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Research paper
Clinical features and prognosis in anti-SRP and anti-HMGCR necrotising myopathy
  1. Yurika Watanabe1,
  2. Akinori Uruha2,3,
  3. Shigeaki Suzuki1,
  4. Jin Nakahara1,
  5. Kohei Hamanaka2,4,
  6. Kazuko Takayama2,
  7. Norihiro Suzuki1,
  8. Ichizo Nishino2
  1. 1Department of Neurology, Keio University School of Medicine, Tokyo, Japan
  2. 2Department of Neuromuscular Research, National Institute of Neuroscience, Tokyo, Japan
  3. 3Department of Genome Medicine Development, Medical Genome Center, National Center of Neurology and Psychiatry, Tokyo, Japan
  4. 4Department of Neurology, Graduate School of Medicine, Kyoto University, Kyoto, Japan
  1. Correspondence to Dr Shigeaki Suzuki, Department of Neurology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan; sgsuzuki{at}z3.keio.jp

Abstract

Objective To elucidate the common and distinct clinical features of immune-mediated necrotising myopathy (IMNM), also known as necrotising autoimmune myopathy associated with autoantibodies against signal recognition particle (SRP) and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR).

Methods We examined a cohort of 460 patients with idiopathic inflammatory myopathies (IIMs) through a muscle biopsy-oriented registration study in Japan. Study entry was strictly determined by the comprehensive histological assessment to exclude other neuromuscular disorders. Anti-SRP and anti-HMGCR antibodies were detected by RNA immunoprecipitation and ELISA, respectively.

Results Of 460 patients with IIM, we diagnosed 73 (16%) as having inclusion body myositis (IBM). Of 387 patients with IIMs other than IBM, the frequencies of anti-SRP and anti-HMGCR antibodies were 18% and 12%, respectively. One patient had both autoantibodies. Severe limb muscle weakness, neck weakness, dysphagia, respiratory insufficiency and muscle atrophy were more frequently observed in patients with anti-SRP antibodies than in those with anti-HMGCR antibodies. Serum creatine levels were markedly higher in the patients with autoantibodies than in those without. Histology was characterised by necrosis and regeneration of muscle fibres and was consistent with IMNM except in 1 HMGCR-positive IBM patient. Most patients were initially treated with corticosteroids; however, additional immunosuppressive drugs were required, especially in the patients with anti-SRP antibodies. Rates of unsatisfactory neurological outcome were similar in the 2 autoantibody groups.

Conclusions Anti-SRP antibodies are associated with severe neurological symptoms, more so than are anti-HMGCR antibodies. Although these autoantibodies are independent serological markers associated with IMNM, patients bearing either share common characteristics.

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