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Myasthenia gravis: Finding strength in treatment options
The term myasthenia gravis (MG), from the Latin “grave muscle weakness,” denotes the rare autoimmune disorder characterized by dysfunction at the neuromuscular junction.1 The clinical presentation of the disease is variable but most often includes ocular symptoms, such as ptosis and diplopia, bulbar weakness, and muscle fatigue upon exertion.2,3 Severe symptoms can lead to myasthenic crisis, in which generalized weakness can affect respiratory muscles, leading to possible intubation or death.2,3
Onset of disease ranges from childhood to late adulthood, and largely depends on the subgroup of disease and the age of the patient.4 Although complications from MG can arise, treatment methods have considerably reduced the risk of MG-associated mortality, with the current rate estimated to be 0.06 to 0.89 deaths for every 1 million person-years (that is, approximately 5% of cases).3,5
Pathophysiology
MG is caused by binding of autoimmune antibodies to postsynaptic receptors and by molecules that prevent signal transduction at the muscle endplate.2,4,6,7 The main culprit behind the pathology (in approximately 85% of cases) is an autoimmune antibody for the acetylcholine receptor (AChR); however, other offending antibodies – against muscle-specific serine kinases (MuSK), low-density lipoprotein receptor-related protein 4 (LRP4), and the proteoglycan agrin – are known, although at a lower frequency (in approximately 15% of cases).4,8 These antibodies prevent signal transmission by blocking, destroying, or disrupting the clustering of AChR at the muscle endplate, a necessary step in formation of the neuromuscular junction.4,8,9
The activity of these antibodies is key to understanding the importance of subgrouping the types of MG on the basis of antigen-specific autoimmune interactions. Specifically, the four categories of disease following a diagnosis of MG2,7 are:
- AChR antibody-positive.
- MuSK antibody-positive.
- LRP4 antibody-positive.
- Seronegative MG.
Classifying MG into subgroups gives insight into the functional expectations and potential treatment options for a given patient, although expectations can vary.2
Regrettably, the well-understood pathophysiology, diagnosis, and prognosis of MG have limited investigation and development of new therapies. Additionally, mainstay treatments, such as thymectomy and prednisone, work to alleviate symptoms for most patients, and have also contributed to periods of slowed research and development. However, treatment of refractory MG has, in recent years, become the subject of research on new therapeutic options, aimed at treating heterogeneous disease populations.10
In this review, we discuss the diagnosis of, and treatment options for, MG, and provide an update on promising options in the therapeutic pipeline.
Diagnosis
Distinguishing MG from other neuromuscular junction disorders is a pertinent step before treatment. Although the biomarkers discussed in this section are sensitive for making a diagnosis of MG, additional research is needed to classify seronegative patients who do not have circulating autoantibodies that are pathognomonic for MG.11
Upon clinical examination of observable myasthenic weakness, next steps would require assays for anti-AChR and anti-MuSK.1 If either of those tests are inconclusive, assays for anti-LRP4 are available (although the LRP4 antibody is also a marker in other neurological disorders).12
In the MG diagnostic algorithm, next steps include an electromyography repetitive stimulation test, which, if inconclusive, is followed by single-fiber electromyography.1 If any of these tests return positive, computed tomography or magnetic resonance imaging is necessary for thymus screening.
What follows this diagnostic schema is pharmacotherapeutic or surgical intervention to reduce, or even eliminate, symptoms of MG.1
Consensus on treatment standards
A quantitative assessment of best options for treating MG was conducted by leading experts,13 who reached consensus that primary outcomes in treating MG are reached when a patient presents without symptoms or limitations on daily activities; or has only slight weakness or fatigue in some muscles.13
Pyridostigmine, an acetylcholinesterase inhibitor, is recommended as part of the initial treatment plan for MG patients. Pyridostigmine prevents normal breakdown of acetylcholine, thus increasing acetylcholine levels and allowing signal transmission at the neuromuscular junction.14 Not all patients reach the aforementioned treatment goals when taking pyridostigmine, however; some require corticosteroids or immunosuppressive agents, or both, in addition.
Steroids, such as prednisone and prednisolone, occupy the second line in MG patients because of their ability to produce a rapid response, availability, and economy.1,15 Initial dosages of these medications are gradually adjusted to a maintenance dosage and schedule, as tolerated, to maintain control of symptoms.15
In MG patients who are in respiratory crisis, it is recommended that high-dosage prednisone be given in conjunction with plasmapheresis or intravenous immunoglobulin (IVIg).15 When the response to steroids is inadequate, adverse effects cannot be tolerated, or the patient experiences symptomatic relapse, nonsteroidal immunosuppressive agents are started.
Immunosuppressives are used to weaken the immune response or block production of self-antibodies. Several agents have been identified for use in MG, including azathioprine and mycophenolate mofetil; their use is limited, however, by a lack of supporting evidence from randomized clinical trials or the potential for serious adverse effects.13
Referral and specialized treatments. Patients who are refractory to all the aforementioned treatments should be referred to a physician who is expert in the management of MG. At this point, treatment guidelines recommend chronic IVIg infusion or plasmapheresis, which removes complement, cytokines, and antibodies from the blood.14 Additionally, monoclonal antibody therapies, such as eculizumab, have been shown to have efficacy in severe, refractory AChR antibody–positive generalized MG.16
Thymectomy has been a mainstay and, sometimes, first-line treatment of MG for nearly 80 years.15 The thymus has largely been implicated in the immunopathology of AChR-positive MG. Models suggest that increased expression of inflammatory factors causes an imbalance among immune cells, resulting in lymphofollicular hyperplasia or thymoma.17
Despite the growing body of evidence implicating the thymus in the progression of MG, some patients and physicians are reluctant to proceed with surgical intervention. This could be due to a disparity in surgical treatment options offered by surgeons, and facilities, with varying experience or ability to conduct newer techniques. Minimally invasive approaches, such as video-assisted thoracoscopic surgery and robotic thymectomy, have been found to be superior to traditional open surgical techniques.18,19 Minimally invasive techniques result in significantly fewer postoperative complications, less blood loss, and shorter length of hospital stay.19
In addition to the reduced risk offered by newer operative techniques, thymectomy has also been shown to have a beneficial effect by allowing the dosage of prednisone to be reduced in MG patients. In a randomized clinical trial conducted by Wolfe and coworkers,20 thymectomy produced improvement in two endpoints after 3 years in patients with nonthymomatous MG: the Quantitative MG Score and a lower average prednisone dosage. Although thymectomy is not a necessary precursor to remission in MG patients, it is still pertinent in reducing the adverse effects of long-term steroid use – providing objective evidence to support thymectomy as a treatment option.
