The Journal of Family Practice

THE CASE

A 23-year-old immunocompetent woman was referred to our spinal clinic with a 6-month history of low back pain that radiated to her right flank, buttock, and groin. She’d had intermittent urinary problems, including mild dysuria and frequency, and had been treated with antibiotics for a presumed urinary tract infection on 3 previous occasions, but her pain gradually increased and eventually became constant.

The patient had no history of fever, malaise, or weight loss. She denied consuming unpasteurized milk or undercooked poultry, and hadn’t recently experienced diarrhea or vomiting.

Eight years earlier, she had undergone anterior fusion of her spine for idiopathic scoliosis. At that time, she was at Risser grade 1, and her Cobb angle was 50°; metallic instrumentation was implanted at T10 to L3 to prevent progression of the scoliosis. Her recovery had been uneventful.

During examination, her temperature, pulse, respiratory rate, blood pressure, and nervous system were all normal. Her hips appeared normal, as well, and a straight leg raise was negative bilaterally. The patient had mild midline lumbar tenderness. Spinal range of movement revealed decreased flexion and mild pain.

X-rays (FIGURE 1) showed no changes in the previous metalwork in her spine. There was decreased disk height at the L3/4 level, but no significant bony erosion or soft-tissue shadows. Laboratory testing revealed a C-reactive protein (CRP) level of 240 mg/dL (normal, <1 mg/dL) and her erythrocyte sedimentation rate (ESR) was 102 mm/h—more than 5 times higher than it should have been.¹ The patient had a normal peripheral white cell count (WCC). Midstream urine cultures were negative.


The patient was admitted to the hospital for further work-up. Magnetic resonance imaging (MRI) of the lumbar spine showed gross abnormality at the L3-L4 disk level with erosion of the end plates, fluid in the disk space, marked enhancing edema, and mild surrounding soft-tissue edematous changes, but no evidence of any epidural abscess (FIGURE 2). The patient had a fluoroscopy-guided needle biopsy of the disk on the same day and received intravenous (IV) ceftriaxone 2 g twice a day. Blood and urine cultures were negative.

THE DIAGNOSIS

We suspected our patient had spondylodiscitis, an infection of the spine that includes spondylitis (inflammation of the vertebrae) and discitis (inflammation of the vertebral disk space). After 48 hours, the biopsy sample grew Salmonella typhimurium and confirmed the diagnosis. The organism was sensitive to ceftriaxone and ciprofloxacin; parenteral ceftriaxone was continued and the patient wore a thoracolumbar brace for immobilization. For 3 days, her inflammatory marker levels were checked daily, then every other day for the rest of that first week, and then 2 more times in the following week.

DISCUSSION

Thoracic and lumbar vertebrae are the most common sites of spondylodiscitis.² Spondylodiscitis accounts for 3% to 5% of pyogenic osteomyelitis in patients in developed countries.³ The incidence of pyogenic spondylodiscitis may be rising due to an increase in the number of elderly and immunocompromised patients, as well as a rise in invasive medical procedures.^4-6

If left untreated, spondylodiscitis can spread longitudinally (involving the adjacent levels), posteriorly (causing bacterial meningitis, abscess formation, and cord compromise), or anteriorly (causing paravertebral abscess). Untreated spondylodiscitis can also send distant infective emboli and cause endocarditis^7-9 or mycotic abdominal aneurysm.¹⁰

Historically, mortality in patients with vertebral osteomyelitis has been as high as 25%.¹¹ The combination of earlier diagnosis, antibiotics, and surgical debridement and stabilization has decreased mortality to less than 15%.^12-14

Risk factors for spondylodiscitis include male sex, IV drug abuse, diabetes, morbid obesity, having had a genitourinary or spinal procedure, and being immunocompromised (eg, from alcohol abuse, malignancy, organ transplantation, chemotherapy, or corticosteroid use).^12,15,16

Gram-positive organisms cause most spine infections in both adults and children, with 40% to 90% caused by Staphylococcus aureus.¹⁷ Gram-negative organisms (Escherichia coli, Pseudomonas, and Proteus), which can also cause spondylodiscitis, typically occur after genitourinary infections or procedures. IV drug abusers are prone to Pseudomonas infections.¹⁸ Anaerobic infections may be seen in patients with diabetes or after penetrating trauma.¹⁵ Salmonella species can cause spondylodiscitis, especially in patients with sickle cell disease from an intestinal source.¹⁹

Mycobacterium tuberculosis is the most common nonpyogenic infecting agent that also can cause spondylodiscitis. Infection caused by tuberculosis (TB) has had a recent resurgence with resistant strains, especially in patients with human immunodeficiency virus.¹⁵ Although less than 10% of patients with TB have skeletal involvement, 50% of the skeletal involvement occurs in the spine.¹⁵

The clinical presentation of spondylodiscitis depends on the location of the infection, the virulence of the organism, and the immune status of the patient. Discitis can present as pain in the back, hip, abdomen (especially in children²⁰) and, occasionally, with meningeal involvement.¹¹ Patients with discitis often have a normal temperature.^15,21 In patients with discitis, the patient’s WCC will be normal, but the ESR is almost always elevated.^15,22 Suspect spondylodiscitis in patients who present with persistent or increasing pain 3 to 4 weeks after back surgery. For such patients, measure inflammatory markers and order imaging of the spine.

Risk factors for spondylodiscitis include IV drug abuse, diabetes, morbid obesity, and having had a genitourinary or spinal procedure. X-ray findings for patients with spondylodiscitis will include osteolysis and end plate erosions (early) and narrowing and collapse of the disk space (late). (In TB, relative preservation of the disk spaces is seen, with significant vertebral destruction.)

MRI is the modality of choice for diagnosis and assessment of suspected spondylodiscitis because it can provide imaging of the soft tissue, neural elements, and bony changes with a high sensitivity and specificity.²³ Once infection is suspected, the diagnosis should be confirmed by fluoroscopic- or computed tomography-guided biopsy before starting antibiotic treatment.

Long-term antibiotics
 are required to prevent recurrence


IV antibiotics are the mainstay of treatment for spondylodiscitis;²⁴ the specific drug used will depend upon the organism identified. Patients typically receive 2 to 6 weeks of IV therapy. Then, once the patient improves and inflammatory markers return to normal levels, the patient receives a course of oral antibiotics for 2 to 6 more weeks. Grados et al¹⁹ found recurrence rates of 10% to 15% for patients who were treated 4 to 8 weeks compared to 3.9% in those treated for 12 weeks or longer; therefore, a total duration of 12 weeks is commonly chosen.^25-28

To minimize the risk of spondylolisthesis, kyphosis, and fractures of the infected bone, patients are advised to rest and the spine is often immobilized with a spinal brace. Surgery may be needed if antibiotics are not effective, or for patients who develop complications such as fluid collection, neurologic deficits, or deformity.

Our patient’s pain improved after 2 weeks and she became more comfortable wearing the thoracolumbar brace. Her CRP and ESR also improved and there was no radiologic evidence of fluid collection. The patient was discharged with a peripherally inserted central catheter in place and received IV ceftriaxone for 6 more weeks at home. This was followed by 4 weeks of oral ciprofloxacin 750 mg twice daily, thereby completing a 12-week course of antibiotics.

Our patient’s response to treatment was monitored clinically and the inflammatory markers were checked weekly after discharge until the end of treatment and at 6 and 12 months after start of treatment. At 12 months, our patient’s CRP was <1 mg/dL and ESR was 22 mm/h. One year later, our patient remained asymptomatic with normal inflammatory marker levels and no evidence of recurrence.

THE TAKEAWAY

Spondylodiscitis is an important differential diagnosis of lower back, flank, groin, and buttock pain. It’s important to be aware of this diagnosis, especially in patients who have risk factors such as IV drug abuse, diabetes, and morbid obesity. Although previous spinal surgery is a risk factor, spondylodiscitis should be considered in patients with persistent back pain even if they haven’t had spinal surgery. It can be present even when there is no tenderness over the spinous process or any fever.

