High prevalence of necrotizing myofibers in adult dermatomyositis muscle biopsies

Introduction/objectives: This study aimed to analyze the presence, grade, and relevance of myofiber necrosis in the muscle tissues of patients with adult dermatomyositis. Second, these parameters were associated with the patients’ demographic, clinical, and laboratory data. Method: This was a retrospective study, from 2001 to 2021, which included 89 muscle biopsies of patients with definite dermatomyositis performed at the time of diagnostic investigation. Immunohistochemical analysis was performed on serially frozen muscle sections. The presence and degree of endomysial/perifascicular myofiber necrosis were also analyzed. The degree of necrosis was semi-quantitatively coded as absent/mild, moderate, or severe. The presence or absence of perifascicular atrophy and also perivascular lymphomononuclear infiltration was also evaluated. Results: Muscle biopsies from 89 patients, the majority of whom were Caucasian women, were evaluated. Both perifascicular atrophy and perivascular lymphomononuclear infiltrates were observed in 76 (85.4%) samples. Moderate or intense areas of myofiber necrosis in endomysial/perifascicular areas were found in 30/89 (33.7%) and 14/89 (15.7%) muscle biopsies, respectively, with a predominance of macrophagic infiltrate in relation to lymphomononuclear cells in these regions. The degree of muscle weakness in the limbs (upper and lower) was associated only with areas of intense myofiber necrosis. Conclusions: A high prevalence of myofiber necrosis was observed, which patients resembled the initial clinical feature of patients with immune-mediated necrotizing myopathies.Key Point• A high prevalence of myofiber necrosis was observed in muscle biopsies of patients with dermatomyositis