Emerging therapies
Although conventional treatments for MG are well-established, 10% to 20% of MG patients remain refractory to therapeutic intervention.21 These patients are more susceptible to myasthenic crisis, which can result in hospitalization, intubation, and death.21 As mentioned, rescue therapies, including plasmapheresis and IVIg, are imperative to achieve remission of refractory MG, but such remission is unsustainable. Risks associated with these therapies, including contraindications and patient comorbidity, and their limited availability have prevented plasmapheresis and IVIg from being reliable interventions.12
These shortcomings, along with promising results from randomized clinical trials of newer modes of pharmacotherapeutic intervention, have increased interest in new therapies for MG. For example, complement pathway and neonatal Fc receptor (FcRn) inhibitors have recently shown promise in removing pathogenic autoimmune antibodies.18
Efgartigimod. FcRn is of interest in treating generalized MG because of its capacity to recycle and extend the half-life of IgG.22 Efgartigimod is a high-affinity FcRn inhibitor that simultaneously reduces IgG recycling and increases its degradation.22 This therapy is unique: it is highly selective for IgG, whereas other FcRn therapies are nonspecific, causing an undesirable decrease in other immunoglobulin and albumin levels.22 In December 2021, the Food and Drug Administration approved efgartigimod for the treatment of AChR-positive generalized MG.23
Zilucoplan is a subcutaneously administered complement inhibitor that has completed phase 3 clinical trials.18,24 The drug works by inhibiting cleavage of proteins C5a and C5b in the terminal complement complex, a necessary step in forming cytotoxic pores on targeted cells.18,24 Zilucoplan also prevents tissue damage and destruction of signal transmission at the postsynaptic membrane.25 Clinical trials have already established improvement in the Quantitative MG Score and the Myasthenia Gravis Activities of Daily Living Score in patients with generalized MG.18,24
Zilucoplan is similar to eculizumab, but targets a different binding site, allowing for treatment of heterogeneous MG populations who have a mutation in the eculizumab target antigen.26 Additionally, due to specific drug-body interactions, parameters for treatment using zilucoplan are broader than for therapies such as eculizumab. In a Zilucoplan press-release, the complement inhibitor showed statistically significant improvement in the treatment group of generalized, AChR-positive MG patients compared to the placebo group. Tolerability and safety was also a favorable finding in this study. However, a similar rate of treatment-emergent adverse events were recorded between the treatment group (76.7%) and placebo group (70.5%) which could indicate that the clinical application of this treatment is still forthcoming.27 If zilucoplan is approved by the FDA, it will be used earlier in disease progression and for a larger subset of patients.26
Nipocalimab is another immunoglobulin G1, FcRn antibody that reduces IgG levels in blood.27,28 A phase 2 clinical study in patients with AChR-positive or MuSK antibody–associated MG showed that 52% of patients who received nipocalimab had a significant reduction in the Myasthenia Gravis Activities of Daily Living Score 4 weeks after infusion.28 Phase 3 studies for adults with generalized MG are underway and are expected to conclude in April 2026.29
Looking forward
Despite emerging therapies aimed at treating IgG in both refractory and nonrefractory MG, there is still a need for research into biomarkers that further differentiate disease. Developing research into new biomarkers, such as circulating microRNAs, gives insight into the promise of personalized medicine, which can shape the landscape of MG and other disorders.30 As of August 2022, only two clinical trials are slated for investigation into new biomarkers for MG.
Although the treatment of MG might have once been considered stagnant, newer expert consensus and novel research are generating optimism for innovative therapies in coming years.
Mr. van der Eb is a second-year candidate in the master’s of science in applied life sciences program, Keck Graduate Institute, Claremont, Calif.; he has an associate’s degree in natural sciences from Pasadena City College, Calif., and a bachelor’s degree in biological sciences from the University of California, Irvine. Ms. Toruno is a graduate from the master’s of science in applied life sciences program, Keck Graduate Institute; she has a bachelor’s degree in psychology, with a minor in biological sciences, from the University of California, Irvine. Dr. Laird is director of clinical education and professor of practice for the master’s of science in physician assistant studies program, Keck Graduate Institute; he practices clinically in general and thoracic surgery.
References
1. Gilhus NE et al. Myasthenia gravis. Nat Rev Dis Primers. 2019 May 2;5(1):30. doi: 10.1038/s41572-019-0079-y.
2. Gilhus NE, Verschuuren JJ. Myasthenia gravis: Subgroup classification and therapeutic strategies. Lancet Neurol. 2015 Oct;14(10):1023-36. doi: 10.1016/S1474-4422(15)00145-3.
3. Dresser L et al. Myasthenia gravis: Epidemiology, pathophysiology and clinical manifestations. J Clin Med. 2021 May;10(11):2235. doi: 10.3390/jcm10112235.
4. Iyer SR et al. The neuromuscular junction: Roles in aging and neuromuscular disease. Int J Mol Sci. 2021 Jul;22(15):8058. doi: 10.3390/ijms22158058.
5. Hehir MK, Silvestri NJ. Generalized myasthenia gravis: Classification, clinical presentation, natural history, and epidemiology. Neurol Clin. 2018 May;36(2):253-60. doi: 10.1016/j.ncl.2018.01.002.
6. Prüss H. Autoantibodies in neurological disease. Nat Rev Immunol. 2021 Dec;21(12):798-813. doi: 10.1038/s41577-021-00543-w.
7. Drachman DB et al. Myasthenic antibodies cross-link acetylcholine receptors to accelerate degradation. N Engl J Med. 1978 May 18;298(20):1116-22. doi: 10.1056/NEJM197805182982004.
8. Meriggioli MN. Myasthenia gravis with anti-acetylcholine receptor antibodies. Front Neurol Neurosci. 2009;26:94-108. doi: 10.1159/000212371.
9. Zhang HL, Peng HB. Mechanism of acetylcholine receptor cluster formation induced by DC electric field. PLoS One. 2011;6(10):e26805. doi: 10.1371/journal.pone.0026805.
10. Fichtner ML et al. Autoimmune pathology in myasthenia gravis disease subtypes is governed by divergent mechanisms of immunopathology. Front Immunol. 2020 May 27;11:776. doi: 10.3389/fimmu.2020.00776.
11. Tzartos JS et al. LRP4 antibodies in serum and CSF from amyotrophic lateral sclerosis patients. Ann Clin Transl Neurol. 2014 Feb;1(2):80-87. doi: 10.1002/acn3.26.
12. Narayanaswami P et al. International consensus guidance for management of myasthenia gravis: 2020 update. Neurology. 2021;96(3):114-22. doi: 10.1212/WNL.0000000000011124.