Checking inflammatory markers is a reasonable next step if a patient’s pain does not resolve after at least 4 weeks. If levels of inflammatory markers such as CRP and ESR are elevated and symptoms continue, MRI can confirm or rule out the presence of spondylodiscitis. Treatments include orthotic support, antibiotics, and surgical intervention when complications arise.

THE CASE

A 23-year-old immunocompetent woman was referred to our spinal clinic with a 6-month history of low back pain that radiated to her right flank, buttock, and groin. She’d had intermittent urinary problems, including mild dysuria and frequency, and had been treated with antibiotics for a presumed urinary tract infection on 3 previous occasions, but her pain gradually increased and eventually became constant.

The patient had no history of fever, malaise, or weight loss. She denied consuming unpasteurized milk or undercooked poultry, and hadn’t recently experienced diarrhea or vomiting.

Eight years earlier, she had undergone anterior fusion of her spine for idiopathic scoliosis. At that time, she was at Risser grade 1, and her Cobb angle was 50°; metallic instrumentation was implanted at T10 to L3 to prevent progression of the scoliosis. Her recovery had been uneventful.

During examination, her temperature, pulse, respiratory rate, blood pressure, and nervous system were all normal. Her hips appeared normal, as well, and a straight leg raise was negative bilaterally. The patient had mild midline lumbar tenderness. Spinal range of movement revealed decreased flexion and mild pain.

X-rays (FIGURE 1) showed no changes in the previous metalwork in her spine. There was decreased disk height at the L3/4 level, but no significant bony erosion or soft-tissue shadows. Laboratory testing revealed a C-reactive protein (CRP) level of 240 mg/dL (normal, <1 mg/dL) and her erythrocyte sedimentation rate (ESR) was 102 mm/h—more than 5 times higher than it should have been.¹ The patient had a normal peripheral white cell count (WCC). Midstream urine cultures were negative.


The patient was admitted to the hospital for further work-up. Magnetic resonance imaging (MRI) of the lumbar spine showed gross abnormality at the L3-L4 disk level with erosion of the end plates, fluid in the disk space, marked enhancing edema, and mild surrounding soft-tissue edematous changes, but no evidence of any epidural abscess (FIGURE 2). The patient had a fluoroscopy-guided needle biopsy of the disk on the same day and received intravenous (IV) ceftriaxone 2 g twice a day. Blood and urine cultures were negative.

THE DIAGNOSIS

We suspected our patient had spondylodiscitis, an infection of the spine that includes spondylitis (inflammation of the vertebrae) and discitis (inflammation of the vertebral disk space). After 48 hours, the biopsy sample grew Salmonella typhimurium and confirmed the diagnosis. The organism was sensitive to ceftriaxone and ciprofloxacin; parenteral ceftriaxone was continued and the patient wore a thoracolumbar brace for immobilization. For 3 days, her inflammatory marker levels were checked daily, then every other day for the rest of that first week, and then 2 more times in the following week.

DISCUSSION

Thoracic and lumbar vertebrae are the most common sites of spondylodiscitis.² Spondylodiscitis accounts for 3% to 5% of pyogenic osteomyelitis in patients in developed countries.³ The incidence of pyogenic spondylodiscitis may be rising due to an increase in the number of elderly and immunocompromised patients, as well as a rise in invasive medical procedures.^4-6

If left untreated, spondylodiscitis can spread longitudinally (involving the adjacent levels), posteriorly (causing bacterial meningitis, abscess formation, and cord compromise), or anteriorly (causing paravertebral abscess). Untreated spondylodiscitis can also send distant infective emboli and cause endocarditis^7-9 or mycotic abdominal aneurysm.¹⁰

Historically, mortality in patients with vertebral osteomyelitis has been as high as 25%.¹¹ The combination of earlier diagnosis, antibiotics, and surgical debridement and stabilization has decreased mortality to less than 15%.^12-14

Risk factors for spondylodiscitis include male sex, IV drug abuse, diabetes, morbid obesity, having had a genitourinary or spinal procedure, and being immunocompromised (eg, from alcohol abuse, malignancy, organ transplantation, chemotherapy, or corticosteroid use).^12,15,16

Gram-positive organisms cause most spine infections in both adults and children, with 40% to 90% caused by Staphylococcus aureus.¹⁷ Gram-negative organisms (Escherichia coli, Pseudomonas, and Proteus), which can also cause spondylodiscitis, typically occur after genitourinary infections or procedures. IV drug abusers are prone to Pseudomonas infections.¹⁸ Anaerobic infections may be seen in patients with diabetes or after penetrating trauma.¹⁵ Salmonella species can cause spondylodiscitis, especially in patients with sickle cell disease from an intestinal source.¹⁹

Mycobacterium tuberculosis is the most common nonpyogenic infecting agent that also can cause spondylodiscitis. Infection caused by tuberculosis (TB) has had a recent resurgence with resistant strains, especially in patients with human immunodeficiency virus.¹⁵ Although less than 10% of patients with TB have skeletal involvement, 50% of the skeletal involvement occurs in the spine.¹⁵

The clinical presentation of spondylodiscitis depends on the location of the infection, the virulence of the organism, and the immune status of the patient. Discitis can present as pain in the back, hip, abdomen (especially in children²⁰) and, occasionally, with meningeal involvement.¹¹ Patients with discitis often have a normal temperature.^15,21 In patients with discitis, the patient’s WCC will be normal, but the ESR is almost always elevated.^15,22 Suspect spondylodiscitis in patients who present with persistent or increasing pain 3 to 4 weeks after back surgery. For such patients, measure inflammatory markers and order imaging of the spine.

Risk factors for spondylodiscitis include IV drug abuse, diabetes, morbid obesity, and having had a genitourinary or spinal procedure. X-ray findings for patients with spondylodiscitis will include osteolysis and end plate erosions (early) and narrowing and collapse of the disk space (late). (In TB, relative preservation of the disk spaces is seen, with significant vertebral destruction.)

MRI is the modality of choice for diagnosis and assessment of suspected spondylodiscitis because it can provide imaging of the soft tissue, neural elements, and bony changes with a high sensitivity and specificity.²³ Once infection is suspected, the diagnosis should be confirmed by fluoroscopic- or computed tomography-guided biopsy before starting antibiotic treatment.

Long-term antibiotics
 are required to prevent recurrence


IV antibiotics are the mainstay of treatment for spondylodiscitis;²⁴ the specific drug used will depend upon the organism identified. Patients typically receive 2 to 6 weeks of IV therapy. Then, once the patient improves and inflammatory markers return to normal levels, the patient receives a course of oral antibiotics for 2 to 6 more weeks. Grados et al¹⁹ found recurrence rates of 10% to 15% for patients who were treated 4 to 8 weeks compared to 3.9% in those treated for 12 weeks or longer; therefore, a total duration of 12 weeks is commonly chosen.^25-28

To minimize the risk of spondylolisthesis, kyphosis, and fractures of the infected bone, patients are advised to rest and the spine is often immobilized with a spinal brace. Surgery may be needed if antibiotics are not effective, or for patients who develop complications such as fluid collection, neurologic deficits, or deformity.

Our patient’s pain improved after 2 weeks and she became more comfortable wearing the thoracolumbar brace. Her CRP and ESR also improved and there was no radiologic evidence of fluid collection. The patient was discharged with a peripherally inserted central catheter in place and received IV ceftriaxone for 6 more weeks at home. This was followed by 4 weeks of oral ciprofloxacin 750 mg twice daily, thereby completing a 12-week course of antibiotics.

Our patient’s response to treatment was monitored clinically and the inflammatory markers were checked weekly after discharge until the end of treatment and at 6 and 12 months after start of treatment. At 12 months, our patient’s CRP was <1 mg/dL and ESR was 22 mm/h. One year later, our patient remained asymptomatic with normal inflammatory marker levels and no evidence of recurrence.

