THE IMMUNOFLUORESCENT PROFILE OF DERMATOMYOSITIS - A COMPARATIVE-STUDY WITH LUPUS-ERYTHEMATOSUS

We have demonstrated a role for microvascular injury mediated by the m embrane attack complex of complement (C5b-9) in the genesis of cutaneo us lesions of dermatomyositis (DM) (1). The purpose of this study is t o revisit the immunofluorescent (IF) profile of DM, to further investi gate the role of C5b-9 in the pathogenesis of cutaneous lesions, and t o see if any features of tile IF profile reliably distinguish DM from LE. Lesional skin biopsies from 24 patients with clinical findings cha racteristic of DM were received in formalin and in Michel's transport medium. Conventional light microscopy, and IF studies with antibodies monospecific for IgG, IgA, IgM, C3, fibrin and C5b-9 were performed. T he control group comprised biopsies from 31 patients with well-documen ted LE. A positive lupus band test (LET) correlated highly with a diag nosis of LE, with a sensitivity of 64.5% and a specificity of 95.6% (p =0.001). The LBT was most sensitive in the setting of DLE and SLE and was least sensitive in the setting of SCLE. The finding of vascular C5 b-9 deposition correlated with a diagnosis of DM versus LE(P=0.001) al though the false positive rate was 21.4%. The false negative rate was reduced when vascular C5b-9 was seen in the absence of antibodies to R o, La, or RNP. While a nepative LET correlated with a diagnosis of DM (p=0.001), the specificity was only 64.5%. However when it was seen in concert with C5b-9 along the DEJ, specificity was increased to 80.6% (p=0.001). The presence of C5b-9 in vessels and along the DEJ in conce rt with a negative LET was predictive of DM (p=0.001) with a specifici ty of 93.5%, sensitivity of 78.3%, a false positive rate of 10% and a false negative rate of 14.7%. The combination of a negative LET, vascu lar C5b-9 deposition and negative serology for Ro, La, and RNP was a p redictor of DM versus LE with a sensitivity of 90.5%, a specificity of 96.8%, a false positive rate of 5% and a false negative rate of 6.2% (p=0.001). The IF profile of DM in lesional skin comprises a negative LET, deposition of C5b-9 within vessels and along the DEJ, and variabl e keratinocyte decoration for IgG and C5b-9 The most statistically pow erful predictor of DM is the combination of a negative LET with vascul ar C5b-9 deposition and negative serology for antibodies to Ro,La, Sm, and RNP. Demonstration of a negative LET in all but 1 case of DM sugg ests that the DEJ is not a primary site for antigen-antibody interacti on. We postulate that the aforementioned IF findings reflect he morall y mediated injury of endothelium and keratinocytes, effected by C5b-9. (C) Munksgaard 1997.