Immune-mediated necrotizing myopathy which showed deposition of C5b-9 in the necrotic muscle fibers and was successfully treated with intensive combined therapy with high-dose glucocorticoids, tacrolimus, and intravenous immunoglobulins.

Currently, no standard treatment strategy has been established for immune-mediated necrotizing myopathy (IMNM). Here we present a case of IMNM which was successfully treated with intensive combined therapy with high-dose glucocorticoids, tacrolimus, and intravenous immunoglobulins. Her muscle weakness was rapidly progressive and severe so that she became bedridden one week after admission. She was complicated with dysphagia and had serum myogenic enzymes elevation, ventricular diastolic dysfunction, and interstitial lung disease. Serum anti-SRP antibody was positive and her muscle biopsy revealed many necrotic fibers with minimal inflammation. Further histological analysis demonstrated infiltration of phagocytic macrophages with deposition of membrane attack complex (C5b-9) in the necrotic muscle fibers, suggesting activation of complement pathway and macrophages as a pathomechanism of this disease. She was diagnosed as IMNM and was immediately initiated a combination therapy described above, which led to dramatic clinical improvements. Recent studies suggest that intravenous immunoglobulins and tacrolimus can inhibit the activation of complement pathway and macrophages. Our present case suggests that early initiation of intensive combined therapy including intravenous immunoglobulins and tacrolimus might be effective for preventing irreversible muscle damages by disrupting a pathogenic activation of complement and macrophages in IMNM.