Immunoperoxidase staining for leu14 antigen identifies thymic B lymphocyte follicular hyperplasia in myasthenia gravis

Myasthenia gravis associated with follicular hyperplasia has a high chance of clinical improvement or even complete remission when thymectomy is performed. However, there are rare cases in which the thymus appears normal on routine histologic examination because the lymph follicles are not transformed to secondary follicles with germinal centers. An immunoperoxidase method that probes for an early appearing B cell surface antigen, Leul4, is an excellent tool for the demonstration of inapparent (cryptic) B cell hyperplasia, thus leading to the correct diagnosis. This is a report of such a case of a patient with atypical myasthenia gravis who had a slightly enlarged but mostly non-follicular thymus on pathologic examination. The diagnosis of B lymphocyte hyperplasia required immunocytochemical methods. Thymectomy led to almost complete clinical remission.