THE TAKEAWAY

Spondylodiscitis is an important differential diagnosis of lower back, flank, groin, and buttock pain. It’s important to be aware of this diagnosis, especially in patients who have risk factors such as IV drug abuse, diabetes, and morbid obesity. Although previous spinal surgery is a risk factor, spondylodiscitis should be considered in patients with persistent back pain even if they haven’t had spinal surgery. It can be present even when there is no tenderness over the spinous process or any fever.

Checking inflammatory markers is a reasonable next step if a patient’s pain does not resolve after at least 4 weeks. If levels of inflammatory markers such as CRP and ESR are elevated and symptoms continue, MRI can confirm or rule out the presence of spondylodiscitis. Treatments include orthotic support, antibiotics, and surgical intervention when complications arise.

THE CASE

A 23-year-old immunocompetent woman was referred to our spinal clinic with a 6-month history of low back pain that radiated to her right flank, buttock, and groin. She’d had intermittent urinary problems, including mild dysuria and frequency, and had been treated with antibiotics for a presumed urinary tract infection on 3 previous occasions, but her pain gradually increased and eventually became constant.

The patient had no history of fever, malaise, or weight loss. She denied consuming unpasteurized milk or undercooked poultry, and hadn’t recently experienced diarrhea or vomiting.

Eight years earlier, she had undergone anterior fusion of her spine for idiopathic scoliosis. At that time, she was at Risser grade 1, and her Cobb angle was 50°; metallic instrumentation was implanted at T10 to L3 to prevent progression of the scoliosis. Her recovery had been uneventful.

During examination, her temperature, pulse, respiratory rate, blood pressure, and nervous system were all normal. Her hips appeared normal, as well, and a straight leg raise was negative bilaterally. The patient had mild midline lumbar tenderness. Spinal range of movement revealed decreased flexion and mild pain.

X-rays (FIGURE 1) showed no changes in the previous metalwork in her spine. There was decreased disk height at the L3/4 level, but no significant bony erosion or soft-tissue shadows. Laboratory testing revealed a C-reactive protein (CRP) level of 240 mg/dL (normal, <1 mg/dL) and her erythrocyte sedimentation rate (ESR) was 102 mm/h—more than 5 times higher than it should have been.¹ The patient had a normal peripheral white cell count (WCC). Midstream urine cultures were negative.


The patient was admitted to the hospital for further work-up. Magnetic resonance imaging (MRI) of the lumbar spine showed gross abnormality at the L3-L4 disk level with erosion of the end plates, fluid in the disk space, marked enhancing edema, and mild surrounding soft-tissue edematous changes, but no evidence of any epidural abscess (FIGURE 2). The patient had a fluoroscopy-guided needle biopsy of the disk on the same day and received intravenous (IV) ceftriaxone 2 g twice a day. Blood and urine cultures were negative.

THE DIAGNOSIS

We suspected our patient had spondylodiscitis, an infection of the spine that includes spondylitis (inflammation of the vertebrae) and discitis (inflammation of the vertebral disk space). After 48 hours, the biopsy sample grew Salmonella typhimurium and confirmed the diagnosis. The organism was sensitive to ceftriaxone and ciprofloxacin; parenteral ceftriaxone was continued and the patient wore a thoracolumbar brace for immobilization. For 3 days, her inflammatory marker levels were checked daily, then every other day for the rest of that first week, and then 2 more times in the following week.

DISCUSSION

Thoracic and lumbar vertebrae are the most common sites of spondylodiscitis.² Spondylodiscitis accounts for 3% to 5% of pyogenic osteomyelitis in patients in developed countries.³ The incidence of pyogenic spondylodiscitis may be rising due to an increase in the number of elderly and immunocompromised patients, as well as a rise in invasive medical procedures.^4-6

If left untreated, spondylodiscitis can spread longitudinally (involving the adjacent levels), posteriorly (causing bacterial meningitis, abscess formation, and cord compromise), or anteriorly (causing paravertebral abscess). Untreated spondylodiscitis can also send distant infective emboli and cause endocarditis^7-9 or mycotic abdominal aneurysm.¹⁰

Historically, mortality in patients with vertebral osteomyelitis has been as high as 25%.¹¹ The combination of earlier diagnosis, antibiotics, and surgical debridement and stabilization has decreased mortality to less than 15%.^12-14

Risk factors for spondylodiscitis include male sex, IV drug abuse, diabetes, morbid obesity, having had a genitourinary or spinal procedure, and being immunocompromised (eg, from alcohol abuse, malignancy, organ transplantation, chemotherapy, or corticosteroid use).^12,15,16

Gram-positive organisms cause most spine infections in both adults and children, with 40% to 90% caused by Staphylococcus aureus.¹⁷ Gram-negative organisms (Escherichia coli, Pseudomonas, and Proteus), which can also cause spondylodiscitis, typically occur after genitourinary infections or procedures. IV drug abusers are prone to Pseudomonas infections.¹⁸ Anaerobic infections may be seen in patients with diabetes or after penetrating trauma.¹⁵ Salmonella species can cause spondylodiscitis, especially in patients with sickle cell disease from an intestinal source.¹⁹

Mycobacterium tuberculosis is the most common nonpyogenic infecting agent that also can cause spondylodiscitis. Infection caused by tuberculosis (TB) has had a recent resurgence with resistant strains, especially in patients with human immunodeficiency virus.¹⁵ Although less than 10% of patients with TB have skeletal involvement, 50% of the skeletal involvement occurs in the spine.¹⁵

The clinical presentation of spondylodiscitis depends on the location of the infection, the virulence of the organism, and the immune status of the patient. Discitis can present as pain in the back, hip, abdomen (especially in children²⁰) and, occasionally, with meningeal involvement.¹¹ Patients with discitis often have a normal temperature.^15,21 In patients with discitis, the patient’s WCC will be normal, but the ESR is almost always elevated.^15,22 Suspect spondylodiscitis in patients who present with persistent or increasing pain 3 to 4 weeks after back surgery. For such patients, measure inflammatory markers and order imaging of the spine.

Risk factors for spondylodiscitis include IV drug abuse, diabetes, morbid obesity, and having had a genitourinary or spinal procedure. X-ray findings for patients with spondylodiscitis will include osteolysis and end plate erosions (early) and narrowing and collapse of the disk space (late). (In TB, relative preservation of the disk spaces is seen, with significant vertebral destruction.)

MRI is the modality of choice for diagnosis and assessment of suspected spondylodiscitis because it can provide imaging of the soft tissue, neural elements, and bony changes with a high sensitivity and specificity.²³ Once infection is suspected, the diagnosis should be confirmed by fluoroscopic- or computed tomography-guided biopsy before starting antibiotic treatment.

Long-term antibiotics
 are required to prevent recurrence


IV antibiotics are the mainstay of treatment for spondylodiscitis;²⁴ the specific drug used will depend upon the organism identified. Patients typically receive 2 to 6 weeks of IV therapy. Then, once the patient improves and inflammatory markers return to normal levels, the patient receives a course of oral antibiotics for 2 to 6 more weeks. Grados et al¹⁹ found recurrence rates of 10% to 15% for patients who were treated 4 to 8 weeks compared to 3.9% in those treated for 12 weeks or longer; therefore, a total duration of 12 weeks is commonly chosen.^25-28

To minimize the risk of spondylolisthesis, kyphosis, and fractures of the infected bone, patients are advised to rest and the spine is often immobilized with a spinal brace. Surgery may be needed if antibiotics are not effective, or for patients who develop complications such as fluid collection, neurologic deficits, or deformity.

Our patient’s pain improved after 2 weeks and she became more comfortable wearing the thoracolumbar brace. Her CRP and ESR also improved and there was no radiologic evidence of fluid collection. The patient was discharged with a peripherally inserted central catheter in place and received IV ceftriaxone for 6 more weeks at home. This was followed by 4 weeks of oral ciprofloxacin 750 mg twice daily, thereby completing a 12-week course of antibiotics.

