493 Non-contact reading of patch tests utilizing infrared imaging

Abstract

Patch testing of contact allergens to diagnose allergic contact dermatitis (ACD) is a traditional, useful tool. Reading the test shows high inter-individual variation between readers. During manual reading, the morphology of each contact allergen application site is evaluated by taking erythema, infiltration, vesicles and demarcation into account. The most important decision during reading of the patch test is the distinction between allergic and irritant reactions, as this has direct implications on the diagnosis of the patient. We aimed to evaluate a new method of non-contact infrared reading of patch tests. Following from this, a possible correlation between the intensity of the reaction and the increase in temperature was sought. 14 consecutive patients with 30 positive lesions were included in our study. Independent patch test readers assessed the reactive lesions and graded them allergic (of intensity + to +++) or irritant. At the same time, a forward-looking infrared (FLIR) camera attachment for iOS was used to acquire infrared thermal images of the readings. The photos were analyzed by the FLIR ONE app. Allergic patch test reactions showed temperatures increases of ≥ 0.7°C compared to surrounding skin. Irritant reactions however only resulted in ≤ 0.3°C temperature increase. Interestingly, the amount of the temperature increase did not correlate with the clinical intensity of the reaction. Thermography in evaluating erythematous lesion in patch testing demonstrated that allergic reactions seem to generate more heat that irritant reactions. With currently available devices, workflows could be established for half-automated, non-contact reading of patch tests. camera is an easy-to-use tool that can assist the physician in making a decision in difficult cases. Further studies are needed to confirm our findings.