Myotonic dystrophy associated with insulinoma.

We describe a 51-year-old man with myotonic dystrophy (MyD) associated with insulinoma. In addition to the typical symptoms of MyD, he showed hypoglycemic attacks after meals. The radiological examination and selective blood sampling revealed an insulinoma in the head of the pancreas. The tumor was resected and histopathologically diagnosed as an insulinoma. In Southern blot analysis, CTG repeat of the myotonin protein kinase gene in the insulinoma showed the longest expansion, followed by normal tissue of the pancreas, muscle and white blood cells. Therefore, microsatellite instability was the most prominent in the tumor cells.