Our patient’s response to treatment was monitored clinically and the inflammatory markers were checked weekly after discharge until the end of treatment and at 6 and 12 months after start of treatment. At 12 months, our patient’s CRP was <1 mg/dL and ESR was 22 mm/h. One year later, our patient remained asymptomatic with normal inflammatory marker levels and no evidence of recurrence.

THE TAKEAWAY

Spondylodiscitis is an important differential diagnosis of lower back, flank, groin, and buttock pain. It’s important to be aware of this diagnosis, especially in patients who have risk factors such as IV drug abuse, diabetes, and morbid obesity. Although previous spinal surgery is a risk factor, spondylodiscitis should be considered in patients with persistent back pain even if they haven’t had spinal surgery. It can be present even when there is no tenderness over the spinous process or any fever.

Checking inflammatory markers is a reasonable next step if a patient’s pain does not resolve after at least 4 weeks. If levels of inflammatory markers such as CRP and ESR are elevated and symptoms continue, MRI can confirm or rule out the presence of spondylodiscitis. Treatments include orthotic support, antibiotics, and surgical intervention when complications arise.

CASE › Marie C, a 75-year-old Asian woman, reports weakness in her legs and arms with unsteadiness when walking. She has a vague but persistent ache in her large muscles. Her symptoms have developed slowly over the past 3 months. She denies recent signs or symptoms of infection or other illness. Her medical history includes hypertension, hyperlipidemia, osteopenia, and obesity. Ms. C takes lisinopril 10 mg/d and atorvastatin, which was recently increased from 10 to 20 mg/d.

What would your next steps be in caring for this patient?

Patients who experience muscle-related symptoms such as pain, fatigue, or weakness often seek help from their family physician (FP). The list of possible causes of these complaints can be lengthy and vary greatly, from nonmyopathic conditions such as fibromyalgia to worrisome forms of myopathy such as inclusion body myositis or polymyositis. This article will help you to quickly identify which patients with muscle-related complaints should be evaluated for myopathy and what your work-up should include.

Myopathy or not?

Distinguishing between myopathy and nonmyopathic muscle pain or weakness is the first step in evaluating patients with muscle-related complaints. Many conditions share muscle-related symptoms, but actual muscle damage is not always present (eg, fibromyalgia, chronic pain, and chronic fatigue syndromes).¹ While there is some overlap in presentation between patients with myopathy and nonmyopathic conditions, there are important differences in symptoms, physical exam findings, and lab test results (TABLE 1^1-4). Notably, in myopathic disease, patients’ symptoms are usually progressive, vital signs are abnormal, and weakness is common, whereas patients with nonmyopathic disease typically have remitting and relapsing symptoms, normal vital signs, and no weakness.

Myopathy itself is divided into 3 categories—myositic, intrinsic, and toxic—which reflect the condition, or medication, that brought on the muscle damage (TABLE 2^2,4-15). Placing patients into one of these categories based on their risk factors, history, and physical exam findings can help to focus the diagnostic work-up on areas most likely to provide useful information.

Myositic myopathy can be caused by infection or autoimmunity

Myositic myopathies result in inflammatory destruction of muscle tissue. Patients with myositic myopathy often exhibit fever, malaise, weight loss, and general fatigue. Though weakness and pain are common, both can be variable or even absent in myositic myopathy.^2,5 Myositic myopathy can be caused by infectious agents or can develop from an autoimmune disease.

Infectious myositic myopathy is one of the more common types of myopathy that FPs will encounter.² Viruses such as influenza, parainfluenza, coxsackievirus, human immunodeficiency virus, cytomegalovirus, echovirus, adenovirus, Epstein-Barr, and hepatitis C are common causes.^2,4,16 Patients with 
a viral myositis often report prodromal symptoms such as fever, upper respiratory illness, or GI distress one to 2 weeks before the onset of muscle complaints. Bacterial and fungal myositides are relatively rare. Both most often occur as the result of penetrating trauma or immunocompromise, and are generally not subtle.² Parasitic myopathy can occur from the invasion of skeletal muscle by trichinella after ingesting undercooked, infected meat.² Although previously a more common problem, currently only 10 to 20 cases of trichinellosis are reported in the United States each year.¹⁷ Due to their rarity, bacterial, fungal, and parasitic myositides are not reviewed here.

Patients with a viral myositis often report prodromal symptoms such as fever, upper respiratory illness, or gastrointestinal distress one to 2 weeks before the onset of muscle complaints. Muscle pain is usually multifocal, involving larger, bilateral muscle groups, and may be associated with swelling.

Patients with viral myositis may exhibit diffusely painful, swollen, or boggy-feeling muscles as well as weakness and pain with exertion. Other signs of viral infection such as rash, fever, upper respiratory symptoms, or meningeal signs may be present. Severe signs include arrhythmia or respiratory failure due to cardiac muscle or diaphragm involvement, or signs of renal failure due to precipitation of myoglobin in the renal system (ie, rhabdomyolysis).² If the infection affects the heart, patients may develop palpitations, pleuritic chest pain, or shortness of breath.²

Diagnosis of viral myositis relies heavily on clinical suspicion in patients with a fitting history and physical exam findings. Helpful lab tests include a complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), creatine kinase (CK), and liver function tests (LFTs), all of which can be abnormal in viral myositis. Viral polymerase chain reaction, culture, or antigen testing may be helpful in severe or confusing cases, but in most cases such testing is unnecessary. Muscle biopsy is not recommended except in persistent cases, where definitive identification of the causative agent might alter treatment or when nonviral infection is suspected.²

Autoimmune myositic myopathy. Unlike infectious myopathies, autoimmune myopathies are usually chronic, subtle, and relatively rare. The 3 most common autoimmune myopathies—polymyositis, dermatomyositis, and inclusion body myositis—have a combined prevalence of approximately 10:100,000.⁶ Although these types of myopathies are uncommon, FPs will likely be the first to evaluate a patient with one of them.

Patients with an autoimmune myopathy typically complain of weakness and mild to moderate muscle pain, although pain may be absent. Compared to infectious myopathies, autoimmune myopathies usually exhibit a more indolent course. Patients with advanced disease may report fever, weight loss, shortness of breath from cardiomyopathy, heartburn from a weakened lower esophageal sphincter, and/or a rash.⁵

A patient
 with mild
 to moderate electrolyte problems may complain of muscle fatigue, weakness,
 or pain. Physical examination may reveal symmetric, proximal muscle weakness. Atrophy is typically not seen until late in the disease. Skin exam usually is normal in patients with inclusion body myositis and polymyositis. The typical rash of dermatomyositis is a heliotrope (blue-purple) discoloration on the upper eyelids and a raised, violaceous, scaly eruption on the knuckles (Gottron’s papules).

Laboratory tests that can be helpful include CK, lactate dehydrogenase (LDH), aldolase, and LFTs (reflecting muscle injury, not liver involvement). For polymyositis and dermatomyositis, CK is the most sensitive lab test and often exhibits the highest elevation above normal.⁶ Conversely, CK is often normal or only mildly elevated in inclusion body myositis. Up to 80% of patients with autoimmune myopathy will have antinuclear antibodies.^3,5 ESR and CRP levels are also often elevated.

Both electromyography (EMG) and muscle biopsy may be required to diagnose autoimmune myopathy, but these are typically done under the direction of a rheumatologist after an FP’s initial work-up is inconclusive.

Intrinsic myopathy: Suspect electrolyte problems, other causes

Intrinsic myopathy occurs in patients with electrolyte disorders, diseases of the endocrine system, or underlying metabolic dysfunction.

Electrolyte disorders. Muscle-related symptoms are unlikely to be the chief complaint of patients with severe electrolyte imbalance. However, a patient with mild to moderate electrolyte problems may develop muscle fatigue, weakness, or pain. TABLE 3 reviews other signs and symptoms of electrolyte abnormalities that may be helpful in establishing a diagnosis in a patient with muscle complaints.

Ordering a complete metabolic panel (CMP), CK, and urinalysis (UA) can help rule out electrolyte disorders. If electrolyte disorders are detected, an electrocardiogram is useful to evaluate for cardiac dysfunction. Once an electrolyte disorder is identified, investigate its underlying cause. Correcting the electrolyte disorder should help improve symptoms of myopathy.

