Class I MHC detection as a diagnostic tool in noninformative muscle biopsies of patients suffering from dermatomyositis (DM)

This study is to further confirm the diagnostic value of class I MHC detection in muscle biopsies of adult patients presenting with clinical features of dermatomyositis (DM) and to address its diagnostic value in the case of nonspecific biopsies. A retrospective study was performed on muscle biopsies in 22 patients presenting with clinical features of DM. Immunohistochemical detection of class I MHC was performed in all cases. On pathological features two groups of patients were recorded: group I (14 patients) with typical features of DM and group II (eight patients) with almost normal muscle biopsies (no inflammatory exudates, no perifascicular atrophy). Abnormal sarcolemmal class I MHC expression was recorded in all cases. In all muscle biopsies of group I patients, class I MHC expression was observed in almost all fibres but was stronger in perifascicular areas (eight patients) or was restricted to perifascicular atrophic fibres (six patients). In all muscle biopsies of group II patients, only some perifascicular fibres expressed class I MHC. According to Bohan and Peter criteria, patients were classified as definite DM (nine group I and three group II patients), probable DM (five group I and two group II patients) and possible DM (three group II patients). Abnormal perifascicular class I MHC expression is of diagnostic value in patients presenting with clinical features of DM especially when muscle biopsy fails to show typical features such as inflammatory infiltrates and/or perifascicular atrophy.