spectrometry to measure the cleavage products of a synthetic von Willebrand factor molecule takes about 4 hours.^3,10,16

About two-thirds of patients with the clinical diagnosis of idiopathic TTP have ADAMTS13 activity levels lower than 10%.^5,14,18 In the appropriate clinical setting, this threshold level is highly sensitive (89%–100%) and specific (99%–100%) in differentiating TTP from other thrombotic angiopathies.^2,3,18

Note: The ADAMTS13 assay was needed for early correct diagnosis in Case 1 and Case 2.

Inhibitors provide more clues

Autoantibodies can be classified according to whether they inhibit ADAMTS13 activity.

Neutralizing inhibitors. Most cases of acquired, idiopathic TTP with severe ADAMTS13 deficiency are related to circulating autoantibodies that neutralize ADAMTS13 activity. This ADAMTS13 inhibitor level is obtained by measuring residual ADAMTS13 activity after mixing equal amounts of patient plasma with normal pooled plasma. ADAMTS13 inhibitor is detectable in 44% to 93% of patients with severely deficient ADAMTS13 activity.^3,6,19

Nonneutralizing inhibitors. From 10% to 15% of patients with TTP with severe ADAMTS13 deficiency lack ADAMTS13 autoantibodies measured by enzyme immunoassay but have nonneutralizing immunoglobulin G (IgG) or IgM autoantibodies. In such cases, ADAMTS13 deficiency may be related to increased antibody-mediated clearance or other unknown mechanisms.

Neutralizing inhibitors and nonneutralizing inhibitors may be present simultaneously in some patients.^3,10,19,20

Blood factors affect ADAMTS13 activity

Specimen factors can affect ADAMTS13 activity and antibody levels.

Hemoglobin is a potent inhibitor of ADAMTS13, so an elevated plasma level of free hemoglobin (> 2 g/dL) can reduce ADAMTS13 activity, as can hyperbilirubinemia (> 15 mg/dL).

High levels of endogenous von Willebrand factor, lipids, thrombin, or other proteases that may cleave ADAMTS13 can also reduce ADAMTS13 activity.³ Conversely, recent plasma exchange or transfusion can mask the diagnosis of TTP because of false normalization of ADAMTS13 activity. In addition, ADAMTS13 autoantibody can be detected in other immune-mediated disorders (eg, systemic lupus erythematosus, antiphospholipid syndrome), and hypergammaglobulinemia, as well as in 10% to 15% of healthy individuals.¹⁹

CONSIDER OTHER CONDITIONS

Before diagnosing TTP, other conditions causing thrombocytopenia and hemolytic anemia should be excluded by taking a careful clinical, laboratory, and medication history (Table 2). Of these conditions, the most challenging to differentiate from TTP—and often indistinguishable from it at presentation—is hemolytic-uremic syndrome (Table 3).

Hemolytic-uremic syndrome

Hemolytic-uremic syndrome presents with a triad of thrombocytopenia, acute renal failure, and microangiopathic hemolytic anemia, with increased lactate dehydrogenase levels. Renal dysfunction from ischemia or tissue injury by microvascular thrombi predominates. Hemolytic-uremic syndrome most often occurs in children and is often related to hemorrhagic enterocolitis caused by infection with Escherichia coli O157:H7 or Shigella species (90%–95% of cases).^1,2,5

From 5% to 10% of cases of hemolytic- uremic syndrome are atypical. These cases are not associated with diarrhea, and many are caused by genetic mutations that result in chronic excessive complement activation. Implicated genes regulate complement regulator factor H (20%–30% of cases) or CD46 (10%) and other cofactors, or autoantibodies against factor H (10%), which affect the alternate complement pathway.^6,21–23

Initial therapeutic plasma exchange is commonly undertaken for atypical hemolytic- uremic syndrome, particularly for patients at risk of rapid progression to end-stage renal failure. But despite such treatment, about 60% of these patients die or develop permanent renal damage within 1 year.^2,3,24

Eculizumab, a monoclonal antibody against complement component C5, has been approved by the US Food and Drug Administration for atypical hemolytic-uremic syndrome and may improve quality of life.^25–27

PLASMA EXCHANGE IS THE MAINSTAY OF THERAPY

In 2012, the British Society for Haematology published revised guidelines for managing TTP and other thrombotic microangiopathies.²⁸

Acquired idiopathic TTP with reduced ADAMTS13 activity requires immediate therapeutic plasma exchange. Daily plasma exchange combines plasmapheresis to remove circulating ultralarge von Willebrand factor-platelet strings and autoantibodies against ADAMTS13, and infusion of fresh-frozen plasma to replace ADAMTS13.¹⁸ This procedure is the mainstay of therapy and brings 70% to 90% of patients with idiopathic TTP to remission.^1,2,5,6 However, the optimal duration of daily plasma exchange and the number of procedures required is highly variable according to clinical condition. Therapeutic plasma exchange can also cause plasma-related adverse reactions.^9,28 Congenital TTP requires plasma infusion or exchange depending on the patient’s severity of ADAMTS13 deficiency.

Corticosteroids are used in combination with daily therapeutic plasma exchange, although evidence from controlled trials of their efficacy in this setting is lacking. Patients with severely decreased ADAMTS13 activity or low titers of ADAMTS13 autoantibodies tend to respond to the therapy.^5,8,29

An ADAMTS13 assay with a short turn-around time can help guide the decision to initiate therapeutic plasma exchange. However, if there is a strong clinical suspicion of TTP, plasma exchange should be initiated immediately without waiting for test results.^5,30 Monitoring ADAMTS13 activity or inhibitor during initial plasma exchange therapy has had conflicting results in several studies and is generally not recommended for patients with acquired TTP.^8,30,31

RELAPSE IS COMMON

About 20% to 50% of patients with idiopathic TTP experience a relapse (Case 2). Most relapses occur within the first 2 years after the initial episode, with an estimated risk of 43% for relapse at 7.5 years.^5,9

Factors that predict a higher risk of relapse include persistently severely decreased ADAMTS13 activity, positive inhibitor, and high titers of autoantibodies to ADAMTS13 during symptomatic TTP. During clinical remission, persistence of autoantibodies also indicates increased risk.^1,3,5,6,9

Patients who have a relapse and whose disease is refractory to therapeutic plasma exchange (10%–20% of cases) have been treated with corticosteroids, splenectomy, or immunosuppressive agents (cyclosporine, azathioprine, or cyclophosphamide) with varying rates of success. Rituximab (monoclonal anti-CD20) has recently been used as second-line therapy in refractory or relapsing immune-mediated TTP or idiopathic TTP with neurologic or cardiac symptoms associated with a poor prognosis. Therapy including rituximab results in improved response and progression-free survival.³² Other potential therapies, including recombinant active ADAMTS13, are under investigation.^{9,23,28,30,33,34}

A breakthrough in understanding the pathogenesis of thrombotic thrombocytopenic purpura (TTP) came with the discovery of ADAMTS13 (an abbreviation for “a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13”), a plasma protein that cleaves von Willebrand factor, which interacts with platelets to promote blood clotting. If ADAMTS13 is lacking, unusually large multimers of von Willebrand factor can accumulate and trigger intravascular platelet aggregation and microthrombosis, causing the signs and symptoms of TTP.^1–3

This knowledge has practical applications: we can now measure ADAMTS13 activity, ADAMTS13 inhibitor, and antibodies against ADAMTS13 to help us diagnose TTP and distinguish it from other forms of thrombotic microangiopathy, such as hemolytic-uremic syndrome, that have similar symptoms but require different treatment.

Using case studies, this article describes typical presentations of acute and relapsing TTP; the role of laboratory testing, including the ADAMTS13 assay; how to distinguish TTP from other conditions that present similarly; and how to manage this condition.

A HIGH RISK OF DEATH WITHOUT PLASMA EXCHANGE

TTP is characterized by disseminated microthrombi composed of agglutinated platelets and von Willebrand factor in small vessels. Tissue damage by microthrombi can cause thrombocytopenia (platelet deficiency), microangiopathic hemolytic anemia (loss of red blood cells caused by destructive conditions in small vessels), and multiorgan failure.¹

Untreated TTP has a mortality rate of about 90%.¹ As shown in Case 1, Case 2, and Table 1, rapid diagnosis and prompt initiation of daily therapeutic plasma exchange can improve this grave outlook.⁴

ADAMTS13 DEFICIENCY CAN BE ACQUIRED OR CONGENITAL

Two major forms of TTP with ADAMTS13 deficiency and microvascular thrombosis are recognized:

Acquired TTP, the more common form, peaks in incidence between ages 30 and 50.^2,5 It more often affects women, particularly during and after pregnancy (its estimated prevalence is 1 in 25,000 pregnancies), and African Americans.⁶ Acquired TTP may be:

• Primary (idiopathic or autoantibody-mediated), associated with severely decreased ADAMTS13 and the presence of ultra-large von Willebrand factor multimers, or
• Secondary (23%–67% of cases), arising from a variety of conditions, including autoimmune disorders (eg, systemic lupus erythematosus, rheumatoid arthritis), solid organ or hematopoietic cell transplant, malignancy, drugs, and pregnancy (Table 2).^1,5–8 Secondary TTP has a worse prognosis than idiopathic TTP.^5,9

Congenital TTP (Upshaw-Shulman syndrome) is a rare autosomal-recessive disease caused by compound heterozygous or homozygous mutations of the ADAMTS13 gene, producing nonfunctional ADAMTS13 protein. Patients have severely deficient ADAMTS13 activity but usually do not develop autoantibodies. There is a high risk of chronic, relapsing episodes; identified triggers include pregnancy and heavy alcohol intake.^2,10 About half of patients with congenital TTP have an early onset, usually presenting with acute TTP between birth and age 5, and about half have a late onset, usually remaining without symptoms until age 20 to 40.

THE CLINICAL PICTURE OF TTP IS NOT ALWAYS CLASSIC

TTP is primarily diagnosed clinically, but diagnosis is often difficult because of various nonspecific symptoms. Typical TTP presents with the “classic pentad”:

• Severe thrombocytopenia (70%–100% of patients)
• Microangiopathic hemolytic anemia with multiple schistocytes (70%–100%) (Figure 1)
• Neurologic involvement (50%–90%)
• Renal abnormalities (about 50%)
• Fever (25%).

However, the entire picture often does not emerge in a single patient.^2,6 Waiting for the entire pentad to develop before diagnosing TTP can have grave clinical consequences,^1,2,5 and the presence of thrombocytopenia and unexplained microangiopathic hemolytic anemia are considered clinically sufficient to suspect TTP.⁵

Neurologic symptoms usually fluctuate. They can include mild abnormalities such as weakness, dizziness, headache, blurred vision, ataxia, and transient mental status changes, as well as severe abnormalities including stroke, seizure, and coma.^2,6

Most patients have normal findings on computed tomography and magnetic resonance imaging at the onset of neurologic symptoms or with a history of TTP. Some patients (8%–39%) show reversible acute brain lesions, including ischemic changes.^11–13

Other signs and symptoms may result from multiorgan failure due to microthrombosis; ischemia in retinal, coronary, and abdominal circulations; and unconjugated hyperbilirubinemia.²

Atypical presentations. About 18% of patients have cardiac involvement from microvascular occlusion, with arrhythmia, angina, or congestive heart failure. Abdominal pain and pancreatitis occur in 5% to 13%, and visual disturbances in 8% to 10%.

Patients with an atypical presentation may not have laboratory evidence of microangiopathic hemolytic anemia, but an ADAMTS13 assay will show severely decreased activity. Therapeutic plasma exchange can improve atypical symptoms.^2,3,10,14,15

ADAMTS13 ASSAY IS KEY TO DIAGNOSIS

Laboratory evidence typically includes hemolytic anemia (reticulocytosis, schistocytes, elevated indirect bilirubin, reduced haptoglobin, elevated lactate dehydrogenase) and thrombocytopenia.³ There are no significant abnormalities in prothrombin time, international normalized ratio, activated partial thromboplastin time, fibrinogen, or D-dimer level.

