Successful treatment of anti-signal recognition particle antibody-positive myositis with intravenous cyclophosphamide: A case report.

Myositis-specific autoantibodies play an important role on the disease phenotype of idiopathic inflammatory myopathies (IIMs). Anti-signal recognition particle (SRP) antibody-positive patients with IIMs may present with severe myopathy and highly elevated serum creatine kinase levels. These patients are often resistant to immunosuppressive therapy, but there is no established treatment strategy. A 51-year-old man referred to our department was diagnosed with IIM based on imaging and pathological findings. A high dose of corticosteroids followed by intravenous cyclophosphamide (IV-CY) treatment (750 mg three times) resulted in an improvement in clinical manifestations and functional outcomes, and recurrence did not occur. Our case suggests that IV-CY is an effective induction regimen for patients with anti-SRP antibody-positive IIMs.