Endocrine myopathy can be associated with hypothyroidism, hyperthyroidism, parathyroid disease, vitamin D deficiency, or Cushing syndrome.^8-10,18,19 Although less common than some other causes, identifying endocrine myopathy is crucial because correcting the underlying disease will often improve multiple aspects of the patient’s health.

The presentation of endocrine myopathy may be subtle. Patients with hypothyroidism may experience muscle pain or weakness, fatigue, cold sensitivity, constipation, and dry skin.²⁰ Muscle-related symptoms may be the only sign of endocrine myopathy in a patient who would otherwise be considered to have subclinical hypothyroidism.^8,18 Hyperthyroidism can present with weight loss, heat intolerance, frequent bowel movements, tachycardia, and muscle weakness.²¹

Patients with parathyroid disease— especially patients with chronic renal failure—may report proximal muscle weakness, often in the lower extremities.¹⁹ Complaints of muscle weakness or pain can occur with severe vitamin D deficiency.¹⁰ Patients with Cushing syndrome often experience proximal weakness and weight gain.⁹

Patients with a personal or family history of endocrine disorders, previous thyroid surgery, or those taking medications that can impair thyroid function, such as lithium, amiodarone, or interferon, are at risk for endocrine myopathy.^18-20 Suspect hyperparathyroidism in patients with chronic kidney disease who complain of weakness.

Vitamin D deficiency is relatively common, with at minimum 20% of elderly adults estimated to be deficient.¹⁰ Patients at risk for Cushing disease are most likely receiving pharmacologic doses of glucocorticoids, which can increase their risk of myopathy, or to have ectopic adrenocorticotropic hormone secretion.

Metabolic myopathy results from a lack of sufficient energy production in the muscle. The 3 main groups of metabolic myopathy are impaired muscle glycogenoses, disorders of fatty acid oxidation, and mitochondrial myopathies.⁷

Because metabolic myopathy can occur at any age, a thorough history and physical is crucial for diagnosis. Proximal weakness in metabolic myopathy is often associated with exercise intolerance, stressful illness, or fasting. Patients often present with dynamic abnormalities such as fatigue, muscle cramping, and even rhabdomyolysis during exertion.⁷

When evaluating patients you suspect may have metabolic myopathy, a physical exam may reveal muscle contractures, muscle swelling, or proximal muscle weakness. Patients with certain types of fatty acid oxidation disorders or mitochondrial disorders may also exhibit cardiomyopathy, neuropathy, retinopathy, ataxia, hearing loss, or other systemic manifestations.⁷

Basic labs for investigating suspected metabolic myopathy include serum electrolytes, glucose, LFTs, CK (which may or may not be elevated), lactate, ammonia, and UA for myoglobinuria. More advanced labs, such as serum total carnitine and acylcarnitine as well as urinary levels of dicarboxylic acids and acylglycines, may be needed if a metabolic disorder is strongly suspected.⁷ Muscle biopsy, EMG, and genetic testing can also prove helpful in diagnosis. Definitive diagnosis and treatment of metabolic myopathy usually requires a multidisciplinary team of providers, including subspecialty referral.

Toxic myopathy

The symptoms of drug-induced toxic myopathy are usually more insidious and lab abnormalities are usually more subtle than for other forms
 of myopathy. Toxic myopathy refers to muscle damage caused by an exogenous chemical agent, most often a drug. The mechanism of toxicity is not always clear and may result from the activation of inflammatory responses similar to autoimmune myopathy.²² Toxic myopathies may result from several commonly used medications; cholesterol-lowering medications are a common culprit.^13-15,23-25 Drug-induced myopathies vary in frequency and severity. For instance, in patients taking statins, the rate of myalgias is 6%, while the incidence of rhabdomyolysis is estimated to be 4 per 100,000, and is found most often in patients taking concomitant fibrates.²³

Drug-induced toxic myopathy differs from previously discussed myopathies in that symptoms are usually more insidious, findings on exam are more often mixed muscular and neurologic, and lab abnormalities are usually more subtle.^11,12 Symptoms of myopathy typically occur weeks or months after initiating a drug and usually improve or resolve within weeks after discontinuing the offending agent. Knowing the patient’s medication list and which medications cause certain patterns of myopathy symptoms can help guide the differential diagnosis (TABLE 4^11-15,22-25).

Cholesterol-lowering medications such as statins are a common cause of toxic myopathy. Risk factors for most medication-related myopathies are polypharmacy, renal or liver disease, and age over 50 years^13-15,23-25 The physical exam for patients with drug- or toxin-related myopathy will most often reveal relatively minor abnormalities such as muscle tenderness and mild weakness, except for the most severe or advanced cases. Most patients will not have physical signs that suggest an underlying illness. CK levels and LFTs should be obtained. Basic chemistry and UA may also be helpful in patients with risk factors for renal disease.

CASE › Ms. C has been taking a statin for more than 10 years, and the dose was recently increased. You are aware that statin-related muscle injury can develop even after years of use, and suspect the statin may be causing her myopathy. You order a CK test, which is mildly elevated. You recommend discontinuing the statin. After 8 weeks off her statin, Ms. C’s Symptoms do not improve. Given her lack of systemic complaints, myositic myopathy from an infectious or rheumatologic cause seems unlikely. You begin to consider an intrinsic cause of myopathy, and order the following tests: a CMP, UA, thyroid-stimulating hormone, repeat CK, and vitamin D level. This testing reveals a vitamin D deficiency at 17 ng/ml (normal range: 30-74 ng/ml). You recommend vitamin D, 50,000 IU per week for 8 weeks. At follow-up, Ms. C's vitamin D level is 40. She says she feels better and her muscle complaints have resolved.

CORRESPONDENCE
Brent W. Smith, MD, Travis Air Force Base Family Medicine Residency, 101 Bodin Circle, Travis Air Force Base, CA 94535; smithb@smithnet.us

CASE › Marie C, a 75-year-old Asian woman, reports weakness in her legs and arms with unsteadiness when walking. She has a vague but persistent ache in her large muscles. Her symptoms have developed slowly over the past 3 months. She denies recent signs or symptoms of infection or other illness. Her medical history includes hypertension, hyperlipidemia, osteopenia, and obesity. Ms. C takes lisinopril 10 mg/d and atorvastatin, which was recently increased from 10 to 20 mg/d.

What would your next steps be in caring for this patient?

Patients who experience muscle-related symptoms such as pain, fatigue, or weakness often seek help from their family physician (FP). The list of possible causes of these complaints can be lengthy and vary greatly, from nonmyopathic conditions such as fibromyalgia to worrisome forms of myopathy such as inclusion body myositis or polymyositis. This article will help you to quickly identify which patients with muscle-related complaints should be evaluated for myopathy and what your work-up should include.

Myopathy or not?

Distinguishing between myopathy and nonmyopathic muscle pain or weakness is the first step in evaluating patients with muscle-related complaints. Many conditions share muscle-related symptoms, but actual muscle damage is not always present (eg, fibromyalgia, chronic pain, and chronic fatigue syndromes).¹ While there is some overlap in presentation between patients with myopathy and nonmyopathic conditions, there are important differences in symptoms, physical exam findings, and lab test results (TABLE 1^1-4). Notably, in myopathic disease, patients’ symptoms are usually progressive, vital signs are abnormal, and weakness is common, whereas patients with nonmyopathic disease typically have remitting and relapsing symptoms, normal vital signs, and no weakness.

Myopathy itself is divided into 3 categories—myositic, intrinsic, and toxic—which reflect the condition, or medication, that brought on the muscle damage (TABLE 2^2,4-15). Placing patients into one of these categories based on their risk factors, history, and physical exam findings can help to focus the diagnostic work-up on areas most likely to provide useful information.

