EMLA cream for pain reduction in diagnostic allergy skin testing: effects on wheal and flare responses.

Abstract

The use of a topical anesthetic cream containing prilocaine and lidocaine (EMLA) has been considered to reduce the pain of diagnostic allergy skin testing, but the effects of the cream on interpretation of skin tests is unclear. To determine the effects of the cream for pain reduction using prick and ID skin tests and for possible alteration of wheal and flare responses to allergen, saline, and histamine. In a randomized, double-masked, placebo-controlled design, 20 adult volunteers with a history of positive allergen tests had EMLA and placebo cream placed according to the manufacturer's recommendations on the volar aspect of the arms. Paired skin tests were placed and subjects rated the tests on a pain scale from 0 to 5 and average wheal and flare diameters were determined. Mean pain scores (+/-SEM) were significantly reduced from 2.5 +/- 0.7 to 1.1 +/- 0.6 for prick tests (n = 20, P < .001) and from 3.2 +/- 0.9 to 1.13 +/- 0.9 for intradermal (ID) tests (n = 58, P < .001). The wheal sizes for allergen prick tests, allergen ID tests, and histamine ID tests were identical in comparing placebo to EMLA-treated skin. Flare responses were reduced on the actively treated skin, on average, as follows: allergen skin tests- 52% (P < .001), and histamine- 40% (P < .001). In nine tests there was complete suppression of the flare response, all on the EMLA treated skin. EMLA significantly reduced the pain associated with diagnostic allergy skin testing and with no effect on the size of the wheal response. It reduces the flare response, in some cases inhibiting it completely, which must be taken into consideration in interpreting results.