Myasthenia gravis is a rare, chronic disorder that causes weakness and rapid fatigue of muscles. The muscle weakness develops slowly, first affecting the facial muscles and causing symptoms that include drooping eyelids, double vision, and difficulty talking, chewing, swallowing, or breathing.

The exact cause of myasthenia gravis is not known, but it is known that the antibodies formed by the body's immune system to fight infection instead attack normal muscle tissue. Myasthenia gravis can occur at any age in both women and men, but it is most common in young women who have problems with the thymus gland.

Treatment for myasthenia gravis includes medication to help reduce and improve muscle weakness. Surgery to remove the thymus gland may be helpful in some cases.