Photopatch testing - a retrospective review using the 1 day and 2 day irradiation protocols

Photopatch testing is indicated in the investigation of patients with eczematous eruptions, affecting mainly light-exposed sites and in those who give a history of worsening of their condition with sun exposure. 3 different protocols are described by the British Photodermatology Group (Br J Dermatol 1997:136:371-376), 1 of which includes irradiation of allergens 1 day after application and 2 using irradiation of allergens 2 days after application. There is no evidence for superiority of any of these protocols. We reviewed the records of all patients who underwent photopatch testing in Leeds over a 50-month period, who had had the allergens applied in triplicate with 1 set irradiated after 1 day occlusion and another after 2 days. The control was occluded for 2 days. Readings were performed at 2 days and 4 days. 15 of 74 patients photopatch tested during this period had 49 positive results between them. 43 of these were felt to be of current relevance to their clinical problem. 34 of the positive results were indicative of photoallergy. Additional photoallergic reactions were detected following 2 days occlusion and irradiation compared with 1 day occlusion (16 versus 5). In conclusion, our case series suggests that 2 days occlusion before irradiation of allergens is more sensitive at detecting photoallergy.