13. Cortés-Vicente E et al. Myasthenia gravis treatment updates. Curr Treat Options Neurol. 2020 Jul 15;22(8):24. doi: 10.1007/s11940-020-00632-6.
14. Tannemaat MR, Verschuuren JJGM. Emerging therapies for autoimmune myasthenia gravis: Towards treatment without corticosteroids. Neuromuscul Disord. 2020 Feb;30(2):111-9. doi: 10.1016/j.nmd.2019.12.003.
15. Silvestri NJ, Wolfe GI. Treatment-refractory myasthenia gravis. J Clin Neuromuscul Dis. 2014 Jun;15(4):167-78. doi: 10.1097/CND.0000000000000034.
16. Sanders DB et al. International consensus guidance for management of myasthenia gravis: Executive summary. Neurology. 2016 Jul 26;87(4):419-25. doi: 10.1212/WNL.0000000000002790.
17. Evoli A, Meacci E. An update on thymectomy in myasthenia gravis. Expert Rev Neurother. 2019 Sep;19(9):823-33. doi: 10.1080/14737175.2019.1600404.
18. Habib AA et al. Update on immune-mediated therapies for myasthenia gravis. Muscle Nerve. 2020 Nov;62(5):579-92. doi: 10.1002/mus.26919.
19. O’Sullivan KE et al. A systematic review of robotic versus open and video assisted thoracoscopic surgery (VATS) approaches for thymectomy. Ann Cardiothorac Surg. 2019 Mar;8(2):174-93. doi: 10.21037/acs.2019.02.04.
20. Wolfe GI et al; MGTX Study Group. Randomized trial of thymectomy in myasthenia gravis. N Engl J Med. 2016;375(6):511-22. doi: 10.1056/NEJMoa1602489.
21. Schneider-Gold C et al. Understanding the burden of refractory myasthenia gravis. Ther Adv Neurol Disord. 2019 Mar 1;12:1756286419832242. doi: 10.1177/1756286419832242.
22. Howard JF Jr et al; . Safety, efficacy, and tolerability of efgartigimod in patients with generalised myasthenia gravis (ADAPT): A multicentre, randomised, placebo-controlled, phase 3 trial. Lancet Neurol. 2021 Jul;20(7):526-36. doi: 10.1016/S1474-4422(21)00159-9.
23. U.S. Food and Drug Administration. FDA approves new treatment for myasthenia gravis. News release. Dec 17, 2021. Accessed Feb 21, 2022. http://www.fda.gov/news-events/press-announcements/fda-approves-new-treatment-myasthenia-gravis.
24. Ra Pharmaceuticals. A phase 3, multicenter, randomized, double blind, placebo-controlled study to confirm the safety, tolerability, and efficacy of zilucoplan in subjects with generalized myasthenia gravis. ClinicalTrials.gov Identifier: NCT04115293. Updated Jan 28, 2022. Accessed Feb 21, 2022. https://clinicaltrials.gov/ct2/show/NCT04115293.
25. Howard JF Jr et al. Zilucoplan: An investigational complement C5 inhibitor for the treatment of acetylcholine receptor autoantibody–positive generalized myasthenia gravis. Expert Opin Investig Drugs. 2021 May;30(5):483-93. doi: 10.1080/13543784.2021.1897567.
26. Albazli K et al. Complement inhibitor therapy for myasthenia gravis. Front Immunol. 2020 Jun 3;11:917. doi: 10.3389/fimmu.2020.00917.
27. UCB announces positive Phase 3 results for rozanolixizumab in generalized myasthenia gravis. UCB press release. December 10. 2021. Accessed August 15, 2022. https://www.ucb.com/stories-media/Press-Releases/article/UCB-announces-positive-Phase-3-results-for-rozanolixizumab-in-generalized-myasthenia-gravis.
28. Keller CW et al. Fc-receptor targeted therapies for the treatment of myasthenia gravis. Int J Mol Sci. 2021 May;22(11):5755. doi: 10.3390/ijms22115755.
29. Janssen Research & Development LLC. Phase 3, multicenter, randomized, double-blind, placebo-controlled study to evaluate the efficacy, safety, pharmacokinetics, and pharmacodynamics of nipocalimab administered to adults with generalized myasthenia gravis. ClinicalTrials.gov Identifier: NCT04951622. Updated Feb 17, 2022. Accessed Feb 21, 2022. https://clinicaltrials.gov/ct2/show/NCT04951622.
30. Sabre L et al. Circulating miRNAs as potential biomarkers in myasthenia gravis: Tools for personalized medicine. Front Immunol. 2020 Mar 4;11:213. doi: 10.3389/fimmu.2020.00213.
The term myasthenia gravis (MG), from the Latin “grave muscle weakness,” denotes the rare autoimmune disorder characterized by dysfunction at the neuromuscular junction.1 The clinical presentation of the disease is variable but most often includes ocular symptoms, such as ptosis and diplopia, bulbar weakness, and muscle fatigue upon exertion.2,3 Severe symptoms can lead to myasthenic crisis, in which generalized weakness can affect respiratory muscles, leading to possible intubation or death.2,3
Onset of disease ranges from childhood to late adulthood, and largely depends on the subgroup of disease and the age of the patient.4 Although complications from MG can arise, treatment methods have considerably reduced the risk of MG-associated mortality, with the current rate estimated to be 0.06 to 0.89 deaths for every 1 million person-years (that is, approximately 5% of cases).3,5
Pathophysiology
MG is caused by binding of autoimmune antibodies to postsynaptic receptors and by molecules that prevent signal transduction at the muscle endplate.2,4,6,7 The main culprit behind the pathology (in approximately 85% of cases) is an autoimmune antibody for the acetylcholine receptor (AChR); however, other offending antibodies – against muscle-specific serine kinases (MuSK), low-density lipoprotein receptor-related protein 4 (LRP4), and the proteoglycan agrin – are known, although at a lower frequency (in approximately 15% of cases).4,8 These antibodies prevent signal transmission by blocking, destroying, or disrupting the clustering of AChR at the muscle endplate, a necessary step in formation of the neuromuscular junction.4,8,9
The activity of these antibodies is key to understanding the importance of subgrouping the types of MG on the basis of antigen-specific autoimmune interactions. Specifically, the four categories of disease following a diagnosis of MG2,7 are:
- AChR antibody-positive.
- MuSK antibody-positive.
- LRP4 antibody-positive.
- Seronegative MG.
Classifying MG into subgroups gives insight into the functional expectations and potential treatment options for a given patient, although expectations can vary.2
Regrettably, the well-understood pathophysiology, diagnosis, and prognosis of MG have limited investigation and development of new therapies. Additionally, mainstay treatments, such as thymectomy and prednisone, work to alleviate symptoms for most patients, and have also contributed to periods of slowed research and development. However, treatment of refractory MG has, in recent years, become the subject of research on new therapeutic options, aimed at treating heterogeneous disease populations.10
In this review, we discuss the diagnosis of, and treatment options for, MG, and provide an update on promising options in the therapeutic pipeline.
