Inflammatory myopathy with anti-SRP antibodies: case series of a South Australian cohort

Myopathy associated with anti-signal recognition particle (SRP) antibodies is a rare form of myopathy, which is thought to be distinct from classic polymyositis. We sought to determine the demographic, clinical and histopathological features of patients with anti-SRP antibodies. Hence we undertook an audit of patients with histologically-confirmed myositis who had anti-SRP antibodies. Of 144 patients with inflammatory myositis tested for myositis-specific and myositis-associated antibodies between 2007 and 2011 inclusive, five with anti-SRP antibodies were identified. All five were male, four had severe proximal weakness, one was asymptomatic and three had dysphagia. None had cardiovascular involvement. All patients showed isolated anti-SRP positivity and absence of antinuclear antibodies. Muscle histopathology showed variable myofibre necrosis, and most had an inflammatory infiltrate. Majority showed a favorable response to combination immunosuppressive therapy. Myopathy associated with anti-SRP antibodies is clinically heterogeneous in presentation. Muscle histopathology shows a mixture of necrotic and inflammatory features.