Necrotizing Myopathies: A Myopathology Experience from a Single Tertiary Care Center

BACKGROUND AND OBJECTIVES: Necrotizing myopathy (NM) is a rare inflammatory myopathy characterized by prominent necrosis and minimal to absent inflammation, arising from heterogeneous immune- and non-immune-mediated causes. Muscle biopsy aids diagnosis, especially in seronegative cases and those with overlapping presentations, helping to distinguish NM from other idiopathic inflammatory myopathies (IIMs). This tertiary center study examines the myopathologic spectrum in NM, correlating histopathologic findings with clinical features and autoantibody profiles. METHODS: We studied the records and biopsies of 77 patients diagnosed with NM between June 2023 and December 2024. Clinical and myositis antibody data were obtained from the records. The biopsies underwent histologic evaluation, including enzyme histochemistry and immunohistochemistry. Descriptive statistics and Chi-square tests (GraphPad Prism 9.5.1) were used to assess features across etiologies. RESULTS: This study included 77 patients (median age, 51 years; M:F, 2.4:1) with a mean creatine phosphokinase of 21,230 IU/L. All presented with acute/subacute proximal weakness ( n = 77, 100%), while myalgias ( n = 20, 25%) and fever ( n = 17, 22%) were less common. Identified etiologies included statin-associated myopathy ( n = 19, 24.6%), infections ( n = 22, 28.5%), anti-signal recognition particle myopathy ( n = 7, 9%), anti-hydroxy-3-methylglutaryl-coenzyme A reductase myopathy ( n = 4, 5.1%), others (overlap syndromes, alcohol-related myopathy, lipid storage myopathy, etc.), and idiopathic cases ( n = 15, 19.4%). Biopsy findings included scattered necrotic fibers ( n = 48, 62%), groups of necrotic fibers ( n = 29, 37.6%), fiber regeneration ( n = 52, 67.5%), perivascular inflammation ( n = 11, 14.2%), endomysial inflammation ( n = 4, 5.1%), and major histocompatibility complex class I (MHC-I) expression that was diffuse positive ( n = 22, 28.5%), focal positive ( n = 26, 33.7%), or negative ( n = 19, 24.6%). MHC-I expression significantly discriminated among etiologies ( P = 0.0013), unlike patterns of necrosis or inflammation ( P > 0.20). CONCLUSIONS: NM encompasses diverse immune- and non-immune-mediated causes that share similar biopsy features, distinct from those of other inflammatory myopathies. Accurate diagnosis requires clinicoseropathologic correlation.