Measuring the levels of ADAMTS13 activity, ADAMTS13 inhibitor, and ADAMTS13 antibody is becoming standard to confirm the diagnosis of TTP, to determine if it is congenital or acquired, and to distinguish it from thrombocytopenic conditions such as hemolytic-uremic syndrome, idiopathic thrombocytopenic purpura, and heparin-induced thrombocytopenia.^4,5 A newer ADAMTS13 assay based on fluorescence energy transfer (FRET) technology with a synthetic amino acid-von Willebrand factor peptide substrate has a faster turnaround time and less test variability.^6,16,17 This FRET assay can give the result of ADAMTS13 activity within 2 hours. In comparison, the assay based on multimeric von Willebrand factor takes 2 to 3 days, and mass spectrometry to measure the cleavage products of a synthetic von Willebrand factor molecule takes about 4 hours.^3,10,16

About two-thirds of patients with the clinical diagnosis of idiopathic TTP have ADAMTS13 activity levels lower than 10%.^5,14,18 In the appropriate clinical setting, this threshold level is highly sensitive (89%–100%) and specific (99%–100%) in differentiating TTP from other thrombotic angiopathies.^2,3,18

Note: The ADAMTS13 assay was needed for early correct diagnosis in Case 1 and Case 2.

Inhibitors provide more clues

Autoantibodies can be classified according to whether they inhibit ADAMTS13 activity.

Neutralizing inhibitors. Most cases of acquired, idiopathic TTP with severe ADAMTS13 deficiency are related to circulating autoantibodies that neutralize ADAMTS13 activity. This ADAMTS13 inhibitor level is obtained by measuring residual ADAMTS13 activity after mixing equal amounts of patient plasma with normal pooled plasma. ADAMTS13 inhibitor is detectable in 44% to 93% of patients with severely deficient ADAMTS13 activity.^3,6,19

Nonneutralizing inhibitors. From 10% to 15% of patients with TTP with severe ADAMTS13 deficiency lack ADAMTS13 autoantibodies measured by enzyme immunoassay but have nonneutralizing immunoglobulin G (IgG) or IgM autoantibodies. In such cases, ADAMTS13 deficiency may be related to increased antibody-mediated clearance or other unknown mechanisms.

Neutralizing inhibitors and nonneutralizing inhibitors may be present simultaneously in some patients.^3,10,19,20

Blood factors affect ADAMTS13 activity

Specimen factors can affect ADAMTS13 activity and antibody levels.

Hemoglobin is a potent inhibitor of ADAMTS13, so an elevated plasma level of free hemoglobin (> 2 g/dL) can reduce ADAMTS13 activity, as can hyperbilirubinemia (> 15 mg/dL).

High levels of endogenous von Willebrand factor, lipids, thrombin, or other proteases that may cleave ADAMTS13 can also reduce ADAMTS13 activity.³ Conversely, recent plasma exchange or transfusion can mask the diagnosis of TTP because of false normalization of ADAMTS13 activity. In addition, ADAMTS13 autoantibody can be detected in other immune-mediated disorders (eg, systemic lupus erythematosus, antiphospholipid syndrome), and hypergammaglobulinemia, as well as in 10% to 15% of healthy individuals.¹⁹

CONSIDER OTHER CONDITIONS

Before diagnosing TTP, other conditions causing thrombocytopenia and hemolytic anemia should be excluded by taking a careful clinical, laboratory, and medication history (Table 2). Of these conditions, the most challenging to differentiate from TTP—and often indistinguishable from it at presentation—is hemolytic-uremic syndrome (Table 3).

Hemolytic-uremic syndrome

Hemolytic-uremic syndrome presents with a triad of thrombocytopenia, acute renal failure, and microangiopathic hemolytic anemia, with increased lactate dehydrogenase levels. Renal dysfunction from ischemia or tissue injury by microvascular thrombi predominates. Hemolytic-uremic syndrome most often occurs in children and is often related to hemorrhagic enterocolitis caused by infection with Escherichia coli O157:H7 or Shigella species (90%–95% of cases).^1,2,5

From 5% to 10% of cases of hemolytic- uremic syndrome are atypical. These cases are not associated with diarrhea, and many are caused by genetic mutations that result in chronic excessive complement activation. Implicated genes regulate complement regulator factor H (20%–30% of cases) or CD46 (10%) and other cofactors, or autoantibodies against factor H (10%), which affect the alternate complement pathway.^6,21–23

Initial therapeutic plasma exchange is commonly undertaken for atypical hemolytic- uremic syndrome, particularly for patients at risk of rapid progression to end-stage renal failure. But despite such treatment, about 60% of these patients die or develop permanent renal damage within 1 year.^2,3,24

Eculizumab, a monoclonal antibody against complement component C5, has been approved by the US Food and Drug Administration for atypical hemolytic-uremic syndrome and may improve quality of life.^25–27

PLASMA EXCHANGE IS THE MAINSTAY OF THERAPY

In 2012, the British Society for Haematology published revised guidelines for managing TTP and other thrombotic microangiopathies.²⁸

Acquired idiopathic TTP with reduced ADAMTS13 activity requires immediate therapeutic plasma exchange. Daily plasma exchange combines plasmapheresis to remove circulating ultralarge von Willebrand factor-platelet strings and autoantibodies against ADAMTS13, and infusion of fresh-frozen plasma to replace ADAMTS13.¹⁸ This procedure is the mainstay of therapy and brings 70% to 90% of patients with idiopathic TTP to remission.^1,2,5,6 However, the optimal duration of daily plasma exchange and the number of procedures required is highly variable according to clinical condition. Therapeutic plasma exchange can also cause plasma-related adverse reactions.^9,28 Congenital TTP requires plasma infusion or exchange depending on the patient’s severity of ADAMTS13 deficiency.

Corticosteroids are used in combination with daily therapeutic plasma exchange, although evidence from controlled trials of their efficacy in this setting is lacking. Patients with severely decreased ADAMTS13 activity or low titers of ADAMTS13 autoantibodies tend to respond to the therapy.^5,8,29

An ADAMTS13 assay with a short turn-around time can help guide the decision to initiate therapeutic plasma exchange. However, if there is a strong clinical suspicion of TTP, plasma exchange should be initiated immediately without waiting for test results.^5,30 Monitoring ADAMTS13 activity or inhibitor during initial plasma exchange therapy has had conflicting results in several studies and is generally not recommended for patients with acquired TTP.^8,30,31

RELAPSE IS COMMON

About 20% to 50% of patients with idiopathic TTP experience a relapse (Case 2). Most relapses occur within the first 2 years after the initial episode, with an estimated risk of 43% for relapse at 7.5 years.^5,9

Factors that predict a higher risk of relapse include persistently severely decreased ADAMTS13 activity, positive inhibitor, and high titers of autoantibodies to ADAMTS13 during symptomatic TTP. During clinical remission, persistence of autoantibodies also indicates increased risk.^1,3,5,6,9

Patients who have a relapse and whose disease is refractory to therapeutic plasma exchange (10%–20% of cases) have been treated with corticosteroids, splenectomy, or immunosuppressive agents (cyclosporine, azathioprine, or cyclophosphamide) with varying rates of success. Rituximab (monoclonal anti-CD20) has recently been used as second-line therapy in refractory or relapsing immune-mediated TTP or idiopathic TTP with neurologic or cardiac symptoms associated with a poor prognosis. Therapy including rituximab results in improved response and progression-free survival.³² Other potential therapies, including recombinant active ADAMTS13, are under investigation.^{9,23,28,30,33,34}

A 20-year-old woman with Gaucher disease presents with pain in her right ankle and in her back. She has had the ankle pain for the past 12 months and the back pain for the past 2 years. She describes the ankle pain as stabbing and moderately severe. It is constant, present both at rest and during physical activity, but aggravated by walking and twisting movements. She has noticed grinding and clicking sounds as she moves her ankle. The ankle pain has worsened over the past several months.

She says her back pain is similar to her ankle pain but less severe. She also reports generalized mild aches and bone pain. No other joints are involved. She has no history of fever, chills, or trauma.

A COMPLICATED MEDICAL HISTORY

Her Gaucher disease was diagnosed at age 4 when she presented with failure to thrive and with thrombocytopenia and splenomegaly. She and was found to have an N370S/IVS2+1 mutation of the GBA gene. She underwent removal of 90% of her spleen at the time of diagnosis and was on enzyme replacement therapy with imiglucerase until 3 years ago, when the treatment was stopped because the drug had become unavailable (because of a temporary closure of the manufacturing facility), and because she had developed neutralizing antibodies to it. Despite a dosage as high as 120 U/kg every 2 weeks (the recommended range is 2.5 U/kg three times a week up to 60 U/kg every 2 weeks), her anemia and thrombocytopenia worsened to the point that she became dependent on transfusion of red blood cells and platelets. She has also taken glucocorticoids at various times in the past as a premedication before enzyme replacement therapy.

About 3 years ago, she developed dryness of the skin, pruritus, shiny skin, hardening of the skin, and decreased oral aperture, which was diagnosed as scleroderma.

During the past 5 years, she has had multiple episodes of pale coloration of her skin on exposure to cold, suggestive of Raynaud phenomenon. And for the past 5 months, she has noticed a burning sensation in her throat and retrosternal pain, suggestive of gastroesophageal reflux disease.

She is a college student, with no history of smoking or use of alcohol or recreational drugs. She is sexually active, with no history of sexually transmitted disease, and she uses condoms and oral contraceptives for contraception.

Her father and mother are both carriers of Gaucher disease. She is not of Ashkenazi Jewish descent.

FINDINGS ON PHYSICAL EXAMINATION

On physical examination, her temperature, blood pressure, pulse, and respiratory rate are within normal limits. She has extensive tattooing on her upper chest to hide scarring from previous cannulation ports. The right ankle joint is moderately swollen but shows no other signs of inflammation; its range of motion is limited by severe pain. She has tenderness of the spinous processes and paraspinal area, in addition to multiple tender points in the thoracolumbar area. Palpation of the right hip reveals tenderness of the groin and trochanteric bursa.

No lymphadenopathy, hepatomegaly, splenomegaly, or abdominal masses are noted. Neurologic examination is essentially nonfocal.

Her current medications include omeprazole, ergocalciferol, calcium carbonate, gabapentin, citalopram, and celecoxib. She also takes a multivitamin daily.

1. Which is the most likely underlying cause of her ankle pain?

• Rheumatoid arthritis
• Gaucher disease
• Septic arthritis
• Avascular necrosis secondary to steroid use

Rheumatoid arthritis varies in its presentation. It is usually insidious in onset, migratory, and intermittent, with polyarticular or even monoarticular involvement, and it presents with pain, stiffness, and swelling of the joint.¹ Most often affected are the metacarpophalangeal, proximal interphalangeal, wrist, and metatarsophalangeal joints. Involvement of large joints of the upper and lower limbs is also common.² This is not the most likely cause of this patient’s symptoms, based on the history and the current presentation.

Gaucher disease is a lipidosis caused by accumulation of cellular glycolipids, especially glucocerebrosides, due to deficiency of the enzyme beta-glucosidase. Clinical manifestations include hepatomegaly, splenomegaly, and bone marrow disease presenting as anemia, thrombocytopenia, or skeletal disease.³ Skeletal involvement in Gaucher disease includes bone pain, bone infarcts, and lytic lesions.

Whether splenectomy predisposes the patient to bone manifestations is controversial. Some believe that splenectomy decreases the total body reservoir for the storage of glycolipids and predisposes to their deposition in bone, which in turn results in cortical thinning, impaired remodeling, and decreased intraosseous blood flow, leading to osteonecrosis and fractures.⁴ This is more common in patients with type 1 Gaucher disease who have undergone splenectomy. (Types 2 and 3 are much rarer, occurring mainly in children; central nervous system involvement is a key feature. A discussion of these types is beyond the focus of this paper.) However, some studies suggest that the increase in bone manifestations after splenectomy may be simply because of severe disease.⁵ It should be noted that, since the advent of enzyme replacement therapy for Gaucher disease, splenectomy is now rarely performed.⁶

Anemia is also considered an independent risk factor for the development of avascular necrosis in type 1 Gaucher disease.⁷ Osteonecrosis due to Gaucher disease is relatively common in the femur, tibia, and humerus and uncommon in the ankle joints.⁸

Septic arthritis is unlikely in this patient in the absence of fever or signs of inflammation of the joint. Her long-standing history of ankle pain would also be unusual for infection, but a superimposed infectious process should always be suspected in an arthritic joint.

