Clinical observations on delayed pressure urticaria

Repeated pressure tests at regular intervals were carried out on 48 patients with delayed pressure urticaria (DPU). Patients showed a considerable variation in response with periods of positive testing ranging from a few days to months or years. All the DPU patients had had chronic urticaria and/or angio-oedema although sometimes minor and occasional. Pressure tests were also carried out at regular intervals on seven patients with chronic urticaria who had weals at pressure sites but no history of pressure-induced weals (Köbner weals). These weals coincided with positive pressure tests and it seems likely that they all had DPU but only for a short time. Delayed dermographism was studied in eight patients with DPU. There was a good correlation in time and degree between positive pressure tests and delayed dermographism, confirming that delayed dermographism is in fact DPU provoked by a slightly different mode of pressure.