Delayed pressure urticaria histologically resembles cutaneous late-phase reactions

In a recent study, all patients with delayed pressure urticaria (DPU) developed late cutaneous reaction (LCR) after intradermal injection of compound 48/80 and after skin testing with certain food antigens. In the present study, we analyzed the histologic changes in the pressure lesions and compared them with those found in normal skin injected with diluent and in LCR to 48/80. The study included five patients with DPU associated with chronic urticaria (CU) and four patients with CU but without DPU. Six to eight hours after pressure challenge and intradermal skin testing with 48/80 and diluent, skin biopsy specimens were obtained from the pressure lesions, the LCRs, and normal skin (diluent injection). Specimens were assessed by Giemsa staining of 1-micron sections and immunofluorescence of frozen sections. Total cells were counted in each specimen. Interstitial deposits of fibrin were observed by immunofluorescence in LCR and pressure lesions. The total numbers of infiltrating cells in the dermis among LCR sites and pressure lesions were not significantly different, while both LCR sites and pressure lesions contained significantly more infiltrating cells than did normal skin injected with saline diluent. The differential counts in LCR and DPU were mostly mononuclear cells. Infiltrates in the DPU and LCR were mostly perivascular. No histopathologic changes were seen at skin sites challenged with pressure in the control patients with CU without clinical manifestations of DPU. We conclude that lesions seen in DPU are morphologically similar to classic LCR.