Hyun Ho Kim,1 Jae Young Kim,1 Sung Jun Kim,1,2 Eun Su Park,3 Seok Joon Shin,1,2 Kwi Young Kang,1,4 Yeon Sik Hong,1,4 Hye Eun Yoon1,21Department of Internal Medicine, College of Medicine, The Catholic University of Korea, 2Division of Nephrology, Department of Internal Medicine, Incheon St Mary's Hospital, 3Department of Pathology, Incheon St Mary's Hospital, 4Division of Rheumatology, Department of Internal Medicine, Incheon St Mary's Hospital, Incheon, Republic of KoreaAbstract: Polymyositis

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... a rare and gradually progressive autoimmune disease of skeletal muscle. Two main types of renal involvement have been described: acute tubular necrosis related to rhabdomyolysis and glomerulonephritis. However, cases of overflow proteinuria related to polymyositis have rarely been reported. Herein, we report a case of a 41-year-old male who presented with edema of both lower extremities. Laboratory studies revealed elevated creatine phosphokinase level, hypoalbuminemia, and a moderate amount of proteinuria, although albuminuria was not dominant. Urine electrophoresis showed an abnormally restricted zone in the β-fraction, which suggested overflow proteinuria of non-glomerular origin. Despite intravenous hydration, his serum creatine phosphokinase level did not decrease and his symptoms did not improve. Electromyography showed myopathy, and muscle biopsy revealed findings consistent with polymyositis. After corticosteroid therapy, his creatine phosphokinase level and proteinuria decreased and his clinical symptoms improved. This case demonstrates an atypical presentation of polymyositis manifested by overflow proteinuria.Keywords: polymyositis, proteinuria, rhabdomyolysis