Histiocytosis X of the thymus in association with myasthenia gravis.

A patient with myasthenia gravis underwent thymectomy following the failure of medical treatment. The thymus was normal except for four nodules, which, on histologic and electron microscopic examination, were found to consist of proliferative clusters of Langerhans' cells characteristic of histiocytosis X. This patient therefore had two disease processes in which thymic abnormalities are frequently encountered, but their simultaneous occurrence in the same patient has not hitherto been documented. The case is briefly discussed in the context of current concepts of the pathogenesis of histiocytosis X and myasthenia gravis.