Diagnosis
Distinguishing MG from other neuromuscular junction disorders is a pertinent step before treatment. Although the biomarkers discussed in this section are sensitive for making a diagnosis of MG, additional research is needed to classify seronegative patients who do not have circulating autoantibodies that are pathognomonic for MG.11
Upon clinical examination of observable myasthenic weakness, next steps would require assays for anti-AChR and anti-MuSK.1 If either of those tests are inconclusive, assays for anti-LRP4 are available (although the LRP4 antibody is also a marker in other neurological disorders).12
In the MG diagnostic algorithm, next steps include an electromyography repetitive stimulation test, which, if inconclusive, is followed by single-fiber electromyography.1 If any of these tests return positive, computed tomography or magnetic resonance imaging is necessary for thymus screening.
What follows this diagnostic schema is pharmacotherapeutic or surgical intervention to reduce, or even eliminate, symptoms of MG.1
Consensus on treatment standards
A quantitative assessment of best options for treating MG was conducted by leading experts,13 who reached consensus that primary outcomes in treating MG are reached when a patient presents without symptoms or limitations on daily activities; or has only slight weakness or fatigue in some muscles.13
Pyridostigmine, an acetylcholinesterase inhibitor, is recommended as part of the initial treatment plan for MG patients. Pyridostigmine prevents normal breakdown of acetylcholine, thus increasing acetylcholine levels and allowing signal transmission at the neuromuscular junction.14 Not all patients reach the aforementioned treatment goals when taking pyridostigmine, however; some require corticosteroids or immunosuppressive agents, or both, in addition.
Steroids, such as prednisone and prednisolone, occupy the second line in MG patients because of their ability to produce a rapid response, availability, and economy.1,15 Initial dosages of these medications are gradually adjusted to a maintenance dosage and schedule, as tolerated, to maintain control of symptoms.15
In MG patients who are in respiratory crisis, it is recommended that high-dosage prednisone be given in conjunction with plasmapheresis or intravenous immunoglobulin (IVIg).15 When the response to steroids is inadequate, adverse effects cannot be tolerated, or the patient experiences symptomatic relapse, nonsteroidal immunosuppressive agents are started.
Immunosuppressives are used to weaken the immune response or block production of self-antibodies. Several agents have been identified for use in MG, including azathioprine and mycophenolate mofetil; their use is limited, however, by a lack of supporting evidence from randomized clinical trials or the potential for serious adverse effects.13
Referral and specialized treatments. Patients who are refractory to all the aforementioned treatments should be referred to a physician who is expert in the management of MG. At this point, treatment guidelines recommend chronic IVIg infusion or plasmapheresis, which removes complement, cytokines, and antibodies from the blood.14 Additionally, monoclonal antibody therapies, such as eculizumab, have been shown to have efficacy in severe, refractory AChR antibody–positive generalized MG.16
Thymectomy has been a mainstay and, sometimes, first-line treatment of MG for nearly 80 years.15 The thymus has largely been implicated in the immunopathology of AChR-positive MG. Models suggest that increased expression of inflammatory factors causes an imbalance among immune cells, resulting in lymphofollicular hyperplasia or thymoma.17
Despite the growing body of evidence implicating the thymus in the progression of MG, some patients and physicians are reluctant to proceed with surgical intervention. This could be due to a disparity in surgical treatment options offered by surgeons, and facilities, with varying experience or ability to conduct newer techniques. Minimally invasive approaches, such as video-assisted thoracoscopic surgery and robotic thymectomy, have been found to be superior to traditional open surgical techniques.18,19 Minimally invasive techniques result in significantly fewer postoperative complications, less blood loss, and shorter length of hospital stay.19
In addition to the reduced risk offered by newer operative techniques, thymectomy has also been shown to have a beneficial effect by allowing the dosage of prednisone to be reduced in MG patients. In a randomized clinical trial conducted by Wolfe and coworkers,20 thymectomy produced improvement in two endpoints after 3 years in patients with nonthymomatous MG: the Quantitative MG Score and a lower average prednisone dosage. Although thymectomy is not a necessary precursor to remission in MG patients, it is still pertinent in reducing the adverse effects of long-term steroid use – providing objective evidence to support thymectomy as a treatment option.
Emerging therapies
Although conventional treatments for MG are well-established, 10% to 20% of MG patients remain refractory to therapeutic intervention.21 These patients are more susceptible to myasthenic crisis, which can result in hospitalization, intubation, and death.21 As mentioned, rescue therapies, including plasmapheresis and IVIg, are imperative to achieve remission of refractory MG, but such remission is unsustainable. Risks associated with these therapies, including contraindications and patient comorbidity, and their limited availability have prevented plasmapheresis and IVIg from being reliable interventions.12
These shortcomings, along with promising results from randomized clinical trials of newer modes of pharmacotherapeutic intervention, have increased interest in new therapies for MG. For example, complement pathway and neonatal Fc receptor (FcRn) inhibitors have recently shown promise in removing pathogenic autoimmune antibodies.18
Efgartigimod. FcRn is of interest in treating generalized MG because of its capacity to recycle and extend the half-life of IgG.22 Efgartigimod is a high-affinity FcRn inhibitor that simultaneously reduces IgG recycling and increases its degradation.22 This therapy is unique: it is highly selective for IgG, whereas other FcRn therapies are nonspecific, causing an undesirable decrease in other immunoglobulin and albumin levels.22 In December 2021, the Food and Drug Administration approved efgartigimod for the treatment of AChR-positive generalized MG.23
Zilucoplan is a subcutaneously administered complement inhibitor that has completed phase 3 clinical trials.18,24 The drug works by inhibiting cleavage of proteins C5a and C5b in the terminal complement complex, a necessary step in forming cytotoxic pores on targeted cells.18,24 Zilucoplan also prevents tissue damage and destruction of signal transmission at the postsynaptic membrane.25 Clinical trials have already established improvement in the Quantitative MG Score and the Myasthenia Gravis Activities of Daily Living Score in patients with generalized MG.18,24
Zilucoplan is similar to eculizumab, but targets a different binding site, allowing for treatment of heterogeneous MG populations who have a mutation in the eculizumab target antigen.26 Additionally, due to specific drug-body interactions, parameters for treatment using zilucoplan are broader than for therapies such as eculizumab. In a Zilucoplan press-release, the complement inhibitor showed statistically significant improvement in the treatment group of generalized, AChR-positive MG patients compared to the placebo group. Tolerability and safety was also a favorable finding in this study. However, a similar rate of treatment-emergent adverse events were recorded between the treatment group (76.7%) and placebo group (70.5%) which could indicate that the clinical application of this treatment is still forthcoming.27 If zilucoplan is approved by the FDA, it will be used earlier in disease progression and for a larger subset of patients.26
Nipocalimab is another immunoglobulin G1, FcRn antibody that reduces IgG levels in blood.27,28 A phase 2 clinical study in patients with AChR-positive or MuSK antibody–associated MG showed that 52% of patients who received nipocalimab had a significant reduction in the Myasthenia Gravis Activities of Daily Living Score 4 weeks after infusion.28 Phase 3 studies for adults with generalized MG are underway and are expected to conclude in April 2026.29
Looking forward
Despite emerging therapies aimed at treating IgG in both refractory and nonrefractory MG, there is still a need for research into biomarkers that further differentiate disease. Developing research into new biomarkers, such as circulating microRNAs, gives insight into the promise of personalized medicine, which can shape the landscape of MG and other disorders.30 As of August 2022, only two clinical trials are slated for investigation into new biomarkers for MG.
