Extramedullary plasmacytoma presenting with myasthenia gravis and mediastinal mass.

A 68-year-old woman presented with myasthenia gravis and an anterior mediastinal mass, which proved to be an extramedullary plasmacytoma in the thymus with associated extracellular light chain deposition. Further specimens revealed plasma cell proliferation in an internal thoracic lymph node and in a subsequent colectomy specimen, indicating systemic disease. This case demonstrates the rare association between a plasmacytoma in the thymus and myasthenia gravis.