非アルコール性脂肪性肝炎の経過中に筋強直性ジストロフィーと診断された1例

症例は42歳女性で,弟に筋強直性ジストロフィーがある.脂肪肝と診断され,外来通院していたが,肝生検を施行され非アルコール性脂肪性肝炎(non-alcoholic steatohepatitis: NASH)と診断された.一方,今回入院の数年前より歩行が遅く,神経内科外来に紹介され精査目的で入院した.斧状顔貌を認めたが,grip myotoniaやpercussion myotoniaは明らかではなかった.四肢の筋力は正常だが, 歩行はやや緩徐であった.血液検査では総コレステロール,γGTP及びHOMA-IRの高値を認めた.針筋電図では,刺入時に急降下爆撃音が聴取された.遺伝子検査にてDMプロテインキナーゼ遺伝子のCTG反復配列が約1,300回と増幅を認めた.筋強直性ジストロフィーの家族歴,針筋電図検査,遺伝子検査から筋強直性ジストロフィー1型と確定診断した.筋強直性ジストロフィーは骨格筋の障害の他に,様々な臓器の障害をきたすことが知られているが,NASHを合併した報告例はごく少数である.近年NASHあるいは非アルコール性脂肪性肝疾患(non-alcoholic fatty liver disease: NAFLD)患者は急増しており,それらの中に筋強直性ジストロフィーが合併している場合があることも念頭に置くべきと考える.We report the case of a 42-year-old woman diagnosed with myotonic dystrophy during the clinical course of non-alcoholic steatohepatitis (NASH). She had been diagnosed fatty liver at age 33. When she was 40 years old, histopathological findings of a liver biopsy specimen indicated NASH. After that, she complained of gait disturbance. Brain CT and MRI revealed skull thickening, calcification of falx cerebri and atrophy of the lateral pterygoid muscles. She had a hatchet face. Her muscle strength was normal; she did not have grip myotonia nor percussion myotonia. On laboratory data, total cholesterol was 254 mg/dl, γGTP was 118 U/l, CK was 148 U/l, fasting plasma glucose was 103 mg/dl, fasting plasma insulin was 15.6 μU/ml, homeostasis model assessment-insulin resistance (HOMA-IR) was 3.967. A dive-bomber sound was heard on needle EMG. DM protein kinase gene analysis showed increase of CTG repeat. Occurrence of myotonic dystrophy during the clinical course of NASH is rare. NASH/non-alcoholic fatty liver disease (NAFLD) is strongly associated with insulin resistance. Insulin resistance in patients with myotonic dystrophy is highly prevalent and is due to a splicing abnormality of the insulin receptor in muscle tissue. In our patient, HOMA-IR was elevated and suggested an increase of insulin resistance. Thus, the risk of developing myotonic dystrophy should be considered in patients with NASH/NAFLD