Although the treatment of MG might have once been considered stagnant, newer expert consensus and novel research are generating optimism for innovative therapies in coming years.
Mr. van der Eb is a second-year candidate in the master’s of science in applied life sciences program, Keck Graduate Institute, Claremont, Calif.; he has an associate’s degree in natural sciences from Pasadena City College, Calif., and a bachelor’s degree in biological sciences from the University of California, Irvine. Ms. Toruno is a graduate from the master’s of science in applied life sciences program, Keck Graduate Institute; she has a bachelor’s degree in psychology, with a minor in biological sciences, from the University of California, Irvine. Dr. Laird is director of clinical education and professor of practice for the master’s of science in physician assistant studies program, Keck Graduate Institute; he practices clinically in general and thoracic surgery.
References
1. Gilhus NE et al. Myasthenia gravis. Nat Rev Dis Primers. 2019 May 2;5(1):30. doi: 10.1038/s41572-019-0079-y.
2. Gilhus NE, Verschuuren JJ. Myasthenia gravis: Subgroup classification and therapeutic strategies. Lancet Neurol. 2015 Oct;14(10):1023-36. doi: 10.1016/S1474-4422(15)00145-3.
3. Dresser L et al. Myasthenia gravis: Epidemiology, pathophysiology and clinical manifestations. J Clin Med. 2021 May;10(11):2235. doi: 10.3390/jcm10112235.
4. Iyer SR et al. The neuromuscular junction: Roles in aging and neuromuscular disease. Int J Mol Sci. 2021 Jul;22(15):8058. doi: 10.3390/ijms22158058.
5. Hehir MK, Silvestri NJ. Generalized myasthenia gravis: Classification, clinical presentation, natural history, and epidemiology. Neurol Clin. 2018 May;36(2):253-60. doi: 10.1016/j.ncl.2018.01.002.
6. Prüss H. Autoantibodies in neurological disease. Nat Rev Immunol. 2021 Dec;21(12):798-813. doi: 10.1038/s41577-021-00543-w.
7. Drachman DB et al. Myasthenic antibodies cross-link acetylcholine receptors to accelerate degradation. N Engl J Med. 1978 May 18;298(20):1116-22. doi: 10.1056/NEJM197805182982004.
8. Meriggioli MN. Myasthenia gravis with anti-acetylcholine receptor antibodies. Front Neurol Neurosci. 2009;26:94-108. doi: 10.1159/000212371.
9. Zhang HL, Peng HB. Mechanism of acetylcholine receptor cluster formation induced by DC electric field. PLoS One. 2011;6(10):e26805. doi: 10.1371/journal.pone.0026805.
10. Fichtner ML et al. Autoimmune pathology in myasthenia gravis disease subtypes is governed by divergent mechanisms of immunopathology. Front Immunol. 2020 May 27;11:776. doi: 10.3389/fimmu.2020.00776.
11. Tzartos JS et al. LRP4 antibodies in serum and CSF from amyotrophic lateral sclerosis patients. Ann Clin Transl Neurol. 2014 Feb;1(2):80-87. doi: 10.1002/acn3.26.
12. Narayanaswami P et al. International consensus guidance for management of myasthenia gravis: 2020 update. Neurology. 2021;96(3):114-22. doi: 10.1212/WNL.0000000000011124.
13. Cortés-Vicente E et al. Myasthenia gravis treatment updates. Curr Treat Options Neurol. 2020 Jul 15;22(8):24. doi: 10.1007/s11940-020-00632-6.
14. Tannemaat MR, Verschuuren JJGM. Emerging therapies for autoimmune myasthenia gravis: Towards treatment without corticosteroids. Neuromuscul Disord. 2020 Feb;30(2):111-9. doi: 10.1016/j.nmd.2019.12.003.
15. Silvestri NJ, Wolfe GI. Treatment-refractory myasthenia gravis. J Clin Neuromuscul Dis. 2014 Jun;15(4):167-78. doi: 10.1097/CND.0000000000000034.
16. Sanders DB et al. International consensus guidance for management of myasthenia gravis: Executive summary. Neurology. 2016 Jul 26;87(4):419-25. doi: 10.1212/WNL.0000000000002790.
17. Evoli A, Meacci E. An update on thymectomy in myasthenia gravis. Expert Rev Neurother. 2019 Sep;19(9):823-33. doi: 10.1080/14737175.2019.1600404.
18. Habib AA et al. Update on immune-mediated therapies for myasthenia gravis. Muscle Nerve. 2020 Nov;62(5):579-92. doi: 10.1002/mus.26919.
19. O’Sullivan KE et al. A systematic review of robotic versus open and video assisted thoracoscopic surgery (VATS) approaches for thymectomy. Ann Cardiothorac Surg. 2019 Mar;8(2):174-93. doi: 10.21037/acs.2019.02.04.
20. Wolfe GI et al; MGTX Study Group. Randomized trial of thymectomy in myasthenia gravis. N Engl J Med. 2016;375(6):511-22. doi: 10.1056/NEJMoa1602489.
21. Schneider-Gold C et al. Understanding the burden of refractory myasthenia gravis. Ther Adv Neurol Disord. 2019 Mar 1;12:1756286419832242. doi: 10.1177/1756286419832242.
22. Howard JF Jr et al; . Safety, efficacy, and tolerability of efgartigimod in patients with generalised myasthenia gravis (ADAPT): A multicentre, randomised, placebo-controlled, phase 3 trial. Lancet Neurol. 2021 Jul;20(7):526-36. doi: 10.1016/S1474-4422(21)00159-9.
