DIAGNOSIS AND INCIDENCE OF DELAYED PRESSURE URTICARIA IN PATIENTS WITH CHRONIC URTICARIA

Background. The incidence of delayed pressure urticaria (DPU) may have been underestimated, particularly in patients with widespread wheals of concurrent idiopathic urticaria, because of difficulty in recognizi ng the association between pressure-related swellings and the precedin g physical stimulus. Diagnostic tests for DPU have not been done routi nely in studies of urticaria and have not been compared. Objective. Ou r purpose was to establish the incidence of DPU and other physical urt icarias in patients with chronic urticaria and to compare two reproduc ible pressure challenge tests. Methods: One hundred thirty-five patien ts were tested for immediate dermographism, for DPU and, when indicate d by the history, for cholinergic and/or cold urticaria. In patients w ith pressure-related symptoms, pressure challenge testing with a dermo graphometer (100 gm/mm2) was compared with a test that involves the ap plication of 1.5 cm diameter weighted rods and more closely resembles a naturally occurring pressure stimulus. Results. Physical urticarias were present in 96 patients (71%). Thirty patients (22%) had immediate dermographism, 50 (37%) had DPU, 15 (11%) had cholinergic urticaria, and 3 (2%) had cold urticaria. A 70-second pressure challenge with the dermographometer gave results comparable to the use of the weighted r ods. Conclusion: DPU appears to be more common in chronic urticaria th an previously reported and is present in some patients who do not repo rt pressure-related wheals.