Myasthenia gravis (MG) is a chronic autoimmune disorder that results in progressive skeletal muscle weakness.
Skeletal muscles are primarily muscle fibers that contain bands or striations (striated muscles) that are connected to bone. MG causes rapid fatigue (fatigability) and loss of strength upon exertion that improves after rest.
In early stages, myasthenia gravis primarily affects muscles that control eye movement (extraocular muscles) and those that control facial expression, chewing, and swallowing. If untreated, the disorder may affect muscles that control breathing (respiration), causing acute respiratory failure.