23. U.S. Food and Drug Administration. FDA approves new treatment for myasthenia gravis. News release. Dec 17, 2021. Accessed Feb 21, 2022. http://www.fda.gov/news-events/press-announcements/fda-approves-new-treatment-myasthenia-gravis.
24. Ra Pharmaceuticals. A phase 3, multicenter, randomized, double blind, placebo-controlled study to confirm the safety, tolerability, and efficacy of zilucoplan in subjects with generalized myasthenia gravis. ClinicalTrials.gov Identifier: NCT04115293. Updated Jan 28, 2022. Accessed Feb 21, 2022. https://clinicaltrials.gov/ct2/show/NCT04115293.
25. Howard JF Jr et al. Zilucoplan: An investigational complement C5 inhibitor for the treatment of acetylcholine receptor autoantibody–positive generalized myasthenia gravis. Expert Opin Investig Drugs. 2021 May;30(5):483-93. doi: 10.1080/13543784.2021.1897567.
26. Albazli K et al. Complement inhibitor therapy for myasthenia gravis. Front Immunol. 2020 Jun 3;11:917. doi: 10.3389/fimmu.2020.00917.
27. UCB announces positive Phase 3 results for rozanolixizumab in generalized myasthenia gravis. UCB press release. December 10. 2021. Accessed August 15, 2022. https://www.ucb.com/stories-media/Press-Releases/article/UCB-announces-positive-Phase-3-results-for-rozanolixizumab-in-generalized-myasthenia-gravis.
28. Keller CW et al. Fc-receptor targeted therapies for the treatment of myasthenia gravis. Int J Mol Sci. 2021 May;22(11):5755. doi: 10.3390/ijms22115755.
29. Janssen Research & Development LLC. Phase 3, multicenter, randomized, double-blind, placebo-controlled study to evaluate the efficacy, safety, pharmacokinetics, and pharmacodynamics of nipocalimab administered to adults with generalized myasthenia gravis. ClinicalTrials.gov Identifier: NCT04951622. Updated Feb 17, 2022. Accessed Feb 21, 2022. https://clinicaltrials.gov/ct2/show/NCT04951622.
30. Sabre L et al. Circulating miRNAs as potential biomarkers in myasthenia gravis: Tools for personalized medicine. Front Immunol. 2020 Mar 4;11:213. doi: 10.3389/fimmu.2020.00213.
The term myasthenia gravis (MG), from the Latin “grave muscle weakness,” denotes the rare autoimmune disorder characterized by dysfunction at the neuromuscular junction.1 The clinical presentation of the disease is variable but most often includes ocular symptoms, such as ptosis and diplopia, bulbar weakness, and muscle fatigue upon exertion.2,3 Severe symptoms can lead to myasthenic crisis, in which generalized weakness can affect respiratory muscles, leading to possible intubation or death.2,3
Onset of disease ranges from childhood to late adulthood, and largely depends on the subgroup of disease and the age of the patient.4 Although complications from MG can arise, treatment methods have considerably reduced the risk of MG-associated mortality, with the current rate estimated to be 0.06 to 0.89 deaths for every 1 million person-years (that is, approximately 5% of cases).3,5
Pathophysiology
MG is caused by binding of autoimmune antibodies to postsynaptic receptors and by molecules that prevent signal transduction at the muscle endplate.2,4,6,7 The main culprit behind the pathology (in approximately 85% of cases) is an autoimmune antibody for the acetylcholine receptor (AChR); however, other offending antibodies – against muscle-specific serine kinases (MuSK), low-density lipoprotein receptor-related protein 4 (LRP4), and the proteoglycan agrin – are known, although at a lower frequency (in approximately 15% of cases).4,8 These antibodies prevent signal transmission by blocking, destroying, or disrupting the clustering of AChR at the muscle endplate, a necessary step in formation of the neuromuscular junction.4,8,9
The activity of these antibodies is key to understanding the importance of subgrouping the types of MG on the basis of antigen-specific autoimmune interactions. Specifically, the four categories of disease following a diagnosis of MG2,7 are:
- AChR antibody-positive.
- MuSK antibody-positive.
- LRP4 antibody-positive.
- Seronegative MG.
Classifying MG into subgroups gives insight into the functional expectations and potential treatment options for a given patient, although expectations can vary.2
Regrettably, the well-understood pathophysiology, diagnosis, and prognosis of MG have limited investigation and development of new therapies. Additionally, mainstay treatments, such as thymectomy and prednisone, work to alleviate symptoms for most patients, and have also contributed to periods of slowed research and development. However, treatment of refractory MG has, in recent years, become the subject of research on new therapeutic options, aimed at treating heterogeneous disease populations.10
In this review, we discuss the diagnosis of, and treatment options for, MG, and provide an update on promising options in the therapeutic pipeline.
Diagnosis
Distinguishing MG from other neuromuscular junction disorders is a pertinent step before treatment. Although the biomarkers discussed in this section are sensitive for making a diagnosis of MG, additional research is needed to classify seronegative patients who do not have circulating autoantibodies that are pathognomonic for MG.11
Upon clinical examination of observable myasthenic weakness, next steps would require assays for anti-AChR and anti-MuSK.1 If either of those tests are inconclusive, assays for anti-LRP4 are available (although the LRP4 antibody is also a marker in other neurological disorders).12
In the MG diagnostic algorithm, next steps include an electromyography repetitive stimulation test, which, if inconclusive, is followed by single-fiber electromyography.1 If any of these tests return positive, computed tomography or magnetic resonance imaging is necessary for thymus screening.
What follows this diagnostic schema is pharmacotherapeutic or surgical intervention to reduce, or even eliminate, symptoms of MG.1
Consensus on treatment standards
A quantitative assessment of best options for treating MG was conducted by leading experts,13 who reached consensus that primary outcomes in treating MG are reached when a patient presents without symptoms or limitations on daily activities; or has only slight weakness or fatigue in some muscles.13
Pyridostigmine, an acetylcholinesterase inhibitor, is recommended as part of the initial treatment plan for MG patients. Pyridostigmine prevents normal breakdown of acetylcholine, thus increasing acetylcholine levels and allowing signal transmission at the neuromuscular junction.14 Not all patients reach the aforementioned treatment goals when taking pyridostigmine, however; some require corticosteroids or immunosuppressive agents, or both, in addition.
Steroids, such as prednisone and prednisolone, occupy the second line in MG patients because of their ability to produce a rapid response, availability, and economy.1,15 Initial dosages of these medications are gradually adjusted to a maintenance dosage and schedule, as tolerated, to maintain control of symptoms.15
In MG patients who are in respiratory crisis, it is recommended that high-dosage prednisone be given in conjunction with plasmapheresis or intravenous immunoglobulin (IVIg).15 When the response to steroids is inadequate, adverse effects cannot be tolerated, or the patient experiences symptomatic relapse, nonsteroidal immunosuppressive agents are started.
