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.

Anti-signal Recognition Particle Antibody-positive Necrotizing Myopathy with Secondary Cardiomyopathy: The First Myocardial Biopsy- and Multimodal Imaging-proven Case

A 69-year-old Japanese woman was admitted to our hospital with progressive muscle weakness and dysphagia. She was taking pitavastatin for dyslipidemia. Her serum creatine kinase was 6,300 U/L. Pitavastatin was stopped, but her symptoms deteriorated, and cardiac congestion appeared. A muscle biopsy showed necrotizing myopathy (NM), and anti-signal recognition particle (SRP) antibody was positive. ¹⁸F-fluorodeoxyglucose-positron emission tomography showed an abnormal uptake, and magnetic resonance imaging showed abnormal gadolinium enhancement in the left ventricular wall. An endomyocardial biopsy revealed inflammatory cardiomyopathy. Steroid, tacrolimus, and intravenous immunoglobulins were effective against the symptoms. This is the first case of biopsy-proven secondary cardiomyopathy due to anti-SRP-positive NM.