Effective induction therapy for anti-SRP associated myositis in childhood: A small case series and review of the literature

E. L. Binns, E. Moraitis, S. Maillard, S. Tansley, N. McHugh, T. S. Jacques, L. R. Wedderburn, C. Pilkington, S. A. Yasin, K. Nistala, on behalf of the UK Juvenile Dermatomyositis Research Group (UK and Ireland)

Anti-Signal Recognition Particle associated myopathy is a clinically and histopathologically distinct subgroup of Juvenile Idiopathic Inflammatory Myositis, which is under-recognised in children and fails to respond to conventional first line therapies. We present three cases where remission was successfully induced using combination therapy with intensive rehabilitation. Three new patients are reported. All 3 cases presented with profound, rapid-onset, proximal myopathy and markedly raised CK, but no rash. Histology revealed a destructive myopathy characterized by scattered atrophic and necrotic fibres with little or no inflammatory infiltrate. All 3 patients responded to induction with cyclophosphamide, IVIG and rituximab, in conjunction with intensive physiotherapy and methotrexate as the maintenance agent. Our patients regained near-normal strength (MMT > 70/80), in contrast with the current literature where >50% of cases reported severe residual weakness. A literature search on paediatric anti-SRP myositis was performed to June 2016; PubMed was screened using a combination of the following terms: signal recognition particle, autoantibodies, antibodies, myositis, muscular diseases, skeletal muscle, childhood, paediatric, juvenile. Articles in a foreign language were excluded. Nine case studies were found. This paper supports the hypothesis that anti-SRP myositis is distinct from other JIIM. It is an important differential to JDM and should be considered where there is severe weakness without rash or if highly elevated muscle enzymes (CK > 10,000 U/l) are found. Early identification is essential to initiate aggressive medical and physical therapy. Greater international collaboration and long-term follow-up data is needed to establish the most effective treatment strategy for this rare group of patients.