Immunosuppressives are used to weaken the immune response or block production of self-antibodies. Several agents have been identified for use in MG, including azathioprine and mycophenolate mofetil; their use is limited, however, by a lack of supporting evidence from randomized clinical trials or the potential for serious adverse effects.13
Referral and specialized treatments. Patients who are refractory to all the aforementioned treatments should be referred to a physician who is expert in the management of MG. At this point, treatment guidelines recommend chronic IVIg infusion or plasmapheresis, which removes complement, cytokines, and antibodies from the blood.14 Additionally, monoclonal antibody therapies, such as eculizumab, have been shown to have efficacy in severe, refractory AChR antibody–positive generalized MG.16
Thymectomy has been a mainstay and, sometimes, first-line treatment of MG for nearly 80 years.15 The thymus has largely been implicated in the immunopathology of AChR-positive MG. Models suggest that increased expression of inflammatory factors causes an imbalance among immune cells, resulting in lymphofollicular hyperplasia or thymoma.17
Despite the growing body of evidence implicating the thymus in the progression of MG, some patients and physicians are reluctant to proceed with surgical intervention. This could be due to a disparity in surgical treatment options offered by surgeons, and facilities, with varying experience or ability to conduct newer techniques. Minimally invasive approaches, such as video-assisted thoracoscopic surgery and robotic thymectomy, have been found to be superior to traditional open surgical techniques.18,19 Minimally invasive techniques result in significantly fewer postoperative complications, less blood loss, and shorter length of hospital stay.19
In addition to the reduced risk offered by newer operative techniques, thymectomy has also been shown to have a beneficial effect by allowing the dosage of prednisone to be reduced in MG patients. In a randomized clinical trial conducted by Wolfe and coworkers,20 thymectomy produced improvement in two endpoints after 3 years in patients with nonthymomatous MG: the Quantitative MG Score and a lower average prednisone dosage. Although thymectomy is not a necessary precursor to remission in MG patients, it is still pertinent in reducing the adverse effects of long-term steroid use – providing objective evidence to support thymectomy as a treatment option.
Emerging therapies
Although conventional treatments for MG are well-established, 10% to 20% of MG patients remain refractory to therapeutic intervention.21 These patients are more susceptible to myasthenic crisis, which can result in hospitalization, intubation, and death.21 As mentioned, rescue therapies, including plasmapheresis and IVIg, are imperative to achieve remission of refractory MG, but such remission is unsustainable. Risks associated with these therapies, including contraindications and patient comorbidity, and their limited availability have prevented plasmapheresis and IVIg from being reliable interventions.12
These shortcomings, along with promising results from randomized clinical trials of newer modes of pharmacotherapeutic intervention, have increased interest in new therapies for MG. For example, complement pathway and neonatal Fc receptor (FcRn) inhibitors have recently shown promise in removing pathogenic autoimmune antibodies.18
Efgartigimod. FcRn is of interest in treating generalized MG because of its capacity to recycle and extend the half-life of IgG.22 Efgartigimod is a high-affinity FcRn inhibitor that simultaneously reduces IgG recycling and increases its degradation.22 This therapy is unique: it is highly selective for IgG, whereas other FcRn therapies are nonspecific, causing an undesirable decrease in other immunoglobulin and albumin levels.22 In December 2021, the Food and Drug Administration approved efgartigimod for the treatment of AChR-positive generalized MG.23
Zilucoplan is a subcutaneously administered complement inhibitor that has completed phase 3 clinical trials.18,24 The drug works by inhibiting cleavage of proteins C5a and C5b in the terminal complement complex, a necessary step in forming cytotoxic pores on targeted cells.18,24 Zilucoplan also prevents tissue damage and destruction of signal transmission at the postsynaptic membrane.25 Clinical trials have already established improvement in the Quantitative MG Score and the Myasthenia Gravis Activities of Daily Living Score in patients with generalized MG.18,24
Zilucoplan is similar to eculizumab, but targets a different binding site, allowing for treatment of heterogeneous MG populations who have a mutation in the eculizumab target antigen.26 Additionally, due to specific drug-body interactions, parameters for treatment using zilucoplan are broader than for therapies such as eculizumab. In a Zilucoplan press-release, the complement inhibitor showed statistically significant improvement in the treatment group of generalized, AChR-positive MG patients compared to the placebo group. Tolerability and safety was also a favorable finding in this study. However, a similar rate of treatment-emergent adverse events were recorded between the treatment group (76.7%) and placebo group (70.5%) which could indicate that the clinical application of this treatment is still forthcoming.27 If zilucoplan is approved by the FDA, it will be used earlier in disease progression and for a larger subset of patients.26
Nipocalimab is another immunoglobulin G1, FcRn antibody that reduces IgG levels in blood.27,28 A phase 2 clinical study in patients with AChR-positive or MuSK antibody–associated MG showed that 52% of patients who received nipocalimab had a significant reduction in the Myasthenia Gravis Activities of Daily Living Score 4 weeks after infusion.28 Phase 3 studies for adults with generalized MG are underway and are expected to conclude in April 2026.29
Looking forward
Despite emerging therapies aimed at treating IgG in both refractory and nonrefractory MG, there is still a need for research into biomarkers that further differentiate disease. Developing research into new biomarkers, such as circulating microRNAs, gives insight into the promise of personalized medicine, which can shape the landscape of MG and other disorders.30 As of August 2022, only two clinical trials are slated for investigation into new biomarkers for MG.
Although the treatment of MG might have once been considered stagnant, newer expert consensus and novel research are generating optimism for innovative therapies in coming years.
Mr. van der Eb is a second-year candidate in the master’s of science in applied life sciences program, Keck Graduate Institute, Claremont, Calif.; he has an associate’s degree in natural sciences from Pasadena City College, Calif., and a bachelor’s degree in biological sciences from the University of California, Irvine. Ms. Toruno is a graduate from the master’s of science in applied life sciences program, Keck Graduate Institute; she has a bachelor’s degree in psychology, with a minor in biological sciences, from the University of California, Irvine. Dr. Laird is director of clinical education and professor of practice for the master’s of science in physician assistant studies program, Keck Graduate Institute; he practices clinically in general and thoracic surgery.
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2. Gilhus NE, Verschuuren JJ. Myasthenia gravis: Subgroup classification and therapeutic strategies. Lancet Neurol. 2015 Oct;14(10):1023-36. doi: 10.1016/S1474-4422(15)00145-3.