Avascular necrosis secondary to steroid use. Glucocorticoids are notorious for their adverse effects on bone. They induce osteocyte apoptosis and a decrease in bone remodeling, potentially predisposing to osteonecrosis.⁹ There is a high incidence of osteoporosis, osteonecrosis, and fracture risk with glucocorticoid therapy, and the incidence is dose-dependent. Discontinuation of the drug only partially restores fracture risk to baseline levels.^10,11

A meta-analysis of cohort studies with a total sample size of about 42,000 reported an increased risk of fracture at all ages with the use of glucocorticoids.¹² Because the minimum dosage and duration of therapy to prevent glucocorticoid-induced osteoporosis are not known, the only recommendation is to keep the dosage as low as possible.¹³

Glucocorticoid therapy is the most common cause of nontraumatic avascular necrosis. The risk of osteonecrosis in patients on long-term glucocorticoid therapy may be as high as 40%.¹⁴ The risk is increased with prolonged treatment and with high doses, but it can also occur with short-term exposure to high doses. The increased risk has been shown to persist for as long as 2 years after the drugs are discontinued.¹⁵ Glucocorticoid-induced bone disease commonly affects the hip and vertebrae.

At this stage of the workup, we cannot completely rule out glucocorticoid use as the cause. However, after considering this patient’s presentation and the key features of the other diagnoses, her ankle pain and back pain are more likely caused by her preexisting Gaucher disease.

CONTINUED EVALUATION


Initial laboratory tests (Table 1) reveal severe anemia and thrombocytopenia. Bone marrow biopsy of the iliac crest done as part of the workup for these conditions shows extensive bone marrow space replacement by histiocytic infiltrate, consistent with Gaucher disease. No other marrow process is observed.

Radiography of the ankle (Figure 1) shows a subtle lucency in the talar dome with minimal subarticular collapse seen on the lateral view, suggestive of avascular necrosis and diffuse osteopenia. Joint spaces are maintained.

Magnetic resonance imaging (MRI) of the ankle shows numerous bone infarcts with an approximately 15-mm region of mild articular surface collapse in the central and lateral aspect of the talar dome.

MRI of the back shows extensive abnormal bone marrow signal intensity throughout the spine, compatible with a marrow replacement process. Patchy nonexpansile T2/stir hyperintensity with serpiginous enhancement within the T9, T11, T12, L2, and L3 vertebral bodies as well as throughout the entire sacrum is consistent with bone infarct.

2. Based on the results of radiographic studies, which is most likely the immediate cause of her ankle pain?

• Talar avascular necrosis secondary to rheumatoid arthritis
• Talar avascular necrosis secondary to Gaucher disease
• Trauma-induced fracture of the talus
• Plantar fasciitis

Of the bones of the feet, the talus is unique. It is the second largest of the tarsal bones and does not have muscular or tendinous attachments. Sixty percent of the talus bone is covered by articular cartilage,¹⁶ so only a limited area is available for penetration of blood vessels. Also, small nutrient vessels and variations of intraosseous anastomoses with a lack of collateral circulation predispose the talus to osteonecrosis when the vascular supply is compromised.¹⁶

Radiographic evidence of avascular necrosis is the presence of bone that is more radiopaque than normal bone; this is necrotic bone surrounded by osteopenic bone. Avascular necrosis causes hyperemia and resorption of bone. The resorption does not take place in necrotic bone because of the lack of a vascular supply, and so it appears radiopaque, whereas the bone surrounding the necrotic bone becomes osteopenic and radiolucent.

The sclerotic rim of a bone infarct is also enhanced by an attempted healing process in which new bone forms on the surface of necrotic trabeculae, a process known as “creeping substitution.” This gives a typical sclerotic picture of the talus.

MRI is the most sensitive technique for detecting osteonecrosis. A characteristic radiographic pattern is seen with osteonecrosis of the talus starting with talar dome opacity, followed by deformity and, in severe cases, articular collapse and bone fragmentation.¹⁷

The radiograph in our patient’s case is not consistent with features of rheumatoid arthritis or traumatic fracture of the talus. In plantar fasciitis, radiographs are used to rule out other pathologies of the foot, and the only finding may be a bone spur seen at the site of pain. The bone spur is not the cause of pain in plantar fasciitis but may be a result of the plantar fasciitis itself.

Therefore, avascular necrosis secondary to Gaucher disease is most likely the immediate cause of her ankle pain.

THE COURSE OF TREATMENT

The patient is started on enzyme replacement therapy with taliglucerase alfa (see discussion of enzyme replacement below). For the ankle pain, conservative management is prescribed, with application of a splint and a boot.

After 4 months of conservative management, radiography (Figure 2) and magnetic resonance imaging (Figure 3) show progressive deterioration of the talus body, and her ankle pain has worsened. A 6-week trial of an ankle brace also proves futile. Her pain continues to worsen and is not controllable with high doses of pain medication. She requests below-the-knee amputation.

Given the complexity of this patient’s medical condition, fusion of the ankle and hindfoot—which in some patients is preferable to amputation—is not considered because of her extensive bone involvement and ongoing thrombocytopenia, which would impede healing after the procedure. Below-the-knee amputation is performed without complications.

Study of the specimen after amputation reveals talar bone necrosis and bone marrow infiltration by foamy macrophages, consistent with Gaucher disease (Figures 4–6).

GAUCHER DISEASE

Pharmacologic treatments, effective only for type 1 Gaucher disease, target hepatosplenomegaly, cytopenia, and bone manifestations. Two approaches are enzyme replacement therapy—ie, to replace the defective enzyme—and substrate reduction therapy—ie, to reduce the production and thus the accumulation of glucocerebroside. Enzyme replacement is the first choice of therapy; substrate reduction is reserved for patients unable to tolerate enzyme replacement therapy.

Enzyme replacement

Current drugs for enzyme replacement therapy are imiglucerase, taliglucerase alfa, and velaglucerase alfa. The drugs are given by intravenous infusion over 1 to 2 hours in an outpatient clinic or office every 2 weeks.

These drugs are extremely expensive. Currently, the estimated cost of therapy for 1 year would be $432,978 for imiglucerase, $324,870 for taliglucerase alfa, and $368,550 for velaglucerase alfa. (The estimated costs are for 1 year of treatment for a 70-kg patient at 60 U/kg every 2 weeks.)¹⁸ Taliglucerase alfa is less expensive than the other two because it is plant-derived and thus can be more readily produced on a large scale.¹⁹

Substrate reduction

Current drugs for substrate reduction therapy are eliglustat and miglustat. They are given orally. Eliglustat is the first oral drug approved as a first-line treatment for Gaucher disease.²⁰ Miglustat is approved only for mild to moderate disease when enzyme replacement fails or is not tolerated.

Patients can develop antibodies to any of the enzyme replacement drugs. It is not known whether this antibody response differs among the three drugs.²¹

Avascular necrosis of bone can occur in many clinical settings especially after a fracture, particularly of the head of the femur, which leads to interruption of blood supply to the area. Patients with sickle cell disease, those on corticosteroids or bisphosphonates (the latter causing osteonecrosis of the jaw), and those who have pancreatitis or human immunodeficiency virus infection are more prone to this bone complication.

In Gaucher disease, osteonecrosis is associated with splenectomy and severe disease and tends to occur at a younger age than in patients with other diagnoses.⁸ The plasma chitotriosidase activity and pulmonary and activation-regulated chemokines (PARC/CCL18), which are 10 to 40 times higher than normal in symptomatic patients with Gaucher disease, can be used as a biomarker of disease activity.⁸ Only plasma chitotriosidase is clinically available and used on a routine basis.

Bone involvement is seen in approximately 75% of the patients with type 1 Gaucher disease,²² and osteonecrosis is a severe form of bone involvement. Monitoring of patients for bone involvement is recommended. Enzyme replacement therapy for Gaucher disease needs to be started even if visceral disease is absent if the patient has evidence of bone involvement in the form of avascular necrosis.⁷ Prospective studies have shown that enzyme replacement therapy reduces the incidence of osteonecrosis.²³

FOLLOW-UP MANAGEMENT OF OUR PATIENT

Avascular necrosis in Gaucher disease more typically involves the hips and shoulders. In the case of our patient, the talus was the most affected bone. Other contributing factors may have been the use of steroids as a premedication (often unnecessary) for her enzyme replacement therapy, as well as the coexistent scleroderma.²⁴

The decision to switch from imiglucerase, to which she developed antibodies, to taliglucerase was made in the hope that the antibodies would not cross-react. After she started taliglucerase, her complete blood count values improved steadily. She did not require transfusions for more than 1 year. Her platelet count rose to 90 × 10⁹/L, and her hemoglobin to 12 g/dL.

A multidisciplinary approach with regular monitoring and appropriate initiation of therapy is necessary to prevent disastrous complications in patients with Gaucher disease.

A 20-year-old woman with Gaucher disease presents with pain in her right ankle and in her back. She has had the ankle pain for the past 12 months and the back pain for the past 2 years. She describes the ankle pain as stabbing and moderately severe. It is constant, present both at rest and during physical activity, but aggravated by walking and twisting movements. She has noticed grinding and clicking sounds as she moves her ankle. The ankle pain has worsened over the past several months.

She says her back pain is similar to her ankle pain but less severe. She also reports generalized mild aches and bone pain. No other joints are involved. She has no history of fever, chills, or trauma.

A COMPLICATED MEDICAL HISTORY

Her Gaucher disease was diagnosed at age 4 when she presented with failure to thrive and with thrombocytopenia and splenomegaly. She and was found to have an N370S/IVS2+1 mutation of the GBA gene. She underwent removal of 90% of her spleen at the time of diagnosis and was on enzyme replacement therapy with imiglucerase until 3 years ago, when the treatment was stopped because the drug had become unavailable (because of a temporary closure of the manufacturing facility), and because she had developed neutralizing antibodies to it. Despite a dosage as high as 120 U/kg every 2 weeks (the recommended range is 2.5 U/kg three times a week up to 60 U/kg every 2 weeks), her anemia and thrombocytopenia worsened to the point that she became dependent on transfusion of red blood cells and platelets. She has also taken glucocorticoids at various times in the past as a premedication before enzyme replacement therapy.

About 3 years ago, she developed dryness of the skin, pruritus, shiny skin, hardening of the skin, and decreased oral aperture, which was diagnosed as scleroderma.

During the past 5 years, she has had multiple episodes of pale coloration of her skin on exposure to cold, suggestive of Raynaud phenomenon. And for the past 5 months, she has noticed a burning sensation in her throat and retrosternal pain, suggestive of gastroesophageal reflux disease.

She is a college student, with no history of smoking or use of alcohol or recreational drugs. She is sexually active, with no history of sexually transmitted disease, and she uses condoms and oral contraceptives for contraception.

Her father and mother are both carriers of Gaucher disease. She is not of Ashkenazi Jewish descent.

FINDINGS ON PHYSICAL EXAMINATION

On physical examination, her temperature, blood pressure, pulse, and respiratory rate are within normal limits. She has extensive tattooing on her upper chest to hide scarring from previous cannulation ports. The right ankle joint is moderately swollen but shows no other signs of inflammation; its range of motion is limited by severe pain. She has tenderness of the spinous processes and paraspinal area, in addition to multiple tender points in the thoracolumbar area. Palpation of the right hip reveals tenderness of the groin and trochanteric bursa.

No lymphadenopathy, hepatomegaly, splenomegaly, or abdominal masses are noted. Neurologic examination is essentially nonfocal.

Her current medications include omeprazole, ergocalciferol, calcium carbonate, gabapentin, citalopram, and celecoxib. She also takes a multivitamin daily.

1. Which is the most likely underlying cause of her ankle pain?

• Rheumatoid arthritis
• Gaucher disease
• Septic arthritis
• Avascular necrosis secondary to steroid use

Rheumatoid arthritis varies in its presentation. It is usually insidious in onset, migratory, and intermittent, with polyarticular or even monoarticular involvement, and it presents with pain, stiffness, and swelling of the joint.¹ Most often affected are the metacarpophalangeal, proximal interphalangeal, wrist, and metatarsophalangeal joints. Involvement of large joints of the upper and lower limbs is also common.² This is not the most likely cause of this patient’s symptoms, based on the history and the current presentation.

