High-dose cyclophosphamide without stem cell rescue in immune-mediated necrotizing myopathies

OBJECTIVE: To describe the experience managing treatment-refractory immune-mediated necrotizing myopathies (IMNM) with high-dose cyclophosphamide (HiCy) therapy. METHODS: Five patients with severe refractory IMNM who were treated with HiCy without stem cell rescue were identified. Their medical records were reviewed to assess demographic, clinical, and histologic characteristics as well as response to therapy. RESULTS: Three patients with anti-signal recognition particle (SRP) and 2 patients with anti-HMG-CoA reductase autoantibodies were included. The mean follow-up time after HiCy therapy was 37 ± 28 months. Two patients demonstrated substantial response, evidenced by improved muscle strength and decreased muscle enzymes after HiCy therapy; both of these patients were anti-SRP positive. Four patients experienced febrile neutropenia after HiCy therapy, one of which required a prolonged intensive care unit stay for infectious complications, from which they eventually recovered. CONCLUSIONS: These data suggest that HiCy therapy without stem cell rescue may be considered as an alternative for the treatment of refractory IMNM.