[A case of myasthenia gravis appearing after thymomectomy: with histopathological investigation]

We report a 64-years old man who had myasthenia gravis (MG) appearing after surgical removal of thymoma. His thymoma was not removed completely due to adhesion with other organs. Histopathologicaly, the thymoma was an invasive and predominantly epithelial type. CD45RO positive cells increased in the thymus. After five months of thymectomy, he received radiation therapy because the remaining tumor grew up slightly. The radiation was effective, and the recurrence of tumor has never been detected after that. However, nine months after the surgery, he noticed ptosis and double vision, and he was diagnosed as MG because of positive serum anti-AchR antibody and positive Tensilon test. He received oral prednisolone, and he has kept a good condition. Previous reports have shown that an extensive thymectomy tends to reduce the incidence of post-operative MG. In our case, the remaining thymoma might increase the risk of MG. And the removed thymus might contain an unknown regulatory factor that could inhibit a development of MG. The risk factor for development of post-operative MG should be investigated in future.