[A case of myasthenia gravis accompanied by large thymoma and anti-GAD antibody]

A 61-year-old woman had repeated episodes of muscle weakness of face, neck and limbs for 18 years. She was diagnosed as having myasthenia gravis (MG) by the positive anti-acetylcholine receptor antibody and findings of electromyogram. Simultaneously, she was noticed to have diabetes mellitus with high titers of anti-glutamic acid decarboxylase (GAD) antibody. Magnetic resonance imaging showed a large thymoma. In spite of the improvement of MG after thymectomy, the insulin secretion slowly exacerbated during next two years. The clinical course of her disease was characteristic as slowly progressive insulin dependent diabetes mellitus (SPIDDM). She continued to have positive autoantibody against beta-cell of pancreas. Recently, anti-GAD antibody is detected in patients with SPIDDM and stiffman syndrome (SS) in high rate, and it is closely associated with the cause of these syndromes. The patient did not reveal the symptoms of SS. From the clinical course, MG and SPIDDM in this patient may be caused by a common underlying autoimmune abnormality resulting from the long presence of the thymoma. MG and SPIDDM may be derived from organ-specific autoimmunopathy from the defect of self-tolerance.