G.P.74: Anti-Signal Recognition Particle associated myopathy in a multiethnic Malaysian population

Abstract

Anti-Signal Recognition Particle (SRP) myopathy is a complement dependent antibody-mediated necrotising myopathy which is often clinically more severe and require longer and more aggressive immunosuppressive treatment. We describe a series of Malaysian patients with anti-SRP myopathy. Of 30 patients with idiopathic inflammatory myopathy, seen prospectively at the University of Malaya Medical Centre, Kuala Lumpur between 2012 and 2014, eight (26.7%) had positive anti-SRP antibodies. All patients were female, of whom four were ethnic Malays and four, ethnic Chinese. Their mean age of disease onset was 37years (range 24–60years). All presented with progressive severe proximal muscle weakness. Mean serum creatine kinase at presentation was 4994u/L (range 385–14,000iu/L). Muscle histopathology showed muscle fibre necrosis with variable regenerative features. Inflammation ranged from minimal to severe infiltration of lymphocytes in seven patients and in one patient, there was marked variation of fibre size with interstitial fibrosis, morphological features similar to that of muscular dystrophy. All patients responded only partially to corticosteroids and other immunosuppressive agents including methotrexate, mycophenolate mofetil, azathioprine and IVIG. Rituximab was given to one patient but with minimal improvement. Other associated autoantibodies found included anti Ro-52 in 50% and anti PM-Scl75 and anti PL-12 in 25% respectively. None had associated interstitial lung disease nor underlying malignancy. In prospective series inflammatory myopathy patients seen at a tertiary Malaysian hospital, anti-SRP myopathy was seen a quarter of the patients. The clinical picture was similar to anti-SRP myopathy reported from other populations.