Gaucher disease is a lipidosis caused by accumulation of cellular glycolipids, especially glucocerebrosides, due to deficiency of the enzyme beta-glucosidase. Clinical manifestations include hepatomegaly, splenomegaly, and bone marrow disease presenting as anemia, thrombocytopenia, or skeletal disease.³ Skeletal involvement in Gaucher disease includes bone pain, bone infarcts, and lytic lesions.

Whether splenectomy predisposes the patient to bone manifestations is controversial. Some believe that splenectomy decreases the total body reservoir for the storage of glycolipids and predisposes to their deposition in bone, which in turn results in cortical thinning, impaired remodeling, and decreased intraosseous blood flow, leading to osteonecrosis and fractures.⁴ This is more common in patients with type 1 Gaucher disease who have undergone splenectomy. (Types 2 and 3 are much rarer, occurring mainly in children; central nervous system involvement is a key feature. A discussion of these types is beyond the focus of this paper.) However, some studies suggest that the increase in bone manifestations after splenectomy may be simply because of severe disease.⁵ It should be noted that, since the advent of enzyme replacement therapy for Gaucher disease, splenectomy is now rarely performed.⁶

Anemia is also considered an independent risk factor for the development of avascular necrosis in type 1 Gaucher disease.⁷ Osteonecrosis due to Gaucher disease is relatively common in the femur, tibia, and humerus and uncommon in the ankle joints.⁸

Septic arthritis is unlikely in this patient in the absence of fever or signs of inflammation of the joint. Her long-standing history of ankle pain would also be unusual for infection, but a superimposed infectious process should always be suspected in an arthritic joint.

Avascular necrosis secondary to steroid use. Glucocorticoids are notorious for their adverse effects on bone. They induce osteocyte apoptosis and a decrease in bone remodeling, potentially predisposing to osteonecrosis.⁹ There is a high incidence of osteoporosis, osteonecrosis, and fracture risk with glucocorticoid therapy, and the incidence is dose-dependent. Discontinuation of the drug only partially restores fracture risk to baseline levels.^10,11

A meta-analysis of cohort studies with a total sample size of about 42,000 reported an increased risk of fracture at all ages with the use of glucocorticoids.¹² Because the minimum dosage and duration of therapy to prevent glucocorticoid-induced osteoporosis are not known, the only recommendation is to keep the dosage as low as possible.¹³

Glucocorticoid therapy is the most common cause of nontraumatic avascular necrosis. The risk of osteonecrosis in patients on long-term glucocorticoid therapy may be as high as 40%.¹⁴ The risk is increased with prolonged treatment and with high doses, but it can also occur with short-term exposure to high doses. The increased risk has been shown to persist for as long as 2 years after the drugs are discontinued.¹⁵ Glucocorticoid-induced bone disease commonly affects the hip and vertebrae.

At this stage of the workup, we cannot completely rule out glucocorticoid use as the cause. However, after considering this patient’s presentation and the key features of the other diagnoses, her ankle pain and back pain are more likely caused by her preexisting Gaucher disease.

CONTINUED EVALUATION


Initial laboratory tests (Table 1) reveal severe anemia and thrombocytopenia. Bone marrow biopsy of the iliac crest done as part of the workup for these conditions shows extensive bone marrow space replacement by histiocytic infiltrate, consistent with Gaucher disease. No other marrow process is observed.

Radiography of the ankle (Figure 1) shows a subtle lucency in the talar dome with minimal subarticular collapse seen on the lateral view, suggestive of avascular necrosis and diffuse osteopenia. Joint spaces are maintained.

Magnetic resonance imaging (MRI) of the ankle shows numerous bone infarcts with an approximately 15-mm region of mild articular surface collapse in the central and lateral aspect of the talar dome.

MRI of the back shows extensive abnormal bone marrow signal intensity throughout the spine, compatible with a marrow replacement process. Patchy nonexpansile T2/stir hyperintensity with serpiginous enhancement within the T9, T11, T12, L2, and L3 vertebral bodies as well as throughout the entire sacrum is consistent with bone infarct.

2. Based on the results of radiographic studies, which is most likely the immediate cause of her ankle pain?

• Talar avascular necrosis secondary to rheumatoid arthritis
• Talar avascular necrosis secondary to Gaucher disease
• Trauma-induced fracture of the talus
• Plantar fasciitis

Of the bones of the feet, the talus is unique. It is the second largest of the tarsal bones and does not have muscular or tendinous attachments. Sixty percent of the talus bone is covered by articular cartilage,¹⁶ so only a limited area is available for penetration of blood vessels. Also, small nutrient vessels and variations of intraosseous anastomoses with a lack of collateral circulation predispose the talus to osteonecrosis when the vascular supply is compromised.¹⁶

Radiographic evidence of avascular necrosis is the presence of bone that is more radiopaque than normal bone; this is necrotic bone surrounded by osteopenic bone. Avascular necrosis causes hyperemia and resorption of bone. The resorption does not take place in necrotic bone because of the lack of a vascular supply, and so it appears radiopaque, whereas the bone surrounding the necrotic bone becomes osteopenic and radiolucent.

The sclerotic rim of a bone infarct is also enhanced by an attempted healing process in which new bone forms on the surface of necrotic trabeculae, a process known as “creeping substitution.” This gives a typical sclerotic picture of the talus.

MRI is the most sensitive technique for detecting osteonecrosis. A characteristic radiographic pattern is seen with osteonecrosis of the talus starting with talar dome opacity, followed by deformity and, in severe cases, articular collapse and bone fragmentation.¹⁷

The radiograph in our patient’s case is not consistent with features of rheumatoid arthritis or traumatic fracture of the talus. In plantar fasciitis, radiographs are used to rule out other pathologies of the foot, and the only finding may be a bone spur seen at the site of pain. The bone spur is not the cause of pain in plantar fasciitis but may be a result of the plantar fasciitis itself.

Therefore, avascular necrosis secondary to Gaucher disease is most likely the immediate cause of her ankle pain.

THE COURSE OF TREATMENT

The patient is started on enzyme replacement therapy with taliglucerase alfa (see discussion of enzyme replacement below). For the ankle pain, conservative management is prescribed, with application of a splint and a boot.

After 4 months of conservative management, radiography (Figure 2) and magnetic resonance imaging (Figure 3) show progressive deterioration of the talus body, and her ankle pain has worsened. A 6-week trial of an ankle brace also proves futile. Her pain continues to worsen and is not controllable with high doses of pain medication. She requests below-the-knee amputation.

Given the complexity of this patient’s medical condition, fusion of the ankle and hindfoot—which in some patients is preferable to amputation—is not considered because of her extensive bone involvement and ongoing thrombocytopenia, which would impede healing after the procedure. Below-the-knee amputation is performed without complications.

Study of the specimen after amputation reveals talar bone necrosis and bone marrow infiltration by foamy macrophages, consistent with Gaucher disease (Figures 4–6).

GAUCHER DISEASE

Pharmacologic treatments, effective only for type 1 Gaucher disease, target hepatosplenomegaly, cytopenia, and bone manifestations. Two approaches are enzyme replacement therapy—ie, to replace the defective enzyme—and substrate reduction therapy—ie, to reduce the production and thus the accumulation of glucocerebroside. Enzyme replacement is the first choice of therapy; substrate reduction is reserved for patients unable to tolerate enzyme replacement therapy.

Enzyme replacement

Current drugs for enzyme replacement therapy are imiglucerase, taliglucerase alfa, and velaglucerase alfa. The drugs are given by intravenous infusion over 1 to 2 hours in an outpatient clinic or office every 2 weeks.

These drugs are extremely expensive. Currently, the estimated cost of therapy for 1 year would be $432,978 for imiglucerase, $324,870 for taliglucerase alfa, and $368,550 for velaglucerase alfa. (The estimated costs are for 1 year of treatment for a 70-kg patient at 60 U/kg every 2 weeks.)¹⁸ Taliglucerase alfa is less expensive than the other two because it is plant-derived and thus can be more readily produced on a large scale.¹⁹

Substrate reduction

Current drugs for substrate reduction therapy are eliglustat and miglustat. They are given orally. Eliglustat is the first oral drug approved as a first-line treatment for Gaucher disease.²⁰ Miglustat is approved only for mild to moderate disease when enzyme replacement fails or is not tolerated.

Patients can develop antibodies to any of the enzyme replacement drugs. It is not known whether this antibody response differs among the three drugs.²¹

Avascular necrosis of bone can occur in many clinical settings especially after a fracture, particularly of the head of the femur, which leads to interruption of blood supply to the area. Patients with sickle cell disease, those on corticosteroids or bisphosphonates (the latter causing osteonecrosis of the jaw), and those who have pancreatitis or human immunodeficiency virus infection are more prone to this bone complication.

In Gaucher disease, osteonecrosis is associated with splenectomy and severe disease and tends to occur at a younger age than in patients with other diagnoses.⁸ The plasma chitotriosidase activity and pulmonary and activation-regulated chemokines (PARC/CCL18), which are 10 to 40 times higher than normal in symptomatic patients with Gaucher disease, can be used as a biomarker of disease activity.⁸ Only plasma chitotriosidase is clinically available and used on a routine basis.

Bone involvement is seen in approximately 75% of the patients with type 1 Gaucher disease,²² and osteonecrosis is a severe form of bone involvement. Monitoring of patients for bone involvement is recommended. Enzyme replacement therapy for Gaucher disease needs to be started even if visceral disease is absent if the patient has evidence of bone involvement in the form of avascular necrosis.⁷ Prospective studies have shown that enzyme replacement therapy reduces the incidence of osteonecrosis.²³

FOLLOW-UP MANAGEMENT OF OUR PATIENT

Avascular necrosis in Gaucher disease more typically involves the hips and shoulders. In the case of our patient, the talus was the most affected bone. Other contributing factors may have been the use of steroids as a premedication (often unnecessary) for her enzyme replacement therapy, as well as the coexistent scleroderma.²⁴

The decision to switch from imiglucerase, to which she developed antibodies, to taliglucerase was made in the hope that the antibodies would not cross-react. After she started taliglucerase, her complete blood count values improved steadily. She did not require transfusions for more than 1 year. Her platelet count rose to 90 × 10⁹/L, and her hemoglobin to 12 g/dL.

A multidisciplinary approach with regular monitoring and appropriate initiation of therapy is necessary to prevent disastrous complications in patients with Gaucher disease.

A 20-year-old woman with Gaucher disease presents with pain in her right ankle and in her back. She has had the ankle pain for the past 12 months and the back pain for the past 2 years. She describes the ankle pain as stabbing and moderately severe. It is constant, present both at rest and during physical activity, but aggravated by walking and twisting movements. She has noticed grinding and clicking sounds as she moves her ankle. The ankle pain has worsened over the past several months.

She says her back pain is similar to her ankle pain but less severe. She also reports generalized mild aches and bone pain. No other joints are involved. She has no history of fever, chills, or trauma.

A COMPLICATED MEDICAL HISTORY

Her Gaucher disease was diagnosed at age 4 when she presented with failure to thrive and with thrombocytopenia and splenomegaly. She and was found to have an N370S/IVS2+1 mutation of the GBA gene. She underwent removal of 90% of her spleen at the time of diagnosis and was on enzyme replacement therapy with imiglucerase until 3 years ago, when the treatment was stopped because the drug had become unavailable (because of a temporary closure of the manufacturing facility), and because she had developed neutralizing antibodies to it. Despite a dosage as high as 120 U/kg every 2 weeks (the recommended range is 2.5 U/kg three times a week up to 60 U/kg every 2 weeks), her anemia and thrombocytopenia worsened to the point that she became dependent on transfusion of red blood cells and platelets. She has also taken glucocorticoids at various times in the past as a premedication before enzyme replacement therapy.

About 3 years ago, she developed dryness of the skin, pruritus, shiny skin, hardening of the skin, and decreased oral aperture, which was diagnosed as scleroderma.

