Case report A pediatric patient with myopathy associated with antibodies to a signal recognition particle Takayoshi Kawabata a , Hirofumi Komaki a,⇑ , Takashi Saito a , Yoshiaki Saito a , Eiji Nakagawa a , Kenji Sugai a , Masayuki Sasaki a , Yukiko K. Hayashi b , Ichizo Nishino b , Mei Momomura c , Toshitaka Kizawa c , Tomoyuki Imagawa c , Shumpei Yokota c a Department of Child Neurology, National Center Hospital, National Center of Neurology and Psychiatry, Tokyo, Japan b National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan c Department of Pediatrics, Yokohama City University, Kanagawa, Japan Received 18 November 2011; received in revised form 22 February 2012; accepted 23 February 2012 Abstract We report the case of a 15-year-old Japanese girl with myopathy associated with antibodies to a signal recognition particle (anti- SRP myopathy). The patient presented with progressive symmetrical proximal muscle weakness that caused difficulty in walking within 3 months, and marked elevation of the serum creatine kinase levels. A skeletal muscle biopsy revealed active necrotic and regenerating processes, with mild inflammatory changes. Based on the above findings, the patient was diagnosed as having anti- SRP myopathy. Only a limited number of pediatric patients with anti-SRP myopathy has been reported previously, with usually a poor prognosis. Early diagnosis is important for obtaining a better prognosis in patients with anti-SRP myopathy. Ó 2012 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved. Keywords: Signal recognition particle; Anti-SRP myopathy; Muscular dystrophy; Inflammatory myopathy; Myositis; Muscle pathological findings 1. Introduction Antibodies to signal recognition particle (SRP) are known to be specific to myositis [1], and have been used recently to discriminate between myositis and muscular dystrophy. The SRP complex is ubiquitous cytoplasmic ribonuclear protein consisting of a small 7SL-RNA associated with six polypeptides with molecular weights of 9, 14, 19, 54, 68, and 72 kDa. The SRP transports proteins to the endoplasmic reticulum. Anti-SRP anti- bodies are detected in 5–6% of all middle-aged patients with idiopathic inflammatory myopathy, but in less than 1% of those with myopathy of childhood onset [1]. Adult patients with anti-SRP myopathy show symmetri- cal proximal muscle weakness, elevation of the serum creatine kinase (CK) levels in the range of 3064– 25,000 IU/l (median 8000) [2], and resistance to cortico- steroid therapy. Anti-SRP myopathy is also called nec- rotizing myopathy, since numerous necrotic fibers are seen on muscle pathology [3]. Lymphocyte infiltration is usually mild or localized to restricted areas, and perifascicular atrophy is not seen. From these clinical and pathological findings, it is sometimes difficult to dif- ferentiate between anti-SRP myopathy and muscular dystrophy [4]. Herein, we report the case of a 15-year-old patient with severe anti-SRP myopathy, who showed an early 0387-7604/$ - see front matter Ó 2012 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.braindev.2012.02.009 ⇑ Corresponding author. Address: Department of Child Neurology, National Center Hospital, National Center of Neurology and Psychi- atry, 4-1-1 Ogawa-Higashicho, Kodaira, Tokyo 187-8551, Japan. Tel.: +81 42 341 2711; fax: +81 42 344 6745. E-mail address: komakih@ncnp.go.jp (H. Komaki). www.elsevier.com/locate/braindev Brain & Development 34 (2012) 877–880