Myositic myopathy can be caused by infection or autoimmunity

Myositic myopathies result in inflammatory destruction of muscle tissue. Patients with myositic myopathy often exhibit fever, malaise, weight loss, and general fatigue. Though weakness and pain are common, both can be variable or even absent in myositic myopathy.^2,5 Myositic myopathy can be caused by infectious agents or can develop from an autoimmune disease.

Infectious myositic myopathy is one of the more common types of myopathy that FPs will encounter.² Viruses such as influenza, parainfluenza, coxsackievirus, human immunodeficiency virus, cytomegalovirus, echovirus, adenovirus, Epstein-Barr, and hepatitis C are common causes.^2,4,16 Patients with 
a viral myositis often report prodromal symptoms such as fever, upper respiratory illness, or GI distress one to 2 weeks before the onset of muscle complaints. Bacterial and fungal myositides are relatively rare. Both most often occur as the result of penetrating trauma or immunocompromise, and are generally not subtle.² Parasitic myopathy can occur from the invasion of skeletal muscle by trichinella after ingesting undercooked, infected meat.² Although previously a more common problem, currently only 10 to 20 cases of trichinellosis are reported in the United States each year.¹⁷ Due to their rarity, bacterial, fungal, and parasitic myositides are not reviewed here.

Patients with a viral myositis often report prodromal symptoms such as fever, upper respiratory illness, or gastrointestinal distress one to 2 weeks before the onset of muscle complaints. Muscle pain is usually multifocal, involving larger, bilateral muscle groups, and may be associated with swelling.

Patients with viral myositis may exhibit diffusely painful, swollen, or boggy-feeling muscles as well as weakness and pain with exertion. Other signs of viral infection such as rash, fever, upper respiratory symptoms, or meningeal signs may be present. Severe signs include arrhythmia or respiratory failure due to cardiac muscle or diaphragm involvement, or signs of renal failure due to precipitation of myoglobin in the renal system (ie, rhabdomyolysis).² If the infection affects the heart, patients may develop palpitations, pleuritic chest pain, or shortness of breath.²

Diagnosis of viral myositis relies heavily on clinical suspicion in patients with a fitting history and physical exam findings. Helpful lab tests include a complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), creatine kinase (CK), and liver function tests (LFTs), all of which can be abnormal in viral myositis. Viral polymerase chain reaction, culture, or antigen testing may be helpful in severe or confusing cases, but in most cases such testing is unnecessary. Muscle biopsy is not recommended except in persistent cases, where definitive identification of the causative agent might alter treatment or when nonviral infection is suspected.²

Autoimmune myositic myopathy. Unlike infectious myopathies, autoimmune myopathies are usually chronic, subtle, and relatively rare. The 3 most common autoimmune myopathies—polymyositis, dermatomyositis, and inclusion body myositis—have a combined prevalence of approximately 10:100,000.⁶ Although these types of myopathies are uncommon, FPs will likely be the first to evaluate a patient with one of them.

Patients with an autoimmune myopathy typically complain of weakness and mild to moderate muscle pain, although pain may be absent. Compared to infectious myopathies, autoimmune myopathies usually exhibit a more indolent course. Patients with advanced disease may report fever, weight loss, shortness of breath from cardiomyopathy, heartburn from a weakened lower esophageal sphincter, and/or a rash.⁵

A patient
 with mild
 to moderate electrolyte problems may complain of muscle fatigue, weakness,
 or pain. Physical examination may reveal symmetric, proximal muscle weakness. Atrophy is typically not seen until late in the disease. Skin exam usually is normal in patients with inclusion body myositis and polymyositis. The typical rash of dermatomyositis is a heliotrope (blue-purple) discoloration on the upper eyelids and a raised, violaceous, scaly eruption on the knuckles (Gottron’s papules).

Laboratory tests that can be helpful include CK, lactate dehydrogenase (LDH), aldolase, and LFTs (reflecting muscle injury, not liver involvement). For polymyositis and dermatomyositis, CK is the most sensitive lab test and often exhibits the highest elevation above normal.⁶ Conversely, CK is often normal or only mildly elevated in inclusion body myositis. Up to 80% of patients with autoimmune myopathy will have antinuclear antibodies.^3,5 ESR and CRP levels are also often elevated.

Both electromyography (EMG) and muscle biopsy may be required to diagnose autoimmune myopathy, but these are typically done under the direction of a rheumatologist after an FP’s initial work-up is inconclusive.

Intrinsic myopathy: Suspect electrolyte problems, other causes

Intrinsic myopathy occurs in patients with electrolyte disorders, diseases of the endocrine system, or underlying metabolic dysfunction.

Electrolyte disorders. Muscle-related symptoms are unlikely to be the chief complaint of patients with severe electrolyte imbalance. However, a patient with mild to moderate electrolyte problems may develop muscle fatigue, weakness, or pain. TABLE 3 reviews other signs and symptoms of electrolyte abnormalities that may be helpful in establishing a diagnosis in a patient with muscle complaints.

Ordering a complete metabolic panel (CMP), CK, and urinalysis (UA) can help rule out electrolyte disorders. If electrolyte disorders are detected, an electrocardiogram is useful to evaluate for cardiac dysfunction. Once an electrolyte disorder is identified, investigate its underlying cause. Correcting the electrolyte disorder should help improve symptoms of myopathy.

Endocrine myopathy can be associated with hypothyroidism, hyperthyroidism, parathyroid disease, vitamin D deficiency, or Cushing syndrome.^8-10,18,19 Although less common than some other causes, identifying endocrine myopathy is crucial because correcting the underlying disease will often improve multiple aspects of the patient’s health.

The presentation of endocrine myopathy may be subtle. Patients with hypothyroidism may experience muscle pain or weakness, fatigue, cold sensitivity, constipation, and dry skin.²⁰ Muscle-related symptoms may be the only sign of endocrine myopathy in a patient who would otherwise be considered to have subclinical hypothyroidism.^8,18 Hyperthyroidism can present with weight loss, heat intolerance, frequent bowel movements, tachycardia, and muscle weakness.²¹

Patients with parathyroid disease— especially patients with chronic renal failure—may report proximal muscle weakness, often in the lower extremities.¹⁹ Complaints of muscle weakness or pain can occur with severe vitamin D deficiency.¹⁰ Patients with Cushing syndrome often experience proximal weakness and weight gain.⁹

Patients with a personal or family history of endocrine disorders, previous thyroid surgery, or those taking medications that can impair thyroid function, such as lithium, amiodarone, or interferon, are at risk for endocrine myopathy.^18-20 Suspect hyperparathyroidism in patients with chronic kidney disease who complain of weakness.

Vitamin D deficiency is relatively common, with at minimum 20% of elderly adults estimated to be deficient.¹⁰ Patients at risk for Cushing disease are most likely receiving pharmacologic doses of glucocorticoids, which can increase their risk of myopathy, or to have ectopic adrenocorticotropic hormone secretion.

Metabolic myopathy results from a lack of sufficient energy production in the muscle. The 3 main groups of metabolic myopathy are impaired muscle glycogenoses, disorders of fatty acid oxidation, and mitochondrial myopathies.⁷

Because metabolic myopathy can occur at any age, a thorough history and physical is crucial for diagnosis. Proximal weakness in metabolic myopathy is often associated with exercise intolerance, stressful illness, or fasting. Patients often present with dynamic abnormalities such as fatigue, muscle cramping, and even rhabdomyolysis during exertion.⁷

When evaluating patients you suspect may have metabolic myopathy, a physical exam may reveal muscle contractures, muscle swelling, or proximal muscle weakness. Patients with certain types of fatty acid oxidation disorders or mitochondrial disorders may also exhibit cardiomyopathy, neuropathy, retinopathy, ataxia, hearing loss, or other systemic manifestations.⁷

Basic labs for investigating suspected metabolic myopathy include serum electrolytes, glucose, LFTs, CK (which may or may not be elevated), lactate, ammonia, and UA for myoglobinuria. More advanced labs, such as serum total carnitine and acylcarnitine as well as urinary levels of dicarboxylic acids and acylglycines, may be needed if a metabolic disorder is strongly suspected.⁷ Muscle biopsy, EMG, and genetic testing can also prove helpful in diagnosis. Definitive diagnosis and treatment of metabolic myopathy usually requires a multidisciplinary team of providers, including subspecialty referral.

