Preliminary ultrastructural analysis suggests phenotype-specific myofiber alterations in idiopathic inflammatory myopathies
摘要
Idiopathic inflammatory myopathies (IIM) comprise a heterogeneous group of autoimmune muscle diseases with variable patterns of muscle damage. In this multicentric cross-sectional study, we employed scanning electron microscopy (SEM) to characterize ultrastructural alterations in muscle biopsies from quadriceps (n = 29) and deltoid (n = 41) of 70 IIM patients classified by ENMC (European Neuromuscular Centre) 2004/2011/2023 and EULAR/ACR (European League Against Rheumatism / American College of Rheumatology) 2017 criteria, together with 8 control samples. Qualitative assessment revealed loss of hexagonality and fiber size variability across all samples, while porosities, ruptures, perforations, and sarcolemma remnant emerged as candidates to phenotype-specific distribution. Dermatomyositis (DM) presented relatively preserved ultrastructure, immune-mediated necrotizing myopathy (IMNM) exhibited perforations, and inclusion body myositis (IBM) displayed sarcolemma remnant. Perforations were linked to necrosis, whereas fatty replacement was less frequent in samples with ultrastructural alterations. Quantitative morphometry showed higher variability in quadriceps compared with deltoid fibers, and Z-score normalization confirmed widespread myofiber atrophy across IIM subtypes. Building upon previous preliminary observations, this study expands SEM-based analysis to a larger multicentric cohort, revealing preliminary phenotype-specific ultrastructural signatures that may contribute to a better understanding of the pathophysiological mechanisms of muscle damage in IIM.