Résumé :
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Necrotizing myopathy (NM) is an acquired condition histopathologically characterized by scattered necrotizing fibers at various stage of injury or healing (acute necrosis, myophagocytosis, basophilic fibers, centronucleation), with no or only minimal inflammation. NM usually was regarded as indicating a toxic or paraneoplastic origin. However, in number of patients, NM develops in the setting of autoimmunity and appears responsive to immunomodulatory drugs, leading myologists to delineate a new condition termed 'auto-immune NM' (AINM). However, in routine practising, the frontiers between AINM and polymyositis (PM) appear somewhat imprecise. We retrospectively evaluated patients with necrotizing myopathy diagnosed at Henri Mondor hospital between 2001 and 2007 according to muscle biopsy findings. Analyzed parameters included demographic data, associated conditions, CK levels and histopathological features, including immunohistochemical expression of MHC-1 (HLA-ABC) and -2 (HLA-DR), membranolytic attack complex (C5b-9), and PECAM/CD31 (endothelium). 728 patients were diagnosed as inflammatory/dysimmune myopathy of which 39 (5.4%) had necrotizing myopathy (NM). Sex ratio (M/F) was 29/13, mean age 51 yrs (range 20-82). Cancer was found in 4/39 (10%) and autoimmunity in 21/39 (54%), including systemic sclerosis 8/39 (20%), interstitial lung disease 4/39 (10%) and anti-SRP antibodies in 3/39 (8%). Mean CK level was 15xN (range: 1-100xN). Abnormal myofiber expression of CMH 1 was found in 79% of patients and was ubiquitous in 24%. Focal myofiber expression of CMH 2 was found in 29%. C5b-9 deposition was observed on capillaries in 79%, myofibers in 61%, and both in 55%. When performed, PECAM immunostaining showed focal capillary loss (16/17). In conclusion, necrotizing myopathy most often corresponded to a dysimmune condition with immunopathological pattern ranging from pure AINM to probable PM, and characterized by local C5b-9 formation. Understanding the exact role of complement activation in myofiber injuries could be of first importance by opening promising tracks for further therapeutic strategies.
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