Results of Photopatch Testing in Israel: A Retrospective Cohort Study.

Background: There are limited data regarding photopatch testing (PPT) in Israel. Objectives: To investigate the prevalence of positive reactions and concurrent diagnosis of patients that underwent PPT in a single center in Israel. Methods: Retrospective cohort study that included all patients that were suspected of having contact dermatitis and underwent patch testing with the European baseline series (EBS) and additionally were selectively PPT with the Scandinavian/European baseline photopatch series in a tertiary medical center in Israel (2009-2023). Results: Of 5234 consecutive patients tested with the EBS, 78 (1.5%) underwent PPT. Overall, 23 (29.49%) patients demonstrated positive PPT results, and 13 (56.52%; 17 positive reactions, 12 different allergens) exhibited clinically relevant reaction and were diagnosed with photoallergic contact dermatitis (PACD). Sunscreen-related allergens represented the most common relevant photoallergens (6 patients, 46.15%), with benzophenone-3 yielding positive and relevant results in 5 cases. The duration of symptoms was significantly (P < 0.05) longer among 13 patients with relevant PPT reaction that were diagnosed with PACD (12.16 ± 12.44 years) compared with patients with irrelevant (4.86 ± 6.75 years) or negative results (5.29 ± 7.98 years). The most common final diagnosis was allergic contact dermatitis (ACD) (21 cases, 26.92%), followed by PACD (13 cases, 16.66%), nonspecific dermatitis (5 cases, 6.41%), or atopic dermatitis (4 cases, 5.13%). About half (48.71%) of patients had indeterminate or other diagnoses, including rosacea, solar urticaria, polymorphic light eruption, and collagen vascular disease. Conclusion: In this retrospective Israeli study, the prevalence of positive PPT was relatively high (29%); however, falls within the wide range of reported values. Sunscreen-related allergens, specifically benzophenone-3, were the most common culprit. Among PACD patients, time-to-diagnosis was significantly delayed compared to other patients. Although the final diagnosis was heterogenous, ACD was the most common type.