Toxic myopathy

The symptoms of drug-induced toxic myopathy are usually more insidious and lab abnormalities are usually more subtle than for other forms
 of myopathy. Toxic myopathy refers to muscle damage caused by an exogenous chemical agent, most often a drug. The mechanism of toxicity is not always clear and may result from the activation of inflammatory responses similar to autoimmune myopathy.²² Toxic myopathies may result from several commonly used medications; cholesterol-lowering medications are a common culprit.^13-15,23-25 Drug-induced myopathies vary in frequency and severity. For instance, in patients taking statins, the rate of myalgias is 6%, while the incidence of rhabdomyolysis is estimated to be 4 per 100,000, and is found most often in patients taking concomitant fibrates.²³

Drug-induced toxic myopathy differs from previously discussed myopathies in that symptoms are usually more insidious, findings on exam are more often mixed muscular and neurologic, and lab abnormalities are usually more subtle.^11,12 Symptoms of myopathy typically occur weeks or months after initiating a drug and usually improve or resolve within weeks after discontinuing the offending agent. Knowing the patient’s medication list and which medications cause certain patterns of myopathy symptoms can help guide the differential diagnosis (TABLE 4^11-15,22-25).

Cholesterol-lowering medications such as statins are a common cause of toxic myopathy. Risk factors for most medication-related myopathies are polypharmacy, renal or liver disease, and age over 50 years^13-15,23-25 The physical exam for patients with drug- or toxin-related myopathy will most often reveal relatively minor abnormalities such as muscle tenderness and mild weakness, except for the most severe or advanced cases. Most patients will not have physical signs that suggest an underlying illness. CK levels and LFTs should be obtained. Basic chemistry and UA may also be helpful in patients with risk factors for renal disease.

CASE › Ms. C has been taking a statin for more than 10 years, and the dose was recently increased. You are aware that statin-related muscle injury can develop even after years of use, and suspect the statin may be causing her myopathy. You order a CK test, which is mildly elevated. You recommend discontinuing the statin. After 8 weeks off her statin, Ms. C’s Symptoms do not improve. Given her lack of systemic complaints, myositic myopathy from an infectious or rheumatologic cause seems unlikely. You begin to consider an intrinsic cause of myopathy, and order the following tests: a CMP, UA, thyroid-stimulating hormone, repeat CK, and vitamin D level. This testing reveals a vitamin D deficiency at 17 ng/ml (normal range: 30-74 ng/ml). You recommend vitamin D, 50,000 IU per week for 8 weeks. At follow-up, Ms. C's vitamin D level is 40. She says she feels better and her muscle complaints have resolved.

CORRESPONDENCE
Brent W. Smith, MD, Travis Air Force Base Family Medicine Residency, 101 Bodin Circle, Travis Air Force Base, CA 94535; smithb@smithnet.us

CASE › Marie C, a 75-year-old Asian woman, reports weakness in her legs and arms with unsteadiness when walking. She has a vague but persistent ache in her large muscles. Her symptoms have developed slowly over the past 3 months. She denies recent signs or symptoms of infection or other illness. Her medical history includes hypertension, hyperlipidemia, osteopenia, and obesity. Ms. C takes lisinopril 10 mg/d and atorvastatin, which was recently increased from 10 to 20 mg/d.

What would your next steps be in caring for this patient?

Patients who experience muscle-related symptoms such as pain, fatigue, or weakness often seek help from their family physician (FP). The list of possible causes of these complaints can be lengthy and vary greatly, from nonmyopathic conditions such as fibromyalgia to worrisome forms of myopathy such as inclusion body myositis or polymyositis. This article will help you to quickly identify which patients with muscle-related complaints should be evaluated for myopathy and what your work-up should include.

Myopathy or not?

Distinguishing between myopathy and nonmyopathic muscle pain or weakness is the first step in evaluating patients with muscle-related complaints. Many conditions share muscle-related symptoms, but actual muscle damage is not always present (eg, fibromyalgia, chronic pain, and chronic fatigue syndromes).¹ While there is some overlap in presentation between patients with myopathy and nonmyopathic conditions, there are important differences in symptoms, physical exam findings, and lab test results (TABLE 1^1-4). Notably, in myopathic disease, patients’ symptoms are usually progressive, vital signs are abnormal, and weakness is common, whereas patients with nonmyopathic disease typically have remitting and relapsing symptoms, normal vital signs, and no weakness.

Myopathy itself is divided into 3 categories—myositic, intrinsic, and toxic—which reflect the condition, or medication, that brought on the muscle damage (TABLE 2^2,4-15). Placing patients into one of these categories based on their risk factors, history, and physical exam findings can help to focus the diagnostic work-up on areas most likely to provide useful information.

Myositic myopathy can be caused by infection or autoimmunity

Myositic myopathies result in inflammatory destruction of muscle tissue. Patients with myositic myopathy often exhibit fever, malaise, weight loss, and general fatigue. Though weakness and pain are common, both can be variable or even absent in myositic myopathy.^2,5 Myositic myopathy can be caused by infectious agents or can develop from an autoimmune disease.

Infectious myositic myopathy is one of the more common types of myopathy that FPs will encounter.² Viruses such as influenza, parainfluenza, coxsackievirus, human immunodeficiency virus, cytomegalovirus, echovirus, adenovirus, Epstein-Barr, and hepatitis C are common causes.^2,4,16 Patients with 
a viral myositis often report prodromal symptoms such as fever, upper respiratory illness, or GI distress one to 2 weeks before the onset of muscle complaints. Bacterial and fungal myositides are relatively rare. Both most often occur as the result of penetrating trauma or immunocompromise, and are generally not subtle.² Parasitic myopathy can occur from the invasion of skeletal muscle by trichinella after ingesting undercooked, infected meat.² Although previously a more common problem, currently only 10 to 20 cases of trichinellosis are reported in the United States each year.¹⁷ Due to their rarity, bacterial, fungal, and parasitic myositides are not reviewed here.

Patients with a viral myositis often report prodromal symptoms such as fever, upper respiratory illness, or gastrointestinal distress one to 2 weeks before the onset of muscle complaints. Muscle pain is usually multifocal, involving larger, bilateral muscle groups, and may be associated with swelling.

Patients with viral myositis may exhibit diffusely painful, swollen, or boggy-feeling muscles as well as weakness and pain with exertion. Other signs of viral infection such as rash, fever, upper respiratory symptoms, or meningeal signs may be present. Severe signs include arrhythmia or respiratory failure due to cardiac muscle or diaphragm involvement, or signs of renal failure due to precipitation of myoglobin in the renal system (ie, rhabdomyolysis).² If the infection affects the heart, patients may develop palpitations, pleuritic chest pain, or shortness of breath.²

Diagnosis of viral myositis relies heavily on clinical suspicion in patients with a fitting history and physical exam findings. Helpful lab tests include a complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), creatine kinase (CK), and liver function tests (LFTs), all of which can be abnormal in viral myositis. Viral polymerase chain reaction, culture, or antigen testing may be helpful in severe or confusing cases, but in most cases such testing is unnecessary. Muscle biopsy is not recommended except in persistent cases, where definitive identification of the causative agent might alter treatment or when nonviral infection is suspected.²

Autoimmune myositic myopathy. Unlike infectious myopathies, autoimmune myopathies are usually chronic, subtle, and relatively rare. The 3 most common autoimmune myopathies—polymyositis, dermatomyositis, and inclusion body myositis—have a combined prevalence of approximately 10:100,000.⁶ Although these types of myopathies are uncommon, FPs will likely be the first to evaluate a patient with one of them.