During the past 5 years, she has had multiple episodes of pale coloration of her skin on exposure to cold, suggestive of Raynaud phenomenon. And for the past 5 months, she has noticed a burning sensation in her throat and retrosternal pain, suggestive of gastroesophageal reflux disease.

She is a college student, with no history of smoking or use of alcohol or recreational drugs. She is sexually active, with no history of sexually transmitted disease, and she uses condoms and oral contraceptives for contraception.

Her father and mother are both carriers of Gaucher disease. She is not of Ashkenazi Jewish descent.

FINDINGS ON PHYSICAL EXAMINATION

On physical examination, her temperature, blood pressure, pulse, and respiratory rate are within normal limits. She has extensive tattooing on her upper chest to hide scarring from previous cannulation ports. The right ankle joint is moderately swollen but shows no other signs of inflammation; its range of motion is limited by severe pain. She has tenderness of the spinous processes and paraspinal area, in addition to multiple tender points in the thoracolumbar area. Palpation of the right hip reveals tenderness of the groin and trochanteric bursa.

No lymphadenopathy, hepatomegaly, splenomegaly, or abdominal masses are noted. Neurologic examination is essentially nonfocal.

Her current medications include omeprazole, ergocalciferol, calcium carbonate, gabapentin, citalopram, and celecoxib. She also takes a multivitamin daily.

1. Which is the most likely underlying cause of her ankle pain?

• Rheumatoid arthritis
• Gaucher disease
• Septic arthritis
• Avascular necrosis secondary to steroid use

Rheumatoid arthritis varies in its presentation. It is usually insidious in onset, migratory, and intermittent, with polyarticular or even monoarticular involvement, and it presents with pain, stiffness, and swelling of the joint.¹ Most often affected are the metacarpophalangeal, proximal interphalangeal, wrist, and metatarsophalangeal joints. Involvement of large joints of the upper and lower limbs is also common.² This is not the most likely cause of this patient’s symptoms, based on the history and the current presentation.

Gaucher disease is a lipidosis caused by accumulation of cellular glycolipids, especially glucocerebrosides, due to deficiency of the enzyme beta-glucosidase. Clinical manifestations include hepatomegaly, splenomegaly, and bone marrow disease presenting as anemia, thrombocytopenia, or skeletal disease.³ Skeletal involvement in Gaucher disease includes bone pain, bone infarcts, and lytic lesions.

Whether splenectomy predisposes the patient to bone manifestations is controversial. Some believe that splenectomy decreases the total body reservoir for the storage of glycolipids and predisposes to their deposition in bone, which in turn results in cortical thinning, impaired remodeling, and decreased intraosseous blood flow, leading to osteonecrosis and fractures.⁴ This is more common in patients with type 1 Gaucher disease who have undergone splenectomy. (Types 2 and 3 are much rarer, occurring mainly in children; central nervous system involvement is a key feature. A discussion of these types is beyond the focus of this paper.) However, some studies suggest that the increase in bone manifestations after splenectomy may be simply because of severe disease.⁵ It should be noted that, since the advent of enzyme replacement therapy for Gaucher disease, splenectomy is now rarely performed.⁶

Anemia is also considered an independent risk factor for the development of avascular necrosis in type 1 Gaucher disease.⁷ Osteonecrosis due to Gaucher disease is relatively common in the femur, tibia, and humerus and uncommon in the ankle joints.⁸

Septic arthritis is unlikely in this patient in the absence of fever or signs of inflammation of the joint. Her long-standing history of ankle pain would also be unusual for infection, but a superimposed infectious process should always be suspected in an arthritic joint.

Avascular necrosis secondary to steroid use. Glucocorticoids are notorious for their adverse effects on bone. They induce osteocyte apoptosis and a decrease in bone remodeling, potentially predisposing to osteonecrosis.⁹ There is a high incidence of osteoporosis, osteonecrosis, and fracture risk with glucocorticoid therapy, and the incidence is dose-dependent. Discontinuation of the drug only partially restores fracture risk to baseline levels.^10,11

A meta-analysis of cohort studies with a total sample size of about 42,000 reported an increased risk of fracture at all ages with the use of glucocorticoids.¹² Because the minimum dosage and duration of therapy to prevent glucocorticoid-induced osteoporosis are not known, the only recommendation is to keep the dosage as low as possible.¹³

Glucocorticoid therapy is the most common cause of nontraumatic avascular necrosis. The risk of osteonecrosis in patients on long-term glucocorticoid therapy may be as high as 40%.¹⁴ The risk is increased with prolonged treatment and with high doses, but it can also occur with short-term exposure to high doses. The increased risk has been shown to persist for as long as 2 years after the drugs are discontinued.¹⁵ Glucocorticoid-induced bone disease commonly affects the hip and vertebrae.

At this stage of the workup, we cannot completely rule out glucocorticoid use as the cause. However, after considering this patient’s presentation and the key features of the other diagnoses, her ankle pain and back pain are more likely caused by her preexisting Gaucher disease.

CONTINUED EVALUATION


Initial laboratory tests (Table 1) reveal severe anemia and thrombocytopenia. Bone marrow biopsy of the iliac crest done as part of the workup for these conditions shows extensive bone marrow space replacement by histiocytic infiltrate, consistent with Gaucher disease. No other marrow process is observed.

Radiography of the ankle (Figure 1) shows a subtle lucency in the talar dome with minimal subarticular collapse seen on the lateral view, suggestive of avascular necrosis and diffuse osteopenia. Joint spaces are maintained.

Magnetic resonance imaging (MRI) of the ankle shows numerous bone infarcts with an approximately 15-mm region of mild articular surface collapse in the central and lateral aspect of the talar dome.

MRI of the back shows extensive abnormal bone marrow signal intensity throughout the spine, compatible with a marrow replacement process. Patchy nonexpansile T2/stir hyperintensity with serpiginous enhancement within the T9, T11, T12, L2, and L3 vertebral bodies as well as throughout the entire sacrum is consistent with bone infarct.

2. Based on the results of radiographic studies, which is most likely the immediate cause of her ankle pain?

• Talar avascular necrosis secondary to rheumatoid arthritis
• Talar avascular necrosis secondary to Gaucher disease
• Trauma-induced fracture of the talus
• Plantar fasciitis

Of the bones of the feet, the talus is unique. It is the second largest of the tarsal bones and does not have muscular or tendinous attachments. Sixty percent of the talus bone is covered by articular cartilage,¹⁶ so only a limited area is available for penetration of blood vessels. Also, small nutrient vessels and variations of intraosseous anastomoses with a lack of collateral circulation predispose the talus to osteonecrosis when the vascular supply is compromised.¹⁶

Radiographic evidence of avascular necrosis is the presence of bone that is more radiopaque than normal bone; this is necrotic bone surrounded by osteopenic bone. Avascular necrosis causes hyperemia and resorption of bone. The resorption does not take place in necrotic bone because of the lack of a vascular supply, and so it appears radiopaque, whereas the bone surrounding the necrotic bone becomes osteopenic and radiolucent.

The sclerotic rim of a bone infarct is also enhanced by an attempted healing process in which new bone forms on the surface of necrotic trabeculae, a process known as “creeping substitution.” This gives a typical sclerotic picture of the talus.

MRI is the most sensitive technique for detecting osteonecrosis. A characteristic radiographic pattern is seen with osteonecrosis of the talus starting with talar dome opacity, followed by deformity and, in severe cases, articular collapse and bone fragmentation.¹⁷

The radiograph in our patient’s case is not consistent with features of rheumatoid arthritis or traumatic fracture of the talus. In plantar fasciitis, radiographs are used to rule out other pathologies of the foot, and the only finding may be a bone spur seen at the site of pain. The bone spur is not the cause of pain in plantar fasciitis but may be a result of the plantar fasciitis itself.

Therefore, avascular necrosis secondary to Gaucher disease is most likely the immediate cause of her ankle pain.

THE COURSE OF TREATMENT

The patient is started on enzyme replacement therapy with taliglucerase alfa (see discussion of enzyme replacement below). For the ankle pain, conservative management is prescribed, with application of a splint and a boot.

After 4 months of conservative management, radiography (Figure 2) and magnetic resonance imaging (Figure 3) show progressive deterioration of the talus body, and her ankle pain has worsened. A 6-week trial of an ankle brace also proves futile. Her pain continues to worsen and is not controllable with high doses of pain medication. She requests below-the-knee amputation.

Given the complexity of this patient’s medical condition, fusion of the ankle and hindfoot—which in some patients is preferable to amputation—is not considered because of her extensive bone involvement and ongoing thrombocytopenia, which would impede healing after the procedure. Below-the-knee amputation is performed without complications.

Study of the specimen after amputation reveals talar bone necrosis and bone marrow infiltration by foamy macrophages, consistent with Gaucher disease (Figures 4–6).

GAUCHER DISEASE

Pharmacologic treatments, effective only for type 1 Gaucher disease, target hepatosplenomegaly, cytopenia, and bone manifestations. Two approaches are enzyme replacement therapy—ie, to replace the defective enzyme—and substrate reduction therapy—ie, to reduce the production and thus the accumulation of glucocerebroside. Enzyme replacement is the first choice of therapy; substrate reduction is reserved for patients unable to tolerate enzyme replacement therapy.

Enzyme replacement

Current drugs for enzyme replacement therapy are imiglucerase, taliglucerase alfa, and velaglucerase alfa. The drugs are given by intravenous infusion over 1 to 2 hours in an outpatient clinic or office every 2 weeks.

These drugs are extremely expensive. Currently, the estimated cost of therapy for 1 year would be $432,978 for imiglucerase, $324,870 for taliglucerase alfa, and $368,550 for velaglucerase alfa. (The estimated costs are for 1 year of treatment for a 70-kg patient at 60 U/kg every 2 weeks.)¹⁸ Taliglucerase alfa is less expensive than the other two because it is plant-derived and thus can be more readily produced on a large scale.¹⁹

Substrate reduction

Current drugs for substrate reduction therapy are eliglustat and miglustat. They are given orally. Eliglustat is the first oral drug approved as a first-line treatment for Gaucher disease.²⁰ Miglustat is approved only for mild to moderate disease when enzyme replacement fails or is not tolerated.

Patients can develop antibodies to any of the enzyme replacement drugs. It is not known whether this antibody response differs among the three drugs.²¹

Avascular necrosis of bone can occur in many clinical settings especially after a fracture, particularly of the head of the femur, which leads to interruption of blood supply to the area. Patients with sickle cell disease, those on corticosteroids or bisphosphonates (the latter causing osteonecrosis of the jaw), and those who have pancreatitis or human immunodeficiency virus infection are more prone to this bone complication.

In Gaucher disease, osteonecrosis is associated with splenectomy and severe disease and tends to occur at a younger age than in patients with other diagnoses.⁸ The plasma chitotriosidase activity and pulmonary and activation-regulated chemokines (PARC/CCL18), which are 10 to 40 times higher than normal in symptomatic patients with Gaucher disease, can be used as a biomarker of disease activity.⁸ Only plasma chitotriosidase is clinically available and used on a routine basis.

Bone involvement is seen in approximately 75% of the patients with type 1 Gaucher disease,²² and osteonecrosis is a severe form of bone involvement. Monitoring of patients for bone involvement is recommended. Enzyme replacement therapy for Gaucher disease needs to be started even if visceral disease is absent if the patient has evidence of bone involvement in the form of avascular necrosis.⁷ Prospective studies have shown that enzyme replacement therapy reduces the incidence of osteonecrosis.²³

FOLLOW-UP MANAGEMENT OF OUR PATIENT

Avascular necrosis in Gaucher disease more typically involves the hips and shoulders. In the case of our patient, the talus was the most affected bone. Other contributing factors may have been the use of steroids as a premedication (often unnecessary) for her enzyme replacement therapy, as well as the coexistent scleroderma.²⁴

The decision to switch from imiglucerase, to which she developed antibodies, to taliglucerase was made in the hope that the antibodies would not cross-react. After she started taliglucerase, her complete blood count values improved steadily. She did not require transfusions for more than 1 year. Her platelet count rose to 90 × 10⁹/L, and her hemoglobin to 12 g/dL.

A multidisciplinary approach with regular monitoring and appropriate initiation of therapy is necessary to prevent disastrous complications in patients with Gaucher disease.

