Diagnostic, prognostic and pathogenic value of the direct immunofluorescence test in cutaneous leukocytoclastic vasculitis

Background No precise studies have been performed on cutaneous leukocytoclastic vasculitis (LV) to establish whether it is better to obtain a skin biopsy from lesional or from perilesional skin for direct immunofluorescence (DIF). There is no agreement on the immunoglobulins most frequently detected and the value of DIF for the classification of cutaneous vasculitis. Methods A prospective study of DIF in lesional and perilesional skin was performed in 50 leukocytoclastic vasculitis patients and 15 nonvasculitis patients. Results We detected a higher level of positivity in involved skin than in uninvolved skin for IgG, IgA, IgM, C3 and fibrinogen but not for C1q. In vasculitic patients, IgA was the immunoglobulin most frequently detected in lesional (82%) and perilesional skin (68%), followed by IgM (56 and 34%, respectively) and IgG (20 and 8%, respectively). Only IgA deposits were associated with the diagnosis of vasculitis, with a sensitivity of 82% in lesional and 68% in perilesional skin, and with a specificity of 73 and 66.7%, respectively. The presence of IgA in lesional skin was associated with renal involvement but there was no association with severity. The presence of IgG or IgM, or the absence of IgA in perilesional skin was related to the presence of cryoglobulins. The absence of IgA in lesional and perilesional skin was also related to hepatitis C virus infection. Conclusions DIF findings in involved skin are more closely related to the diagnosis of vasculitis and can give more information about overall renal involvement than findings in uninvolved skin. However, findings in uninvolved skin are more closely related to the pathogenic factors that trigger the development of vasculitis.