Myasthenia gravis

[Dorothey Allen]

Myasthenia gravis involves episodic muscle weakness and easy fatigability caused by autoantibody- and cell-mediated destruction of acetylcholine receptors. It is more common among young women and older men but may occur in men or women at any age. Symptoms worsen with muscle activity and lessen with rest. Diagnosis is by measurement of serum acetylcholine receptor (AChR) antibody levels, electromyography, and sometimes IV edrophonium challenge, which briefly lessens the weakness. Treatment includes anticholinesterase drugs, immunosuppressants, corticosteroids, plasma exchange, IV immune globulin , and possibly thymectomy.
(See also Overview of Peripheral Nervous System Disorders.)
Myasthenia gravis develops most commonly in women aged 20 to 40 and men aged 50 to 80, but it can occur at any age, including childhood.
Myasthenia gravis results from an autoimmune attack on postsynaptic acetylcholine receptors, which disrupts neuromuscular transmission. The trigger for autoantibody production is unknown, but the disorder is associated with abnormalities of the thymus, autoimmune hyperthyroidism, and other autoimmune disorders (eg, rheumatoid arthritis [RA], systemic lupus erythematosus [SLE], pernicious anemia).
The role of the thymus in myasthenia is unclear, but 65% of patients have thymic hyperplasia, and 10% have a thymoma. About half of the thymomas are malignant.
Precipitating factors for myasthenia gravis include

Infection
Surgery
Certain drugs (eg, aminoglycosides, quinine , magnesium sulfate , procainamide , calcium channel blockers, immune checkpoint inhibitors)