A 54-year-old woman with a 1-month history of progressive weakness was transported to the emergency department of a local hospital when a family member found her unresponsive. Before this event, the patient had said she had been feeling tired and cold and looking pale for several weeks.

In the emergency department, her temperature was low. Cableomputed tomography (CT) of the head showed a 1.4-cm hyperdense extraaxial mass. Imaging of the chest showed focal consolidations within the anterior segment of the right upper lobe and the left and right lower lobes.

A urine toxicology screen was positive for acetaminophen (Tylenol), opiates, and benzodiazepines. She was given three doses of naloxone (Narcan), which raised her level of arousal; however, she later became obtunded again and was intubated and transferred to Cleveland Clinic.

A new CT scan of the head confirmed a small left temporal, extradural, calcified lesion with no mass effect or overt bleeding; it appeared most compatible with a solitary calcified meningioma—a likely benign finding.

Her medical history includes hypertension, type 2 diabetes (controlled with diet), and osteoarthritis of the spine. In 1999, she had undergone a hysterectomy that necessitated a blood transfusion. She has never smoked tobacco and does not consume alcohol or use illicit drugs. In the past she worked as a nurse’s aid in a nursing home. However, for the past several years she has stayed at home. Her only avocation of note is gardening.

Initial physical examination

The patient is intubated and sedated. Her temperature is 35.3°C (95.5°F), blood pressure 122/81 mm Hg, heart rate 83 beats per minute, and respiratory rate 14 on assist-controlled ventilator settings with an Fio₂ of 100% and a positive end-expiratory pressure of 5 cm H₂O.

Her pupils are round, equal, and reactive to light. Her face is symmetric and notable for hirsutism over the chin. Her neck is supple and without lymphadenopathy or thyromegaly.

Rhonchi can be heard at both lung bases. She has normal bowel sounds, and her abdomen is soft and nondistended, with no masses or palpable hepatosplenomegaly. She has no pedal edema on either side, and no clubbing or cyanosis. Her skin is intact, without rashes, lesions, or tattoos. She is able to withdraw from painful stimuli in all four extremities.

INITIAL TESTS PROVIDE A CLUE

1. Which of the following is the likely cause of this patient’s pancytopenia?

• Folate deficiency
• Gastrointestinal bleeding secondary to colon cancer
• 
  Acute myeloid leukemia
• Paroxysmal nocturnal hemoglobinuria
• Myelophthisis
• Other

Causes of pancytopenia are listed in Table 2.

Folate deficiency

Folate is necessary for thymidylate synthesis, a rate-limiting step in DNA synthesis. The minimum daily requirement for dietary folate intake is 50 μg.

Severe deficiency of folate has been reported to cause pancytopenia in alcoholics.¹ Abuse of alcohol leads to an abrupt decrease in serum folate (within 2 to 4 days of ceasing intake of proper amounts of folate, as in an alcoholic binge) by inhibiting its absorption in the proximal jejunum as well as its metabolism in the liver.² The resulting folate deficiency, if sustained, can develop into megaloblastosis in 5 to 10 weeks.

The duration of weakness and pallor reported by this patient would raise suspicion of folate deficiency if she had a history of malnutrition or of alcohol abuse, but she has neither. Further, her mean corpuscular volume is 82.5 fL, red blood cell folate 391 ng/mL (reference range 257–800 ng/mL), and serum vitamin B₁₂ 1,886 pg/mL (22–700 pg/mL), and she has no macro-ovalocytes or hypersegmented neutrophils on a peripheral blood smear. This makes folate or vitamin B₁₂ deficiency less likely.

Gastrointestinal bleeding due to colon cancer

Iron-deficiency anemia, hematochezia, melena, a change in bowel habits, and abdominal pain may be manifestations of colon cancer. Cancers of the colon originate from adenomatous polyps arising from the colonic mucosa.

The quantity of occult blood loss depends on the site of the tumor. Patients with tumors in the cecum or ascending colon lose an average of 9 mL/day, whereas those with tumors in the transverse, descending, or sigmoid colon or rectum lose less than 2 mL/day.³

Pertinent laboratory findings in iron-deficiency anemia are a low iron concentration, a low transferrin saturation, a depleted serum ferritin, and a normal to high total iron-binding capacity. An initial microcytic normochromic anemia eventually progresses to a microcytic hypochromic anemia that has a tendency to increasingly demonstrate anisocytosis and poikilocytosis.

Our patient’s symptoms, signs, and laboratory values (with normocytic normochromic anemia) are inconsistent with symptomatic colon cancer leading to iron-deficiency anemia.

Acute myeloid leukemia generally manifests with symptoms related to pancytopenia, with weakness and fatigability being the most common.⁴

In this condition, genetic alterations in hematopoietic precursor cells result in reduced differentiation capacity and accumulation of leukemic blasts in the bone marrow, peripheral blood, and other tissues.

Peripheral blood analysis usually reveals normocytic normochromic anemia with blasts. To establish a diagnosis of acute myeloid leukemia, one must observe at least 20% myeloblasts in the blood, the bone marrow, or both.

No blasts are seen on our patient’s peripheral blood smear, making acute myeloid leukemia less likely.

Paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria is a possibility in the setting of intravascular hemolytic anemia, bone marrow failure, and thrombosis.

These processes are due to a defect in the glycosyl phosphatidyl inositol (GPI) anchor caused by an abnormality in the PIG-A gene. Partial or complete absence of the GPI anchor allows for activation of complement-mediated hemolysis. A diminished rate of hematopoiesis is presumably responsible for reticulocytopenia, granulocytopenia, or thrombocytopenia, though reticulocytosis can also be seen.^5,6 The highly thrombogenic state is believed to occur because of microparticles rich in phosphatidylserine.⁷

Our patient’s peripheral smear has rare fragmented red blood cells and lacks teardrop red cells. Although paroxysmal nocturnal hemoglobinuria does not have characteristic morphologic features in the peripheral blood, there are no signs of thrombosis in our patient. Her lactate dehydrogenase level is 395 U/L (reference range 100–220 U/L), and her haptoglobin level is less than 20 mg/dL (33–246). These findings could indicate a low level of intravascular hemolysis.

Myelophthisis

Myelophthisis refers to any disorder in which an abnormal cell process invades the bone marrow, damaging hematopoietic tissue. These processes include neoplastic diseases, storage disorders, and a variety of infections. A decrease in all three cell types may result, depending on the severity of invasion. Documented infectious causes include hepatitis viruses, Epstein-Barr virus, human immunodeficiency virus (HIV), mycobacteria, and fungi.

Our patient’s condition is likely due to a marrow-based process of uncertain etiology. In myelophthisic processes, one may see teardrop red cells, which are not seen in this patient’s smear. However, on her chest imaging, the finding of focal consolidations within the anterior segment of the right upper lobe and both lower lobes raises suspicion of an infectious cause.

CASE CONTINUED: SHE UNDERGOES DIAGNOSTIC TESTING

Let us recap some of the laboratory studies that document the extent of our patient’s pancytopenia and the pattern of her anemia:

• Hemoglobin 10.2 g/dL (reference range 11.5–15.5 g/dL)
• Platelet count 27 × 10⁹/L (150–400)
• Leukopenia with profound T-cell lymphopenia
• Iron 59 μg/dL (30–140)
• Total iron-binding capacity 110 μg/dL (210–415)
• Ferritin 3,004 ng/mL (18–300)
• Transferrin saturation 54% (11%–46%).

2. Which of the following would be the best test to obtain next?

• Bone marrow examination
• Blood cultures
• Tuberculin skin test
• Liver biopsy
• Positron emission tomography and CT

Our patient has unexplained pancytopenia. While all the tests listed above might shed light on her condition, a bone marrow examination would be the best test to obtain next.

Urine histoplasma antigen studies are positive at greater than 39 ng/mL (normal 0, low positive < 0.6–3.9, moderate positive 4.0–19.9, high positive 20–39 ng/mL). A culture of the marrow subsequently grows this organism.

3. Which of the following tests would establish a definitive diagnosis in this patient?

• Methenamine silver stain of the marrow
• Serum antibody testing
• Fungal culture
• Peripheral blood smear
• Carbolfuchsin stain of marrow
• Urine histoplasma antigen

A prompt diagnosis is critical in patients with acute pulmonary histoplasmosis or progressive disseminated histoplasmosis because early treatment may shorten the clinical course and length of treatment and, in cases of disseminated histoplasmosis, prevent death.^8–10

Histopathologic examination of the bone marrow gives the most rapid results, although biopsy to obtain the tissue is invasive. It can give a definitive diagnosis if it reveals the typical 2- to 4-μm yeast structures of H capsulatum. These are observed on an aspirate smear of the patient’s bone marrow biopsy (Figure 1) and can be confirmed by methenamine silver or periodic acid-Schiff staining of the tissue.

Antibody detection is less practical because the antibodies take 2 to 6 weeks after infection to form.¹¹ Also, it is less useful in cases of disseminated infection because many of these patients are immunosuppressed.

Fungal culture remains the gold standard diagnostic test for histoplasmosis. However, results may take up to 1 month and may be falsely negative in less severe cases.

Histoplasma antigen testing is of greater utility in patients with severe disease, including cases of disseminated histoplasmosis. Rates of antigen detection approach 90% in urine specimens from non-AIDS patients with disseminated infection.¹² The urine assay has a greater sensitivity and specificity than the serum assay. The rate of detection is lower (ie, around 82%) in patients with acute pulmonary histoplasmosis when both the serum and urine specimens are tested.¹³

The immunoassay for histoplasma antigen is particularly useful for monitoring the response to therapy. Antigen levels should be measured before treatment is started and at 2 weeks, 1 month, and then approximately every 3 months during therapy.¹⁴ If the treatment is effective, antigens should decline by at least 20% in the first month of treatment and by another 20% in each of the following 3-month intervals. Antigen testing should be done every 3 months until a negative antigen level is achieved. The antigen level should also be followed for at least 6 months after treatment has stopped.¹⁴

HISTOPLASMA IS INHALED

H capsulatum is the cause of one of the most common pulmonary and systemic mycotic infections in the world, with hundreds of thousands of new cases annually. In areas where the soil is contaminated by bird or bat guano, the fungus is inhaled, resulting in an asymptomatic or a self-limiting influenza-like syndrome in an immunocompetent individual.¹⁵

An antigen-specific CD4⁺ T lymphocytemediated immunity occurs. The immune response of the host is thought to be fungistatic rather than fungicidal, resulting in a persistent inactive infection capable of reactivation in the presence of a host-pathogen imbalance.¹⁶

Most infections are asymptomatic or self-limited. For every 2,000 acute infections there is one that results in severe and progressive dissemination, usually in an immunocompromised host.^17,18

TREATMENT OF HISTOPLASMOSIS

4. What is the appropriate initial choice of treatment for a severe case of disseminated histoplasmosis?

• Amphotericin B in a lipid complex formulation (Abelcet)
• Itraconazole (Sporanox)
• Fluconazole (Diflucan)
• Ketoconazole (Nizoral)

Untreated, acute disseminated histoplasmosis can progress over a period of 2 to 12 weeks, ultimately killing the patient.^17,19

The leading therapies include amphotericin B in a lipid formulation and azole drugs, in particular itraconazole. Fluconazole and ketoconazole are not first-line options in severe cases because they are less predictably effective, and ketoconazole has a higher rate of side effects.^20–23 The current recommendation is to treat severely ill hospitalized patients with one of the liposomal formulations or the lipid complex formulation of amphotericin B. Itraconazole is used for patients who have mild to moderate symptoms and as a step-down therapy in patients who improve after initial use of amphotericin B.

CASE CONCLUDED: THE PATIENT RECOVERS

At the time of the initial patient encounter, there was no history of or obvious cause of immunosuppression in this patient. She was found to be HIV-negative and was subsequently diagnosed with “profound immunosuppression of unknown etiology” resulting in a low CD4 count.

The patient receives trimethoprim-sulfamethoxazole (Bactrim, Septra) and azithromycin (Zithromax) for prophylaxis against Pneumocystis carinii pneumonia and Mycobacterium avium intracellulare infection. Two months after the hospitalization, she recalls being at a corn maze 1 month before becoming ill.

