S.J. Arnold, J. Reed
Dermographic urticaria is characterised by an exaggerated triple response, such that ﬁ rm stroking of the skin results in a normal or increased wheal and ﬂ are reaction, accompanied by disproportionately severe itch. Although previously named factitious urticaria, symptomatic dermographism appears to have an immunological basis, since it can be transferred when patients’ IgE is injected into normal recipients. Although dermographic urticaria is one of the more common physical urticarias, it is only very rarely associated with systemic symptoms, and has not previously been reported as a cause of anaphylaxis. We report two cases of dermographic urticaria that presented as idiopathic anaphylaxis.
In the ﬁrst case, a well young man developed repeated episodes of anaphylaxis after using a ‘power shower’, requiring multiple hospital admissions and frequent use of an adrenalin auto-injector. In the second case, an otherwise well middle-aged man developed severe scalp itch; scratching resulted in progressive extension and generalisation of the itch, with the development of linear wheals, uncontrolled scratching and then anaphylactic symptoms. He had several further episodes of milder generalised itch followed by linear wheals after scratching. Both cases had normal full blood counts, complement C4 levels, mast cell tryptase, thyroid function and inﬂ ammatory markers. Both cases had a brisk dermographic response, but were negative to other relevant physical provocation tests, including for aquagenic urticaria in case one. Both patients responded to high-dose antihistamine therapy and lifestyle modiﬁ cations such as changing the shower water pressure. These cases highlight the very rare but potentially life- threatening complications of dermographic urticaria.a