Myasthenia gravis (MG) is the most common neuromuscular junction disease and presents with weakness worsened by exertion but improving with rest.
Incidence is estimated at 15-20 per 100,000 1,2. Females are more affected (3:1) under the age of 40, but males are more affected by the age of 50 2.
The classic feature of myasthenia gravis is fluctuating weakness that is fatiguable, worsening with activity and improving with rest 2. Two-thirds of patients present with ocular symptoms (e.g. diplopia, ptosis), with the majority (80%) proceeding to experience generalized weakness 1.
Myasthenia gravis is an autoimmune disease. The disease can be associated with several antibodies. These include:
- anti-AChR: antibodies affecting postsynaptic acetylcholine receptors
- anti-MuSK: antibodies affecting muscle specific kinase
- titin ab
- RyR ab
thymic lymphoid hyperplasia
- may be seen in around 65% of cases with myasthenia gravis 8
- ~40% of patients with thymoma have myasthenia gravis
- 10-15% of patients with myasthenia gravis have a thymoma
- other autoimmune diseases, e.g. thyroiditis, rheumatoid arthritis, systemic lupus erythematosus 5
- myocarditis 5
Treatment and prognosis
Symptomatic treatment with cholinesterase inhibitors are first line treatment in myasthenia gravis. Plasmapharesis and immunoglobulin therapy are sometimes used in the acute setting also. Corticosteroids and immunosuppressive drugs (e.g. cyclosporin, cyclophosphamide, azathioprine and mycophenolate mofetil) are used for immunomodulation in the chronic setting of the disease 2,6. Thymectomy for patients with a thymoma is usually recommended 2.
Patients with myasthenia gravis can present with a sudden worsening of symptoms termed a myasthenic crisis which can compromise the respiratory muscles in some cases. This can be precipitated by concurrent infection or medication use (e.g. aminoglycosides) 2.
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- 4. Higuchi T, Taki J, Kinuya S et-al. Thymic lesions in patients with myasthenia gravis: characterization with thallium 201 scintigraphy. Radiology. 2001;221 (1): 201-6. doi:10.1148/radiol.2211001047 - Pubmed citation
- 5. Sieb JP. Myasthenia gravis: an update for the clinician. Clin. Exp. Immunol. 2014;175 (3): 408-18. doi:10.1111/cei.12217 - Free text at pubmed - Pubmed citation
- 6. Heatwole C, Ciafaloni E. Mycophenolate mofetil for myasthenia gravis: a clear and present controversy. Neuropsychiatr Dis Treat. 2011;4 (6): 1203-9. Free text at pubmed - Pubmed citation
- 7. Hart IK, Sharshar T, Sathasivam S. Immunosuppressant drugs for myasthenia gravis. J. Neurol. Neurosurg. Psychiatr. 2008;80 (1): 5-6. doi:10.1136/jnnp.2008.144980 - Pubmed citation
- 8. Priola AM, Priola SM. Imaging of thymus in myasthenia gravis: from thymic hyperplasia to thymic tumor. Clinical radiology. 69 (5): e230-45. doi:10.1016/j.crad.2014.01.005 - Pubmed