A 54-year-old woman with a 1-month history of progressive weakness was transported to the emergency department of a local hospital when a family member found her unresponsive. Before this event, the patient had said she had been feeling tired and cold and looking pale for several weeks.

In the emergency department, her temperature was low. Cableomputed tomography (CT) of the head showed a 1.4-cm hyperdense extraaxial mass. Imaging of the chest showed focal consolidations within the anterior segment of the right upper lobe and the left and right lower lobes.

A urine toxicology screen was positive for acetaminophen (Tylenol), opiates, and benzodiazepines. She was given three doses of naloxone (Narcan), which raised her level of arousal; however, she later became obtunded again and was intubated and transferred to Cleveland Clinic.

A new CT scan of the head confirmed a small left temporal, extradural, calcified lesion with no mass effect or overt bleeding; it appeared most compatible with a solitary calcified meningioma—a likely benign finding.

Her medical history includes hypertension, type 2 diabetes (controlled with diet), and osteoarthritis of the spine. In 1999, she had undergone a hysterectomy that necessitated a blood transfusion. She has never smoked tobacco and does not consume alcohol or use illicit drugs. In the past she worked as a nurse’s aid in a nursing home. However, for the past several years she has stayed at home. Her only avocation of note is gardening.

Initial physical examination

The patient is intubated and sedated. Her temperature is 35.3°C (95.5°F), blood pressure 122/81 mm Hg, heart rate 83 beats per minute, and respiratory rate 14 on assist-controlled ventilator settings with an Fio₂ of 100% and a positive end-expiratory pressure of 5 cm H₂O.

Her pupils are round, equal, and reactive to light. Her face is symmetric and notable for hirsutism over the chin. Her neck is supple and without lymphadenopathy or thyromegaly.

Rhonchi can be heard at both lung bases. She has normal bowel sounds, and her abdomen is soft and nondistended, with no masses or palpable hepatosplenomegaly. She has no pedal edema on either side, and no clubbing or cyanosis. Her skin is intact, without rashes, lesions, or tattoos. She is able to withdraw from painful stimuli in all four extremities.

INITIAL TESTS PROVIDE A CLUE

1. Which of the following is the likely cause of this patient’s pancytopenia?

• Folate deficiency
• Gastrointestinal bleeding secondary to colon cancer
• 
  Acute myeloid leukemia
• Paroxysmal nocturnal hemoglobinuria
• Myelophthisis
• Other

Causes of pancytopenia are listed in Table 2.

Folate deficiency

Folate is necessary for thymidylate synthesis, a rate-limiting step in DNA synthesis. The minimum daily requirement for dietary folate intake is 50 μg.

Severe deficiency of folate has been reported to cause pancytopenia in alcoholics.¹ Abuse of alcohol leads to an abrupt decrease in serum folate (within 2 to 4 days of ceasing intake of proper amounts of folate, as in an alcoholic binge) by inhibiting its absorption in the proximal jejunum as well as its metabolism in the liver.² The resulting folate deficiency, if sustained, can develop into megaloblastosis in 5 to 10 weeks.

The duration of weakness and pallor reported by this patient would raise suspicion of folate deficiency if she had a history of malnutrition or of alcohol abuse, but she has neither. Further, her mean corpuscular volume is 82.5 fL, red blood cell folate 391 ng/mL (reference range 257–800 ng/mL), and serum vitamin B₁₂ 1,886 pg/mL (22–700 pg/mL), and she has no macro-ovalocytes or hypersegmented neutrophils on a peripheral blood smear. This makes folate or vitamin B₁₂ deficiency less likely.

Gastrointestinal bleeding due to colon cancer

Iron-deficiency anemia, hematochezia, melena, a change in bowel habits, and abdominal pain may be manifestations of colon cancer. Cancers of the colon originate from adenomatous polyps arising from the colonic mucosa.

The quantity of occult blood loss depends on the site of the tumor. Patients with tumors in the cecum or ascending colon lose an average of 9 mL/day, whereas those with tumors in the transverse, descending, or sigmoid colon or rectum lose less than 2 mL/day.³

Pertinent laboratory findings in iron-deficiency anemia are a low iron concentration, a low transferrin saturation, a depleted serum ferritin, and a normal to high total iron-binding capacity. An initial microcytic normochromic anemia eventually progresses to a microcytic hypochromic anemia that has a tendency to increasingly demonstrate anisocytosis and poikilocytosis.

Our patient’s symptoms, signs, and laboratory values (with normocytic normochromic anemia) are inconsistent with symptomatic colon cancer leading to iron-deficiency anemia.

Acute myeloid leukemia generally manifests with symptoms related to pancytopenia, with weakness and fatigability being the most common.⁴

In this condition, genetic alterations in hematopoietic precursor cells result in reduced differentiation capacity and accumulation of leukemic blasts in the bone marrow, peripheral blood, and other tissues.

Peripheral blood analysis usually reveals normocytic normochromic anemia with blasts. To establish a diagnosis of acute myeloid leukemia, one must observe at least 20% myeloblasts in the blood, the bone marrow, or both.

No blasts are seen on our patient’s peripheral blood smear, making acute myeloid leukemia less likely.

Paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria is a possibility in the setting of intravascular hemolytic anemia, bone marrow failure, and thrombosis.

These processes are due to a defect in the glycosyl phosphatidyl inositol (GPI) anchor caused by an abnormality in the PIG-A gene. Partial or complete absence of the GPI anchor allows for activation of complement-mediated hemolysis. A diminished rate of hematopoiesis is presumably responsible for reticulocytopenia, granulocytopenia, or thrombocytopenia, though reticulocytosis can also be seen.^5,6 The highly thrombogenic state is believed to occur because of microparticles rich in phosphatidylserine.⁷

Our patient’s peripheral smear has rare fragmented red blood cells and lacks teardrop red cells. Although paroxysmal nocturnal hemoglobinuria does not have characteristic morphologic features in the peripheral blood, there are no signs of thrombosis in our patient. Her lactate dehydrogenase level is 395 U/L (reference range 100–220 U/L), and her haptoglobin level is less than 20 mg/dL (33–246). These findings could indicate a low level of intravascular hemolysis.

Myelophthisis

Myelophthisis refers to any disorder in which an abnormal cell process invades the bone marrow, damaging hematopoietic tissue. These processes include neoplastic diseases, storage disorders, and a variety of infections. A decrease in all three cell types may result, depending on the severity of invasion. Documented infectious causes include hepatitis viruses, Epstein-Barr virus, human immunodeficiency virus (HIV), mycobacteria, and fungi.

Our patient’s condition is likely due to a marrow-based process of uncertain etiology. In myelophthisic processes, one may see teardrop red cells, which are not seen in this patient’s smear. However, on her chest imaging, the finding of focal consolidations within the anterior segment of the right upper lobe and both lower lobes raises suspicion of an infectious cause.

CASE CONTINUED: SHE UNDERGOES DIAGNOSTIC TESTING

Let us recap some of the laboratory studies that document the extent of our patient’s pancytopenia and the pattern of her anemia:

• Hemoglobin 10.2 g/dL (reference range 11.5–15.5 g/dL)
• Platelet count 27 × 10⁹/L (150–400)
• Leukopenia with profound T-cell lymphopenia
• Iron 59 μg/dL (30–140)
• Total iron-binding capacity 110 μg/dL (210–415)
• Ferritin 3,004 ng/mL (18–300)
• Transferrin saturation 54% (11%–46%).

2. Which of the following would be the best test to obtain next?

• Bone marrow examination
• Blood cultures
• Tuberculin skin test
• Liver biopsy
• Positron emission tomography and CT

Our patient has unexplained pancytopenia. While all the tests listed above might shed light on her condition, a bone marrow examination would be the best test to obtain next.

Urine histoplasma antigen studies are positive at greater than 39 ng/mL (normal 0, low positive < 0.6–3.9, moderate positive 4.0–19.9, high positive 20–39 ng/mL). A culture of the marrow subsequently grows this organism.

3. Which of the following tests would establish a definitive diagnosis in this patient?

• Methenamine silver stain of the marrow
• Serum antibody testing
• Fungal culture
• Peripheral blood smear
• Carbolfuchsin stain of marrow
• Urine histoplasma antigen

A prompt diagnosis is critical in patients with acute pulmonary histoplasmosis or progressive disseminated histoplasmosis because early treatment may shorten the clinical course and length of treatment and, in cases of disseminated histoplasmosis, prevent death.^8–10

Histopathologic examination of the bone marrow gives the most rapid results, although biopsy to obtain the tissue is invasive. It can give a definitive diagnosis if it reveals the typical 2- to 4-μm yeast structures of H capsulatum. These are observed on an aspirate smear of the patient’s bone marrow biopsy (Figure 1) and can be confirmed by methenamine silver or periodic acid-Schiff staining of the tissue.

Antibody detection is less practical because the antibodies take 2 to 6 weeks after infection to form.¹¹ Also, it is less useful in cases of disseminated infection because many of these patients are immunosuppressed.

Fungal culture remains the gold standard diagnostic test for histoplasmosis. However, results may take up to 1 month and may be falsely negative in less severe cases.

Histoplasma antigen testing is of greater utility in patients with severe disease, including cases of disseminated histoplasmosis. Rates of antigen detection approach 90% in urine specimens from non-AIDS patients with disseminated infection.¹² The urine assay has a greater sensitivity and specificity than the serum assay. The rate of detection is lower (ie, around 82%) in patients with acute pulmonary histoplasmosis when both the serum and urine specimens are tested.¹³

The immunoassay for histoplasma antigen is particularly useful for monitoring the response to therapy. Antigen levels should be measured before treatment is started and at 2 weeks, 1 month, and then approximately every 3 months during therapy.¹⁴ If the treatment is effective, antigens should decline by at least 20% in the first month of treatment and by another 20% in each of the following 3-month intervals. Antigen testing should be done every 3 months until a negative antigen level is achieved. The antigen level should also be followed for at least 6 months after treatment has stopped.¹⁴

HISTOPLASMA IS INHALED

H capsulatum is the cause of one of the most common pulmonary and systemic mycotic infections in the world, with hundreds of thousands of new cases annually. In areas where the soil is contaminated by bird or bat guano, the fungus is inhaled, resulting in an asymptomatic or a self-limiting influenza-like syndrome in an immunocompetent individual.¹⁵

An antigen-specific CD4⁺ T lymphocytemediated immunity occurs. The immune response of the host is thought to be fungistatic rather than fungicidal, resulting in a persistent inactive infection capable of reactivation in the presence of a host-pathogen imbalance.¹⁶

Most infections are asymptomatic or self-limited. For every 2,000 acute infections there is one that results in severe and progressive dissemination, usually in an immunocompromised host.^17,18

TREATMENT OF HISTOPLASMOSIS

4. What is the appropriate initial choice of treatment for a severe case of disseminated histoplasmosis?

• Amphotericin B in a lipid complex formulation (Abelcet)
• Itraconazole (Sporanox)
• Fluconazole (Diflucan)
• Ketoconazole (Nizoral)

Untreated, acute disseminated histoplasmosis can progress over a period of 2 to 12 weeks, ultimately killing the patient.^17,19

The leading therapies include amphotericin B in a lipid formulation and azole drugs, in particular itraconazole. Fluconazole and ketoconazole are not first-line options in severe cases because they are less predictably effective, and ketoconazole has a higher rate of side effects.^20–23 The current recommendation is to treat severely ill hospitalized patients with one of the liposomal formulations or the lipid complex formulation of amphotericin B. Itraconazole is used for patients who have mild to moderate symptoms and as a step-down therapy in patients who improve after initial use of amphotericin B.

CASE CONCLUDED: THE PATIENT RECOVERS

At the time of the initial patient encounter, there was no history of or obvious cause of immunosuppression in this patient. She was found to be HIV-negative and was subsequently diagnosed with “profound immunosuppression of unknown etiology” resulting in a low CD4 count.

The patient receives trimethoprim-sulfamethoxazole (Bactrim, Septra) and azithromycin (Zithromax) for prophylaxis against Pneumocystis carinii pneumonia and Mycobacterium avium intracellulare infection. Two months after the hospitalization, she recalls being at a corn maze 1 month before becoming ill.

