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 recognizing the association between pressure-related swellings and the preceding physical stimulus. Diagnostic tests for DPU have not been done routinely in studies of urticaria and have not been compared.

OBJECTIVE: Our purpose was to establish the incidence of DPU and other physical urticarias in patients with chronic urticaria and to compare two reproducible pressure challenge tests.

METHODS: One hundred thirty-five patients were tested for immediate dermographism, for DPU and, when indicated by the history, for cholinergic and/or cold urticaria. In patients with pressure-related symptoms, pressure challenge testing with a dermographometer (100 gm/mm2) was compared with a test that involves the application 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 rods.

CONCLUSION: DPU appears to be more common in chronic urticaria than previously reported and is present in some patients who do not report pressure-related wheals.