Scientists are investigating what triggers the body to develop an autoimmune response. In many people, the thymus gland appears to be involved. The cells of the thymus gland form a part of the body's normal immune system. Located in the chest, the thymus is normally large in infancy, and shrinks in size so that in the normal adult it is hardly functional. In the myasthenic adult, however, the thymus gland is often abnormally enlarged.
Most myasthenic people have thymic abnormalities.
Ten to fifteen percent have tumours, called thymomas, which are usually relatively benign, but may become malignant. Although the relation of the thymus gland to MG is not fully understood, it is clear that the thymus is linked to the production of acetylcholine receptor antibodies that interfere with neuromuscular transmission. The use of drugs and surgery, alone or in combination, has been quite successful in the treatment of MG, allowing many patients to lead near normal lives. The first line of treatment is usually with drugs - called anticholinesterase agents that enhance neuromuscular transmission. While these drugs don't repair the basic deficiency in the acetylcholine receptors, they do prolong the effect of the acetylcholine that signals the muscles to act.