- Eye movement abnormalities cause a range of symptoms from visual blurriness to frank diplopia. Ocular symptoms including asymmetric ptosis are common and among the presenting symptoms in over half of patients.
- In generalized MG, dysphagia, dysarthria, fatigable chewing, hypophonia, neck muscle weakness, and proximal limb weakness may be prominent in addition to ocular manifestations. Diaphragm paralysis may occur in advanced stages, leading to crisis and the need for respiratory assistance.
Autoimmune MG is thought to involve antibodies to the acetylcholine receptor (AChR-Ab), and such antibodies are detectable in approximately 80%-85% of patients. About 40% of patients who do not have AChR-Ab will have antibodies to muscle-specific tyrosine kinase (MuSK-Ab), a receptor-associated protein. About 10% of acquired cases remain seronegative; this is more common among patients with isolated ocular myasthenia. There are also congenital and juvenile forms of the disease.
In generalized MG, females are affected more frequently than males (3:2). It is somewhat more common in women under 40 and men over 60. MG is associated with other autoimmune disorders, including thymoma, thyroid disease, Hashimoto thyroiditis, scleroderma, rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis. Additionally, in patients with MG who become pregnant, the highest risk for exacerbation occurs in the first trimester and in the acute postpartum period.
There is no cure, but MG can be managed with anti-acetylcholinesterase medications, thymectomy, and immunosuppression. Most patients have an average life span, although exacerbations of the disease can lead to intubation and even death.
For more information, see OMIM.
G70.00 – Myasthenia gravis without (acute) exacerbation
G70.01 – Myasthenia gravis with (acute) exacerbation
91637004 – Myasthenia gravis
- Inherited congenital myasthenic syndromes – While autoimmune MG is the predominant form, genetic mutations affecting the neuromuscular junction may be present. This diagnosis requires molecular analysis and likely genetic counseling.
- Lambert-Eaton myasthenic syndrome (LEMS) – Proximal muscles are often affected first, and ptosis and diplopia are common. Unlike muscle changes in MG, weakness is often improved with exertion in LEMS (Lambert's sign). Also, patients may develop autonomic symptoms, reflexes are diminished, and squamous cell lung cancer is common in LEMS. Similar to MG, respiratory distress is common in advanced disease. Immunosuppression and plasmapheresis are often necessary in severe disease.
- Thyroid ophthalmopathy
- Kearns-Sayre syndrome
- Myotonic dystrophy
- Intracranial mass causing brainstem or cranial nerve pathology
- Drug-induced MG – Common offending agents include penicillamine, aminoglycosides, quinolones, macrolides, and procainamide.
- Hyperthyroidism (Graves disease)
- Oculopharyngeal dystrophy
- Depression / apathy
- Generalized fatigue