Myasthenia Gravis (MG) is an autoimmune neuromuscular disease that results from a lack of communication between nerves and muscles. MG occurs in all races, both sexes and at any age. It is most common in young adult women and older men. It is not directly inherited nor is it contagious. MG does occasionally occur in more than one member of the same family. It may affect any muscle that is under voluntary control.
Certain muscles are more involved and these include the ones that control eye movements, eyelids, chewing, swallowing, coughing and facial expression. Muscles that control breathing and movements of the arms and legs may also be affected. Weakness of the muscles needed for breathing may cause shortness of breath.

The muscle weakness of MG increases with continued activity and improves after periods of rest. The muscles affected by MG vary greatly from one patient to the next. Weakness may be limited to the muscles controlling eye movement and the eyelids. This is the mildest form of the illness and is called ocular MG. In the severest form, MG involves many of the voluntary muscles of the body including those needed for breathing.