Thymus, thymoma and myasthenia gravis.

Myasthenia gravis is an autoimmune disease. An autoantibody directed toward acetylcholine receptor (AChR) causes the destruction of the postsynaptic membrane and a reduction of the number of AChRs at neuromuscular junctions. A very puzzling, but interesting characteristic of myasthenia gravis is that many of the patients have an abnormality in their thymus. Many have a hyperplastic thymus with germinal centers, while others have a thymic tumor. How is the abnormality of the thymus related to myasthenia gravis? This review will summarize the existing evidence and try to find the missing link between the thymus and myasthenia gravis. The review will also comment on two distinct populations of myasthenia gravis patients without thymoma. The autoimmunity found in elderly patients is nonspecific and initiated via a different mechanism from the initiation of myasthenia gravis in younger patients.