Abstract
OBJECTIVE: This study aims to describe the muscle biopsy features of overlap myositis (OM) and compare them with other inflammatory myopathies. We analyzed clinical, serological findings, and histopathological patterns in muscle biopsies to understand the features of OM. METHODS: Muscle biopsies submitted from patients diagnosed with OM between January 2023 and October 2024 at Nizams Institute of Medical Sciences, Hyderabad were recruited in this study. The clinical and myositis antibody details were noted. The biopsies underwent histological evaluation, including serology, enzyme histochemistry, and immunohistochemistry. RESULTS: The study cohort included 26 OM patients who underwent muscle biopsy. The female:male ratio is 25:1. The clinical diagnoses of the patients were systemic lupus erythematosus in 12, systemic sclerosis in 5, rheumatoid arthritis in 1, and mixed connective tissue disorder in 2. CPK levels were high in 24 patients. Anti-Ro52 antibodies were present in 18 patients. Biopsy revealed perivascular inflammation (17), myofiber necrosis (21), and myophagocytosis (7) with infrequent perifascicular atrophy (3). MHC-I expression was noted in all biopsies. CONCLUSION: We report on the muscle biopsy findings in patients with OM. The features align with the ENMC category of "non-specific myositis" with perivascular inflammation, fiber degeneration and regeneration, and sarcolemmal MHC Class 1 expression being the defining features.