[Painful unilateral gynecomastia in a patient with myotonic dystrophy].

A 54-year-old patient with myotonic dystrophy presented unilateral painful gynecomastia, which occurred 3 months after aggravation of diabetes mellitus. Serum luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels were slightly high. LH was elevated than 2 years before. Breast pain and gynecomastia disappeared by daily administration of 10 mg tamoxifen. He could not have intramuscular injection therapy because of marked muscle atrophy. Painful gynecomastia may be one of the endocrine complications in myotonic dystrophy.