Anti-SRP myositis: a diagnostic and therapeutic challenge.

Background: Anti-signal recognition protein (anti-SRP) myopathy is a rare idiopathic inflammatory myopathy in children. Herein, a 3-year-old patient with severe anti-SRP myopathy showing a rapidly progressive disease course is presented in order to increase the awareness of pediatricians about idiopathic inflammatory myopathies.

Case Presentation: A previously healthy 3-year-old girl presented with progressive symmetrical proximal muscle weakness that caused difficulty in climbing stairs for two months prior to evaluation, and a marked elevation of the serum creatine kinase levels. A skeletal muscle biopsy revealed necrotic and regenerating processes, with mild inflammatory changes. Myositis-specific and associated autoantibodies tested by the immunoblot method were positive for anti-SRP. Pulse corticosteroid, intravenous immunoglobulin, and methotrexate were administered. However, muscle weakness progressed, respiratory distress and dysphagia developed. Rituximab was initiated. While on rituximab treatment, she was able to walk independently and muscle enzymes were within normal range at the 15th month of diagnosis.

Conclusion: Early diagnosis of patients with anti-SRP myositis is important to control inflammation and prevent disease progression and complications. To our knowledge, our patient is the youngest case reported in the literature and was successfully treated with rituximab added to conventional therapy.