Patients with an autoimmune myopathy typically complain of weakness and mild to moderate muscle pain, although pain may be absent. Compared to infectious myopathies, autoimmune myopathies usually exhibit a more indolent course. Patients with advanced disease may report fever, weight loss, shortness of breath from cardiomyopathy, heartburn from a weakened lower esophageal sphincter, and/or a rash.⁵

A patient
 with mild
 to moderate electrolyte problems may complain of muscle fatigue, weakness,
 or pain. Physical examination may reveal symmetric, proximal muscle weakness. Atrophy is typically not seen until late in the disease. Skin exam usually is normal in patients with inclusion body myositis and polymyositis. The typical rash of dermatomyositis is a heliotrope (blue-purple) discoloration on the upper eyelids and a raised, violaceous, scaly eruption on the knuckles (Gottron’s papules).

Laboratory tests that can be helpful include CK, lactate dehydrogenase (LDH), aldolase, and LFTs (reflecting muscle injury, not liver involvement). For polymyositis and dermatomyositis, CK is the most sensitive lab test and often exhibits the highest elevation above normal.⁶ Conversely, CK is often normal or only mildly elevated in inclusion body myositis. Up to 80% of patients with autoimmune myopathy will have antinuclear antibodies.^3,5 ESR and CRP levels are also often elevated.

Both electromyography (EMG) and muscle biopsy may be required to diagnose autoimmune myopathy, but these are typically done under the direction of a rheumatologist after an FP’s initial work-up is inconclusive.

Intrinsic myopathy: Suspect electrolyte problems, other causes

Intrinsic myopathy occurs in patients with electrolyte disorders, diseases of the endocrine system, or underlying metabolic dysfunction.

Electrolyte disorders. Muscle-related symptoms are unlikely to be the chief complaint of patients with severe electrolyte imbalance. However, a patient with mild to moderate electrolyte problems may develop muscle fatigue, weakness, or pain. TABLE 3 reviews other signs and symptoms of electrolyte abnormalities that may be helpful in establishing a diagnosis in a patient with muscle complaints.

Ordering a complete metabolic panel (CMP), CK, and urinalysis (UA) can help rule out electrolyte disorders. If electrolyte disorders are detected, an electrocardiogram is useful to evaluate for cardiac dysfunction. Once an electrolyte disorder is identified, investigate its underlying cause. Correcting the electrolyte disorder should help improve symptoms of myopathy.

Endocrine myopathy can be associated with hypothyroidism, hyperthyroidism, parathyroid disease, vitamin D deficiency, or Cushing syndrome.^8-10,18,19 Although less common than some other causes, identifying endocrine myopathy is crucial because correcting the underlying disease will often improve multiple aspects of the patient’s health.

The presentation of endocrine myopathy may be subtle. Patients with hypothyroidism may experience muscle pain or weakness, fatigue, cold sensitivity, constipation, and dry skin.²⁰ Muscle-related symptoms may be the only sign of endocrine myopathy in a patient who would otherwise be considered to have subclinical hypothyroidism.^8,18 Hyperthyroidism can present with weight loss, heat intolerance, frequent bowel movements, tachycardia, and muscle weakness.²¹

Patients with parathyroid disease— especially patients with chronic renal failure—may report proximal muscle weakness, often in the lower extremities.¹⁹ Complaints of muscle weakness or pain can occur with severe vitamin D deficiency.¹⁰ Patients with Cushing syndrome often experience proximal weakness and weight gain.⁹

Patients with a personal or family history of endocrine disorders, previous thyroid surgery, or those taking medications that can impair thyroid function, such as lithium, amiodarone, or interferon, are at risk for endocrine myopathy.^18-20 Suspect hyperparathyroidism in patients with chronic kidney disease who complain of weakness.

Vitamin D deficiency is relatively common, with at minimum 20% of elderly adults estimated to be deficient.¹⁰ Patients at risk for Cushing disease are most likely receiving pharmacologic doses of glucocorticoids, which can increase their risk of myopathy, or to have ectopic adrenocorticotropic hormone secretion.

Metabolic myopathy results from a lack of sufficient energy production in the muscle. The 3 main groups of metabolic myopathy are impaired muscle glycogenoses, disorders of fatty acid oxidation, and mitochondrial myopathies.⁷

Because metabolic myopathy can occur at any age, a thorough history and physical is crucial for diagnosis. Proximal weakness in metabolic myopathy is often associated with exercise intolerance, stressful illness, or fasting. Patients often present with dynamic abnormalities such as fatigue, muscle cramping, and even rhabdomyolysis during exertion.⁷

When evaluating patients you suspect may have metabolic myopathy, a physical exam may reveal muscle contractures, muscle swelling, or proximal muscle weakness. Patients with certain types of fatty acid oxidation disorders or mitochondrial disorders may also exhibit cardiomyopathy, neuropathy, retinopathy, ataxia, hearing loss, or other systemic manifestations.⁷

Basic labs for investigating suspected metabolic myopathy include serum electrolytes, glucose, LFTs, CK (which may or may not be elevated), lactate, ammonia, and UA for myoglobinuria. More advanced labs, such as serum total carnitine and acylcarnitine as well as urinary levels of dicarboxylic acids and acylglycines, may be needed if a metabolic disorder is strongly suspected.⁷ Muscle biopsy, EMG, and genetic testing can also prove helpful in diagnosis. Definitive diagnosis and treatment of metabolic myopathy usually requires a multidisciplinary team of providers, including subspecialty referral.

Toxic myopathy

The symptoms of drug-induced toxic myopathy are usually more insidious and lab abnormalities are usually more subtle than for other forms
 of myopathy. Toxic myopathy refers to muscle damage caused by an exogenous chemical agent, most often a drug. The mechanism of toxicity is not always clear and may result from the activation of inflammatory responses similar to autoimmune myopathy.²² Toxic myopathies may result from several commonly used medications; cholesterol-lowering medications are a common culprit.^13-15,23-25 Drug-induced myopathies vary in frequency and severity. For instance, in patients taking statins, the rate of myalgias is 6%, while the incidence of rhabdomyolysis is estimated to be 4 per 100,000, and is found most often in patients taking concomitant fibrates.²³

Drug-induced toxic myopathy differs from previously discussed myopathies in that symptoms are usually more insidious, findings on exam are more often mixed muscular and neurologic, and lab abnormalities are usually more subtle.^11,12 Symptoms of myopathy typically occur weeks or months after initiating a drug and usually improve or resolve within weeks after discontinuing the offending agent. Knowing the patient’s medication list and which medications cause certain patterns of myopathy symptoms can help guide the differential diagnosis (TABLE 4^11-15,22-25).

Cholesterol-lowering medications such as statins are a common cause of toxic myopathy. Risk factors for most medication-related myopathies are polypharmacy, renal or liver disease, and age over 50 years^13-15,23-25 The physical exam for patients with drug- or toxin-related myopathy will most often reveal relatively minor abnormalities such as muscle tenderness and mild weakness, except for the most severe or advanced cases. Most patients will not have physical signs that suggest an underlying illness. CK levels and LFTs should be obtained. Basic chemistry and UA may also be helpful in patients with risk factors for renal disease.

CASE › Ms. C has been taking a statin for more than 10 years, and the dose was recently increased. You are aware that statin-related muscle injury can develop even after years of use, and suspect the statin may be causing her myopathy. You order a CK test, which is mildly elevated. You recommend discontinuing the statin. After 8 weeks off her statin, Ms. C’s Symptoms do not improve. Given her lack of systemic complaints, myositic myopathy from an infectious or rheumatologic cause seems unlikely. You begin to consider an intrinsic cause of myopathy, and order the following tests: a CMP, UA, thyroid-stimulating hormone, repeat CK, and vitamin D level. This testing reveals a vitamin D deficiency at 17 ng/ml (normal range: 30-74 ng/ml). You recommend vitamin D, 50,000 IU per week for 8 weeks. At follow-up, Ms. C's vitamin D level is 40. She says she feels better and her muscle complaints have resolved.

CORRESPONDENCE
Brent W. Smith, MD, Travis Air Force Base Family Medicine Residency, 101 Bodin Circle, Travis Air Force Base, CA 94535; smithb@smithnet.us