Myasthenia Gravis Basics

Myasthenia gravis is an autoimmune disorder of the postsynaptic neuromuscular junction. The motor nerve releases acetylcholine normally, but IgG autoantibodies interfere with the receiving side of the connection. Most patients have antibodies against the acetylcholine receptor (AChR). These antibodies may block the receptor, promote its removal from the membrane, or damage the receptor-containing membrane. Other patients have antibodies against MuSK or LRP4, proteins that help organize and maintain acetylcholine receptors at the motor endplate. The result is an unreliable endplate signal. A single nerve impulse may produce enough contraction at first, but repeated use places greater demand on a limited number of functioning receptors. Muscle strength then fades. Rest reduces the immediate demand on transmission, so strength temporarily returns; rest does not remove the autoantibodies or cure the disease. Because the primary problem is at the motor neuromuscular junction, sensation, pupils, and deep tendon reflexes are characteristically preserved. New sensory loss, abnormal pupils, or a clearly depressed level of consciousness should prompt consideration of another or additional neurologic process.