Myasthenia Gravis

Myasthenia gravis is a chronic autoimmune neuromuscular disease characterized by varying degrees of weakness of the skeletal (voluntary) muscles of the body. Myasthenia gravis literally means "grave muscle weakness." 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 control breathing and neck and limb movements may also be affected.

Signs and Symptoms

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.

Causes

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.

Diagnosis

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.

Exams and Tests

Several tests may be conducted to make a diagnosis of myasthenia gravis:

• Neurologic Exam. Myasthenia gravis has a hallmark sign which is muscle weakness that improves with rest. As a result, it is important to take a thorough history and do a complete neurological exam. The neurologist may test reflexes, muscle strength and tone, senses of touch and sight, gait, posture, coordination, balance and mental skills.

• Edrophonium Test. A chemical called (edrophonium) is injected into the bloodstream. A person with myasthenia gravis will experience a temporary improvement in their muscle strength when this chemical is administered.

• Nerve Conduction Studies and Single-Fiber Electromyography(EMG). These tests can measure the strength of muscle contraction. The nerves are stimulated by applying a electrical impulse to the skin. The impulses are repeated in order to determine if muscle weakness develops. A thin needle is then inserted into a muscle in order to measure the electrical activity in the muscle.

• Blood Tests. Blood tests can be done that will look for antibodies that are found in people with myasthenia gravis.

Treatment

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 (which often is abnormal in myasthenia gravis patients), improves symptoms in certain patients and may cure some individuals, possibly by re-balancing the immune system. 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.

Chances of Developing Myasthenia gravis

Myasthenia gravis is not directly inherited nor is it contagious.

Prognosis

With treatment, the outlook for most patients with myasthenia is bright: they can expect to lead normal or nearly normal lives. Some cases 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.

Research

Scientists are evaluating new and improving current treatments for myasthenia gravis. One study is testing the efficacy of intravenous immune globulin, and another study seeks to understand the molecular basis of synaptic transmission in the nervous system.

Clinical Trials

• Hematopoietic Stem Cell Therapy for Patients With Refractory Myasthenia Gravis
• Thymectomy Trial in Non-Thymomatous Myasthenia Gravis Patients Receiving Prednisone Therapy
• Efficacy and Safety Study of GB-0998 for Treatment of Generalized Myasthenia Gravis

Other Resources

• Myasthenia Gravis Foundation of America, Inc.