3. Dresser L et al. Myasthenia gravis: Epidemiology, pathophysiology and clinical manifestations. J Clin Med. 2021 May;10(11):2235. doi: 10.3390/jcm10112235.
4. Iyer SR et al. The neuromuscular junction: Roles in aging and neuromuscular disease. Int J Mol Sci. 2021 Jul;22(15):8058. doi: 10.3390/ijms22158058.
5. Hehir MK, Silvestri NJ. Generalized myasthenia gravis: Classification, clinical presentation, natural history, and epidemiology. Neurol Clin. 2018 May;36(2):253-60. doi: 10.1016/j.ncl.2018.01.002.
6. Prüss H. Autoantibodies in neurological disease. Nat Rev Immunol. 2021 Dec;21(12):798-813. doi: 10.1038/s41577-021-00543-w.
7. Drachman DB et al. Myasthenic antibodies cross-link acetylcholine receptors to accelerate degradation. N Engl J Med. 1978 May 18;298(20):1116-22. doi: 10.1056/NEJM197805182982004.
8. Meriggioli MN. Myasthenia gravis with anti-acetylcholine receptor antibodies. Front Neurol Neurosci. 2009;26:94-108. doi: 10.1159/000212371.
9. Zhang HL, Peng HB. Mechanism of acetylcholine receptor cluster formation induced by DC electric field. PLoS One. 2011;6(10):e26805. doi: 10.1371/journal.pone.0026805.
10. Fichtner ML et al. Autoimmune pathology in myasthenia gravis disease subtypes is governed by divergent mechanisms of immunopathology. Front Immunol. 2020 May 27;11:776. doi: 10.3389/fimmu.2020.00776.
11. Tzartos JS et al. LRP4 antibodies in serum and CSF from amyotrophic lateral sclerosis patients. Ann Clin Transl Neurol. 2014 Feb;1(2):80-87. doi: 10.1002/acn3.26.
12. Narayanaswami P et al. International consensus guidance for management of myasthenia gravis: 2020 update. Neurology. 2021;96(3):114-22. doi: 10.1212/WNL.0000000000011124.
13. Cortés-Vicente E et al. Myasthenia gravis treatment updates. Curr Treat Options Neurol. 2020 Jul 15;22(8):24. doi: 10.1007/s11940-020-00632-6.
14. Tannemaat MR, Verschuuren JJGM. Emerging therapies for autoimmune myasthenia gravis: Towards treatment without corticosteroids. Neuromuscul Disord. 2020 Feb;30(2):111-9. doi: 10.1016/j.nmd.2019.12.003.
15. Silvestri NJ, Wolfe GI. Treatment-refractory myasthenia gravis. J Clin Neuromuscul Dis. 2014 Jun;15(4):167-78. doi: 10.1097/CND.0000000000000034.
16. Sanders DB et al. International consensus guidance for management of myasthenia gravis: Executive summary. Neurology. 2016 Jul 26;87(4):419-25. doi: 10.1212/WNL.0000000000002790.
17. Evoli A, Meacci E. An update on thymectomy in myasthenia gravis. Expert Rev Neurother. 2019 Sep;19(9):823-33. doi: 10.1080/14737175.2019.1600404.
18. Habib AA et al. Update on immune-mediated therapies for myasthenia gravis. Muscle Nerve. 2020 Nov;62(5):579-92. doi: 10.1002/mus.26919.
19. O’Sullivan KE et al. A systematic review of robotic versus open and video assisted thoracoscopic surgery (VATS) approaches for thymectomy. Ann Cardiothorac Surg. 2019 Mar;8(2):174-93. doi: 10.21037/acs.2019.02.04.
20. Wolfe GI et al; MGTX Study Group. Randomized trial of thymectomy in myasthenia gravis. N Engl J Med. 2016;375(6):511-22. doi: 10.1056/NEJMoa1602489.
21. Schneider-Gold C et al. Understanding the burden of refractory myasthenia gravis. Ther Adv Neurol Disord. 2019 Mar 1;12:1756286419832242. doi: 10.1177/1756286419832242.
22. Howard JF Jr et al; . Safety, efficacy, and tolerability of efgartigimod in patients with generalised myasthenia gravis (ADAPT): A multicentre, randomised, placebo-controlled, phase 3 trial. Lancet Neurol. 2021 Jul;20(7):526-36. doi: 10.1016/S1474-4422(21)00159-9.
23. U.S. Food and Drug Administration. FDA approves new treatment for myasthenia gravis. News release. Dec 17, 2021. Accessed Feb 21, 2022. http://www.fda.gov/news-events/press-announcements/fda-approves-new-treatment-myasthenia-gravis.
24. Ra Pharmaceuticals. A phase 3, multicenter, randomized, double blind, placebo-controlled study to confirm the safety, tolerability, and efficacy of zilucoplan in subjects with generalized myasthenia gravis. ClinicalTrials.gov Identifier: NCT04115293. Updated Jan 28, 2022. Accessed Feb 21, 2022. https://clinicaltrials.gov/ct2/show/NCT04115293.
25. Howard JF Jr et al. Zilucoplan: An investigational complement C5 inhibitor for the treatment of acetylcholine receptor autoantibody–positive generalized myasthenia gravis. Expert Opin Investig Drugs. 2021 May;30(5):483-93. doi: 10.1080/13543784.2021.1897567.
26. Albazli K et al. Complement inhibitor therapy for myasthenia gravis. Front Immunol. 2020 Jun 3;11:917. doi: 10.3389/fimmu.2020.00917.
27. UCB announces positive Phase 3 results for rozanolixizumab in generalized myasthenia gravis. UCB press release. December 10. 2021. Accessed August 15, 2022. https://www.ucb.com/stories-media/Press-Releases/article/UCB-announces-positive-Phase-3-results-for-rozanolixizumab-in-generalized-myasthenia-gravis.
28. Keller CW et al. Fc-receptor targeted therapies for the treatment of myasthenia gravis. Int J Mol Sci. 2021 May;22(11):5755. doi: 10.3390/ijms22115755.
29. Janssen Research & Development LLC. Phase 3, multicenter, randomized, double-blind, placebo-controlled study to evaluate the efficacy, safety, pharmacokinetics, and pharmacodynamics of nipocalimab administered to adults with generalized myasthenia gravis. ClinicalTrials.gov Identifier: NCT04951622. Updated Feb 17, 2022. Accessed Feb 21, 2022. https://clinicaltrials.gov/ct2/show/NCT04951622.
30. Sabre L et al. Circulating miRNAs as potential biomarkers in myasthenia gravis: Tools for personalized medicine. Front Immunol. 2020 Mar 4;11:213. doi: 10.3389/fimmu.2020.00213.
