Eosinophilic infiltration: an under-reported histological finding in urticarial vasculitis.

Abstract

Urticarial vasculitis (UV) is a clinicopathologic entity in which skin lesions resemble urticaria clinically but last more than 24hours and resolve with residual purpura. In this study, we evaluated distinguishing histological features of UV from common urticaria to differentiate between these two entities. During 1 year, 55 urticaria and 245 UV samples were assessed. The selection criteria for UV included: (1) samples that the histological diagnosis was confirmed by two independent dermatopathologists, (2) the histological diagnosis of UV was inconsistent with the first clinical impression and lesion characteristics. Of our 245 UV patients, 96% had endothelial swelling, 18% had red blood cell (RBC) extravasation, neutrophilic infiltration was seen in 46.7%, and perivascular, interstitial, and perineural eosinophilic infiltration in 198 (81.8%), 181 (74.2%), and 118 (48.1%), respectively. Among different histological findings, endothelial cell swelling as well as neutrophil around vessels and eosinophilic infiltrations were statistically different between two groups (P-value˂0.001). Both urticaria and UV samples showed a predominantly lymphocytic infiltration more than 10 cells per high power field (HPF) (98.2% of urticaria, 98.8% of UV), and only two patients (0.8%) with UV had predominant neutrophilic infiltration (more than 10 cells/HPF). We have found that both urticaria and UV showed a predominantly lymphocytic infiltration along with RBC extravasation, endothelial cell swelling, and fibrin deposition in UV. Moreover, significant perineural, perivascular, and interstitial infiltration of eosinophil in UV lesions compared to urticaria was another point that indicates special contribution of these cells in UV pathogenesis.