Myasthenia gravis: signs, symptoms, diagnosis, immunology, and current therapy.

Myasthenia gravis is a neuromuscular disease that presents clinically as fluctuating weakness of one or more skeletal muscle groups. Weakness becomes more severe with exercise and improves with rest. The disease is caused by an autoimmune reaction at or near the post-synaptic nicotinic acetylcholine receptor. The results of this immune reaction are the lytic destruction of the post-synaptic membrane and a reduction in the number of acetylcholine receptors. Myasthenia gravis can be diagnosed by repetitive exercise of the involved muscles, administration of edrophonium (Tensilon), electrophysiologic testing, or demonstration of anti-acetylcholine receptor antibodies. When the myasthenic weakness is mild or limited to the extraocular muscles, it may be treated with acetylcholinesterase inhibitors. When the weakness is more severe and/or more generalized, immunotherapy is most often indicated. Prednisone or prednisone plus thymectomy is the most frequently used form of immunotherapy. Azathioprine, 6-mercaptopurine, plasmapheresis, or gamma globulin injections are other immunotherapeutic options that may be useful in selected patients. A large number of drugs may precipitate or exacerbate myasthenic weakness.