Résumé :
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Communication n° 325 Idiopathic inflammatory myopathies mainly include dermatomyositis, polymyositis, and inclusion body myositis. In PM and IBM, clonally expanded cytotoxic CD8 T-cells infiltrate muscle and are directed against MHC-I antigens expressing myofibers. However, in some clinically suspect patients, biopsy show diffuse myofibers MHC-I expression, without clear CD8 T-cells infiltrate. FC analysis of lymphocytes extracted from muscle allows to survey a much more important volume of tissue than could possibly be examined by slide analysis alone, and also provides accurate quantification of lymphocyte subsets. We propose to evaluate usefulness of FC for the diagnosis of inflammatory myopathies. Fourty-eight patients undergoing muscle biopsy for diagnosis purpose were included. In addition to myopathological examination, FC analysis of T-cell subsets in blood and muscle was performed to detect CD8+ T-cell enrichment in muscle. Muscle biopsy disclosed inflammatory myopathy in 11/48 (4 PM; 1 IBM; 3 DM; 2 granulomatous myositis; 1 connective tissue disease), various non-inflammatory changes in 22/48, and histologically normal muscle in 15/48. In patients with normal muscle, CD8 M/B ratio (meanÆSD) was 1.0Æ0.16 (95% c.i.: 0.90-1.09). In patients with inflammatory myopathies, CD8 M/B ratio was increased (2.3; range: 4.31-0.857; p=0.0003), including DM (mean CD8 M/B ratio in DM: 3.34). In patients with non-inflammatory changes, mean CD8 M/B ratio was 1.25 (NS). Conclusion: (1) T-cell phenotyping by FC applied to skeletal muscle is an innovative procedure; (2) normal value of CD8 M/B ratio is 1 (confidence interval: 0.9-1.09); and (3) inflammatory myopathies are characterized by increased CD8 M/B ratio assessing muscle enrichment in CD8 T-cells.
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