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Clinical Images of Positive Diagnostic Challenge Tests.
Positive diagnostic challenge tests are shown for four common chronic inducible urticaria syndromes: dermatographia, characterized by a linear wheal–flare reaction elicited with light stroking of the volar surface of the arm with a tongue blade (Panel A); cold urticaria, characterized by raised swelling, which is demarcated from normal skin after application of an ice pack (Panel B); cholinergic urticaria, which has the appearance of a satellite wheal (arrow) after intradermal injection of methacholine (circle) (Panel C); and delayed pressure urticaria, as illustrated by an indurated, swollen area that developed at the site of, and 6 hours after, a pressure stimulus in the patient shown in Panels D and E.