Topical dermal anaesthesia inhibits the flare but not the weal response to allergen and histamine in the skin‐prick test

Abstract

The effect of topical dermal anaesthesia on the immediate allergic skin reaction was evaluated in a double-blind, randomized, placebo-controlled study. Twenty-one patients with strictly seasonal allergic rhinitis, confirmed by a positive skin test for the respective pollen allergen, were studied in the pollen-free winter months. Skin-prick tests for one pollen allergen and histamine were performed after pre-treatment of the skin for 1 hr with an emulsion of lidocaine and prilocaine (EMLA) and the equivalent vehicle on different test sites. The skin-prick tests were made with a preloaded standardized test needle (Phazet). The area of the induced weal-and-flare reaction was measured and subsequently calculated with the help of a digitizer served by a microcomputer. The topical dermal anaesthesia induced reduction of the flare response to histamine by 49% (P < 0.01) and allergen by 21% (P < 0.05). No reduction of the histamine- and allergen-induced weal response were noted. Our findings indicate that the treatment did not affect the allergen-induced release of inflammatory mediators and the vascular leakage induced by these mediators. However, this study seems to confirm earlier suggestions that the flare response is partly mediated through neural reflex activity as it was ameliorated by topical anaesthesia. Furthermore, from a clinical point of view, this study shows that it is possible to perform a valid skin test, without any associated itching and pain, if only the weal response is taken into account in the evaluation of the skin-prick test.