胸腔鏡下肺生検にて通常型間質性肺炎診断4年後に皮膚筋炎と診断された1例

A Case of Dermatomyositis Occurring 4 Years after the Histologic Diagnosis of Usual Interstitial Pneumonia by VATS

要旨　患者は70歳，女性で，通常型間質性肺炎（UIP）診断4年後に皮膚筋炎を発症した症例である．1992年8月胸部X線写真上異常を指摘された．1995年3月陰影が増悪し，胸部CT上は両下肺野で容量減少が著明で斑状，網状陰影を指摘され，胸腔鏡下肺生検でUIPと診断された．以後経過観察されていたが，1999年3月より微熱，四肢近位筋の筋力低下，皮疹，筋原性酵素の上昇が出現し，筋生検にて皮膚筋炎と診断された．ステロイド薬・免疫抑制薬にて筋原性酵素は正常化したが，間質性肺炎の変化はなかった．多発筋炎，皮膚筋炎は比較的高率に間質性肺炎を合併する．また，間質性肺炎が先行する多発筋炎，皮膚筋炎も決して少なくない．しかし，本症例のようにUIPと診断された4年後に皮膚筋炎を発症する例は稀である．原因不明の間質性肺炎を経過観察するときは，膠原病の発症も念頭におく必要がある。

　A 70-year-old woman with interstitial pneumonia complicated by dermatomyositis 4 years after the diagnosis of interstitial pneumonia was reported. She wasadmitted to the respiratory department of our hospital on March 29, 1995 because of newly aggravated abnormal lung shadow, which had been first pointed out in August, 1992. Chest roentogenograms and CT showed patchy reticular shadows mainly in both lower lung fields with a marked loss of volume of the fields. She was followed-up, in the out-clinic, after a diagnosis of usual interstitial pneumonia, through transbronchial lung biopsy and video-assisted thoracoscopic surgery. This follow-up was carried ont until March, 1999, when she noted low fever, weakness of proximal muscles and skin eruptions. Elevated serum muscle enzymes and histologic findings in addition to clinical features were compatible with those of dermatomyositis. Although the myositis was well controlled with steroid and immunosuppressive therapies, her lung shadow did not change. Polymyositis and dermatomyositis are sometimes associated with interstitial pneumonia, and cases of interstitial pneumonia precedent to polymyositis or dermatomyositis are not rare. However, a case of dermatomyositis occurring long after the start of interstitial pneumonia as in the present case is rare. When interstitial pneumonia is diagnosed, its complication by collagen disease should be searched for carefully throughout the clinical course.