The pathology of the thymus in myasthenia gravis

Myasthenia gravis (MG) is an autoantibody mediated autoimmune disease characterized by skeletal muscle fatigability and weakness through different types of immune attacks against various proteins of the postsynaptic membrane or in the neuromuscular cleft of the neuromuscular junction. In a subset of patients with autoantibodies against the muscle type acetylcholine receptors (AChRs) there is strong evidence that the thymus is involved in the pathogenesis of MG, while its role is questionable or unknown in MG due to autoantibodies against muscle specific kinase (MuSK), lipoprotein receptor like protein 4 and agrin. Here we describe the thymic alterations that have repeatedly been encountered in MG, i.e., thymic follicular hyperplasia (TFH) (thymitis), ‘thymic atrophy’, thymoma and thymolipoma. The potential link of non-thymic tumors [e.g., follicular dendritic cell (FDC) sarcoma] with MG will be discussed.