Myasthenia gravis is a chronic autoimmune neuromuscular disease characterized by varying degrees of weakness of the skeletal (voluntary) muscles of the body. The hallmark of myasthenia gravis is muscle weakness that increases during periods of activity and improves after periods of rest.
Muscles that control eye and eyelid movements, facial expression, chewing, talking, and swallowing are often, but not always, involved. The muscles that that control breathing and neck and limb movements may also be affected.
Myasthenia gravis is caused by a defect in the transmission of nerve impulses to muscles. Normally when impulses travel down the nerve, the nerve endings release a neurotransmitter substance called acetylcholine. In myasthenia gravis, antibodies produced by the body's own immune system block, alter, or destroy the receptors for acetylcholine.
The first noticeable symptoms of myasthenia gravis may be weakness of the eye muscles, difficulty in swallowing, or slurred speech. Symptoms vary in type and severity. Myasthenia gravis is not directly inherited nor is it contagious.
The first steps in diagnosing myasthenia gravis include a review of the individual's medical history and physical and neurological examinations. If the doctor suspects myasthenia gravis, several diagnostic tests are available to confirm the diagnosis, including a special blood test that can detect the presence of immune molecules or acetylcholine receptor antibodies.
With treatment, the outlook for most patients with myasthenia is bright: they can expect to lead normal or nearly normal lives. Some case of myasthenia gravis may go into remission temporarily, and muscle weakness may disappear so that medications can be discontinued. In a few cases, the severe weakness of myasthenia gravis may cause respiratory failure, which requires immediate emergency medical care.
Myasthenia gravis can be controlled. Some medications improve neuromuscular transmission and increase muscle strength, and some suppress the production of abnormal antibodies. These medications must be used with careful medical followup because they may cause major side effects.
Thymectomy, the surgical removal of the thymus gland, improves symptoms in certain patients and may cure some individuals. Other therapies include plasmapheresis, a procedure in which abnormal antibodies are removed from the blood, and high-dose intravenous immune globulin, which temporarily modifies the immune system and provides the body with normal antibodies from donated blood.
Reviewed by Dr Andrew Rose-Innes, MD, Department of Neurology, Yale University School of Medicine, New Haven.