Myasthenia gravis, << `my` uhs THEE nee uh GRAV ihs, >> is a noncontagious disease characterized by progressive weakness of the skeletal muscles. This weakness increases with physical activity but can be partially relieved by rest. The disease afflicts all age groups and both sexes but occurs most frequently among women from 15 to 30 years old and men 40 to 70 years old.
Myasthenia gravis affects primarily the skeletal muscles of the face, neck, arms, and legs (see Muscle ). Symptoms may include a drooping eyelid; difficulty in chewing, swallowing, and talking; fatigue; and general muscle weakness. Diagnosis can be difficult because the early symptoms are slight and may come and go.
Most researchers believe myasthenia gravis results from a defect at a neuromuscular junction, the point where a nerve impulse is transmitted to a muscle. Normally, a substance called acetylcholine is released from the nerve ending. Acetylcholine becomes attached to acetylcholine receptor molecules on the muscle surface, causing the muscle to contract. In myasthenia gravis, something causes the acetylcholine receptor molecules to become blocked or to decrease in number.
Researchers suspect that myasthenia gravis is an autoimmune disease. In such diseases, the body’s immune system, which normally attacks harmful bacteria and viruses, attacks the body’s own tissues. The immune system of myasthenia gravis patients appears to attack acetylcholine receptor molecules.
With medication, most patients with myasthenia gravis can live almost completely normal lives. Doctors usually treat symptoms of the disease with drugs, either anticholinesterases or immunosuppressives. Removal of the thymus gland, a part of the immune system, may be helpful, particularly during the early stages of the illness. In certain advanced cases, a procedure called plasmapheresis may be used. In this procedure, the physician withdraws the patient’s blood and filters out the immune substances that may be attacking the muscle receptors. The purified blood is then returned to the patient.
