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.