グルコースクランプ法でインスリン抵抗性の増大が確認された筋緊張性ジストロフィーの1例

Abstract

We report a case of myotonic dystrophy with diabetes mellitus. A 37-year -old man was admitted for further examination of liver dysfunction, diabetes mellitus, and myotonic dystrophy. His father, his mother and his sister had been previously diagnosed as having myotonic dystrophy. He had been mentally retarded since childhood, and suffered from muscle weakness and hardness of hearing. He was diagnosed as having bilateral cataracts at the age of 30, when loss of hair gradually started to be noticed. Physical examination revealed atrophy of bilateral sternocleidomastoid muscles and muscle weak- ness. Laboratory investigations showed hyperlipidemia, liver dysfunction, hyperglycemia and primary hypogonadism. ECG showed lst degree of AV block, EMG myotonic discharge dominantly in distal side. The microscopic findings of muscle biopsy showed hypertrophy of muscle fibers, predominantly in type 1 fibers. These findings were compatible with the diagnosis of myotonic dystrophy. DNA analysis of this patient showed an abnormal band of 6.2 Kb and 3.6 Kb (control; 3.4Kb). His glucose infusion rate by the glucose clamp technique was decreased to about 6.0 mg/kg/min (normal range : 8.9±1.1). We discuss the pathogenesis of insulin resistance in patients with myotonic dystrophy based on relevant studies published in the literature.