Acetylcholine-induced whealing in cholinergic urticaria – what does it tell us?

Abstract Background Cholinergic urticaria (CholU) is characterized by the occurrence of itchy wheals induced by sweating. Intradermal injections of acetylcholine (ACh) have been proposed to help with diagnosing CholU and subgrouping of patients, but controlled studies are largely missing. Objective To compare the rates of positive ACh test results in well characterized CholU patients and controls and to identify clinical features of CholU linked to ACh reactivity. Methods Acetylcholine was injected intradermally into 38 CholU patients and 73 matched healthy controls. Wheal and flare skin responses were assessed after 15 and 30 minutes and correlated with clinical features of CholU. Results At 15 minutes after intradermal injections of ACh, wheal and flare responses were significantly more frequent in CholU patients than healthy controls, wheals: 37% vs.16% (P = 0.017); flares: 50% vs.19% (P = 0.005). Also, wheals were 168% and flares 52% larger and of longer duration in CholU patients than in healthy controls (both P  Conclusion Intradermal Ach testing does not allow for the identification of CholU patients due to its low sensitivity. ACh-induced wheals, in patients with CholU, is linked to sweating and longer lasting symptoms. Intradermal ACh testing is an interesting tool for mechanistic studies in CholU.