Long-Term Observations on the European Photopatch Test Baseline Series (EPTBS) in Real Clinical Practice: 11 Years of Results in a Spanish Cohort and Suggestions for an EPTBS Update

The European Photopatch Testing Baseline Series (EPTBS) was published in 2013. However, limited data exist regarding the real-world clinical application of the EPTBS. This study aims to describe the photopatch test experience with the EPTBS over 11 years at a tertiary hospital in Spain. A retrospective chart review spanning from February 2012 to October 2023 was conducted on patients who underwent photopatch testing (PPT) with the EPTBS. Additionally, patch testing was performed on all patients according to the European recommendations. Data from 148 patients were collected, and showed a PPT positivity rate of 7.4% (n = 11). Specifically, we found a photoallergic contact dermatitis (PACD) in 11/148 patients (15 positive reactions to 8 different allergens, including one patient own's product). Of them, 87% had current relevance and non-steroidal anti-inflammatory drugs (NSAIDS) were the main culprits of PACD (60%). Alternatively, we found a contact allergy to the EPTBS allergens in 14/148 (9.3%) patients, (21 positive reactions both in the irradiated and non-irradiated set to 17 different allergens, including many patients' products). Of them, UV solar filters represented the main cause of ACD. Regarding the patch testing results, we observed a positivity rate of 39.9% (116 positives in 59 different patients). The most frequent were methylchloroisothiazolinone/methylisothiazolinone, fragrance mix I and II and Myroxylon pereirae resin (balsam of Peru). EPTBS implementation has permitted a more accurate study of PACD. Our positivity rate for PPT is slightly lower than previous reports, however the main culprits for PACD remain to be NSAIDS. The inclusion of contact allergens applied in photoexposed areas in the EPTBS could contribute to discriminating between PACD, photoaggravated ACD and ACD.