A 54-year-old woman with a 1-month history of progressive weakness was transported to the emergency department of a local hospital when a family member found her unresponsive. Before this event, the patient had said she had been feeling tired and cold and looking pale for several weeks.

In the emergency department, her temperature was low. Cableomputed tomography (CT) of the head showed a 1.4-cm hyperdense extraaxial mass. Imaging of the chest showed focal consolidations within the anterior segment of the right upper lobe and the left and right lower lobes.

A urine toxicology screen was positive for acetaminophen (Tylenol), opiates, and benzodiazepines. She was given three doses of naloxone (Narcan), which raised her level of arousal; however, she later became obtunded again and was intubated and transferred to Cleveland Clinic.

A new CT scan of the head confirmed a small left temporal, extradural, calcified lesion with no mass effect or overt bleeding; it appeared most compatible with a solitary calcified meningioma—a likely benign finding.

Her medical history includes hypertension, type 2 diabetes (controlled with diet), and osteoarthritis of the spine. In 1999, she had undergone a hysterectomy that necessitated a blood transfusion. She has never smoked tobacco and does not consume alcohol or use illicit drugs. In the past she worked as a nurse’s aid in a nursing home. However, for the past several years she has stayed at home. Her only avocation of note is gardening.

Initial physical examination

The patient is intubated and sedated. Her temperature is 35.3°C (95.5°F), blood pressure 122/81 mm Hg, heart rate 83 beats per minute, and respiratory rate 14 on assist-controlled ventilator settings with an Fio₂ of 100% and a positive end-expiratory pressure of 5 cm H₂O.

Her pupils are round, equal, and reactive to light. Her face is symmetric and notable for hirsutism over the chin. Her neck is supple and without lymphadenopathy or thyromegaly.

Rhonchi can be heard at both lung bases. She has normal bowel sounds, and her abdomen is soft and nondistended, with no masses or palpable hepatosplenomegaly. She has no pedal edema on either side, and no clubbing or cyanosis. Her skin is intact, without rashes, lesions, or tattoos. She is able to withdraw from painful stimuli in all four extremities.

INITIAL TESTS PROVIDE A CLUE

1. Which of the following is the likely cause of this patient’s pancytopenia?

• Folate deficiency
• Gastrointestinal bleeding secondary to colon cancer
• 
  Acute myeloid leukemia
• Paroxysmal nocturnal hemoglobinuria
• Myelophthisis
• Other

Causes of pancytopenia are listed in Table 2.

Folate deficiency

Folate is necessary for thymidylate synthesis, a rate-limiting step in DNA synthesis. The minimum daily requirement for dietary folate intake is 50 μg.

Severe deficiency of folate has been reported to cause pancytopenia in alcoholics.¹ Abuse of alcohol leads to an abrupt decrease in serum folate (within 2 to 4 days of ceasing intake of proper amounts of folate, as in an alcoholic binge) by inhibiting its absorption in the proximal jejunum as well as its metabolism in the liver.² The resulting folate deficiency, if sustained, can develop into megaloblastosis in 5 to 10 weeks.

The duration of weakness and pallor reported by this patient would raise suspicion of folate deficiency if she had a history of malnutrition or of alcohol abuse, but she has neither. Further, her mean corpuscular volume is 82.5 fL, red blood cell folate 391 ng/mL (reference range 257–800 ng/mL), and serum vitamin B₁₂ 1,886 pg/mL (22–700 pg/mL), and she has no macro-ovalocytes or hypersegmented neutrophils on a peripheral blood smear. This makes folate or vitamin B₁₂ deficiency less likely.

Gastrointestinal bleeding due to colon cancer

Iron-deficiency anemia, hematochezia, melena, a change in bowel habits, and abdominal pain may be manifestations of colon cancer. Cancers of the colon originate from adenomatous polyps arising from the colonic mucosa.

The quantity of occult blood loss depends on the site of the tumor. Patients with tumors in the cecum or ascending colon lose an average of 9 mL/day, whereas those with tumors in the transverse, descending, or sigmoid colon or rectum lose less than 2 mL/day.³

Pertinent laboratory findings in iron-deficiency anemia are a low iron concentration, a low transferrin saturation, a depleted serum ferritin, and a normal to high total iron-binding capacity. An initial microcytic normochromic anemia eventually progresses to a microcytic hypochromic anemia that has a tendency to increasingly demonstrate anisocytosis and poikilocytosis.

Our patient’s symptoms, signs, and laboratory values (with normocytic normochromic anemia) are inconsistent with symptomatic colon cancer leading to iron-deficiency anemia.

Acute myeloid leukemia generally manifests with symptoms related to pancytopenia, with weakness and fatigability being the most common.⁴

In this condition, genetic alterations in hematopoietic precursor cells result in reduced differentiation capacity and accumulation of leukemic blasts in the bone marrow, peripheral blood, and other tissues.

Peripheral blood analysis usually reveals normocytic normochromic anemia with blasts. To establish a diagnosis of acute myeloid leukemia, one must observe at least 20% myeloblasts in the blood, the bone marrow, or both.

No blasts are seen on our patient’s peripheral blood smear, making acute myeloid leukemia less likely.

Paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria is a possibility in the setting of intravascular hemolytic anemia, bone marrow failure, and thrombosis.

These processes are due to a defect in the glycosyl phosphatidyl inositol (GPI) anchor caused by an abnormality in the PIG-A gene. Partial or complete absence of the GPI anchor allows for activation of complement-mediated hemolysis. A diminished rate of hematopoiesis is presumably responsible for reticulocytopenia, granulocytopenia, or thrombocytopenia, though reticulocytosis can also be seen.^5,6 The highly thrombogenic state is believed to occur because of microparticles rich in phosphatidylserine.⁷

Our patient’s peripheral smear has rare fragmented red blood cells and lacks teardrop red cells. Although paroxysmal nocturnal hemoglobinuria does not have characteristic morphologic features in the peripheral blood, there are no signs of thrombosis in our patient. Her lactate dehydrogenase level is 395 U/L (reference range 100–220 U/L), and her haptoglobin level is less than 20 mg/dL (33–246). These findings could indicate a low level of intravascular hemolysis.

Myelophthisis

Myelophthisis refers to any disorder in which an abnormal cell process invades the bone marrow, damaging hematopoietic tissue. These processes include neoplastic diseases, storage disorders, and a variety of infections. A decrease in all three cell types may result, depending on the severity of invasion. Documented infectious causes include hepatitis viruses, Epstein-Barr virus, human immunodeficiency virus (HIV), mycobacteria, and fungi.

Our patient’s condition is likely due to a marrow-based process of uncertain etiology. In myelophthisic processes, one may see teardrop red cells, which are not seen in this patient’s smear. However, on her chest imaging, the finding of focal consolidations within the anterior segment of the right upper lobe and both lower lobes raises suspicion of an infectious cause.

CASE CONTINUED: SHE UNDERGOES DIAGNOSTIC TESTING

Let us recap some of the laboratory studies that document the extent of our patient’s pancytopenia and the pattern of her anemia:

• Hemoglobin 10.2 g/dL (reference range 11.5–15.5 g/dL)
• Platelet count 27 × 10⁹/L (150–400)
• Leukopenia with profound T-cell lymphopenia
• Iron 59 μg/dL (30–140)
• Total iron-binding capacity 110 μg/dL (210–415)
• Ferritin 3,004 ng/mL (18–300)
• Transferrin saturation 54% (11%–46%).

2. Which of the following would be the best test to obtain next?

• Bone marrow examination
• Blood cultures
• Tuberculin skin test
• Liver biopsy
• Positron emission tomography and CT

Our patient has unexplained pancytopenia. While all the tests listed above might shed light on her condition, a bone marrow examination would be the best test to obtain next.

Urine histoplasma antigen studies are positive at greater than 39 ng/mL (normal 0, low positive < 0.6–3.9, moderate positive 4.0–19.9, high positive 20–39 ng/mL). A culture of the marrow subsequently grows this organism.

3. Which of the following tests would establish a definitive diagnosis in this patient?

• Methenamine silver stain of the marrow
• Serum antibody testing
• Fungal culture
• Peripheral blood smear
• Carbolfuchsin stain of marrow
• Urine histoplasma antigen

A prompt diagnosis is critical in patients with acute pulmonary histoplasmosis or progressive disseminated histoplasmosis because early treatment may shorten the clinical course and length of treatment and, in cases of disseminated histoplasmosis, prevent death.^8–10

Histopathologic examination of the bone marrow gives the most rapid results, although biopsy to obtain the tissue is invasive. It can give a definitive diagnosis if it reveals the typical 2- to 4-μm yeast structures of H capsulatum. These are observed on an aspirate smear of the patient’s bone marrow biopsy (Figure 1) and can be confirmed by methenamine silver or periodic acid-Schiff staining of the tissue.

Antibody detection is less practical because the antibodies take 2 to 6 weeks after infection to form.¹¹ Also, it is less useful in cases of disseminated infection because many of these patients are immunosuppressed.

Fungal culture remains the gold standard diagnostic test for histoplasmosis. However, results may take up to 1 month and may be falsely negative in less severe cases.

Histoplasma antigen testing is of greater utility in patients with severe disease, including cases of disseminated histoplasmosis. Rates of antigen detection approach 90% in urine specimens from non-AIDS patients with disseminated infection.¹² The urine assay has a greater sensitivity and specificity than the serum assay. The rate of detection is lower (ie, around 82%) in patients with acute pulmonary histoplasmosis when both the serum and urine specimens are tested.¹³

The immunoassay for histoplasma antigen is particularly useful for monitoring the response to therapy. Antigen levels should be measured before treatment is started and at 2 weeks, 1 month, and then approximately every 3 months during therapy.¹⁴ If the treatment is effective, antigens should decline by at least 20% in the first month of treatment and by another 20% in each of the following 3-month intervals. Antigen testing should be done every 3 months until a negative antigen level is achieved. The antigen level should also be followed for at least 6 months after treatment has stopped.¹⁴

HISTOPLASMA IS INHALED

H capsulatum is the cause of one of the most common pulmonary and systemic mycotic infections in the world, with hundreds of thousands of new cases annually. In areas where the soil is contaminated by bird or bat guano, the fungus is inhaled, resulting in an asymptomatic or a self-limiting influenza-like syndrome in an immunocompetent individual.¹⁵

An antigen-specific CD4⁺ T lymphocytemediated immunity occurs. The immune response of the host is thought to be fungistatic rather than fungicidal, resulting in a persistent inactive infection capable of reactivation in the presence of a host-pathogen imbalance.¹⁶

Most infections are asymptomatic or self-limited. For every 2,000 acute infections there is one that results in severe and progressive dissemination, usually in an immunocompromised host.^17,18

TREATMENT OF HISTOPLASMOSIS

4. What is the appropriate initial choice of treatment for a severe case of disseminated histoplasmosis?

• Amphotericin B in a lipid complex formulation (Abelcet)
• Itraconazole (Sporanox)
• Fluconazole (Diflucan)
• Ketoconazole (Nizoral)

Untreated, acute disseminated histoplasmosis can progress over a period of 2 to 12 weeks, ultimately killing the patient.^17,19

The leading therapies include amphotericin B in a lipid formulation and azole drugs, in particular itraconazole. Fluconazole and ketoconazole are not first-line options in severe cases because they are less predictably effective, and ketoconazole has a higher rate of side effects.^20–23 The current recommendation is to treat severely ill hospitalized patients with one of the liposomal formulations or the lipid complex formulation of amphotericin B. Itraconazole is used for patients who have mild to moderate symptoms and as a step-down therapy in patients who improve after initial use of amphotericin B.

CASE CONCLUDED: THE PATIENT RECOVERS

At the time of the initial patient encounter, there was no history of or obvious cause of immunosuppression in this patient. She was found to be HIV-negative and was subsequently diagnosed with “profound immunosuppression of unknown etiology” resulting in a low CD4 count.

The patient receives trimethoprim-sulfamethoxazole (Bactrim, Septra) and azithromycin (Zithromax) for prophylaxis against Pneumocystis carinii pneumonia and Mycobacterium avium intracellulare infection. Two months after the hospitalization, she recalls being at a corn maze 1 month before becoming ill.