Résumé :
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INTRODUCTION Idiopathic inflammatory myopathies are a heterogeneous group of diseases including dermatomyositis, polymyositis and inclusion body myositis. It'simportant to diagnose these entities because they are potentially treatable. The aim of our study is to demonstrate the usefulness of the expression of MHC- I antigenin muscle sarcolemma as a key marker to the diagnosis of idiopathic inflammatory myopathies. MATERIAL AND METHODS This is a retrospective study carriedout on 06 muscle biopsies including 02 dermatomyositis, inclusion body myositis, non-specific myositis, dystrophy myopathy and a normal sample. All samples werefixed in isopentane, cooled with liquid nitrogen. They were stained with Hematoxylin-Eosin, Gomori Trichrome, SDH and DPNH. An immunohistochemical study withantibody anti-HLA I (clone W6/32, Dako) was performed to all samples using Ventana BenchMark immunohistochemistry automated machine. RESULTS 1-2) 37 yearold woman and 67 year old man. Muscle biopsy showed variation of the muscular fiber size, with a peri-fascicular atrophy, presence of vacuolated cells, associatedwith a mononuclear inflammatory infiltrate in the perimysium. The IHC study objective an overexpression of MHC-I antigen in all muscle sarcolemma. The diagnosisof dermatomyositis was established. 3) 68 year old, woman. Microscopic examination found an unequal fiber size and the presence of fibers with rimmed vacuolesin Gomori trichrome. The IHC study objective in some areas an important muscular sarcolemma expression for MHC-I.The diagnosis of inclusion body myositis wasproposed. 4) 48 year old man. The morphological study was sub-normal, without evidence of inflammatory involvement, but with pathognomonic clinical features ofdermatomyositis. The IHC study found an overexpression of muscular fiber sarcolemma for the MHC-I. The diagnosis of nonspecific myositis was established. 5-6)The IHC study performed to the dystrophic and normal samples, didn't find any expression for MHC-I. DISCUSSION - According to some authors, it is important to findthe mononuclear cells in muscle sarcolemma to establish the diagnosis of inflammatory myopathy. - However, some toxic or dystrophic diseases may be associatedwith inflammation infiltrate, leading to an incorrect diagnosis. However, in some cases with the presence of patent clinical signs of inflammatory myopathy, the musclebiopsy can be sub-normal, without the presence of inflammatory cells. Therefore, it's important is these cases to use some techniques more specific and sensitive asimmunohistochimistry to find a reliable diagnostic. CONCLUSION Our study clearly shows that the expression of Major Histocompatibility Complex I is a great help inthe diagnosis of idiopathic inflammatory myopathies, especially in cases where morphology and / or clinical signs are poor or atypical. The correlation between clinical,biological, morphological and immunohistochimical results remains the gold standard for a reliable diagnosis.
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