No Evidence that Variations in Ambient Solar Ultraviolet Radiation and Psoriasis Severity are Associated

Background: Seasonal variability in psoriasis severity may be related to changes in unintentional or intentional exposure to ultraviolet radiation (UVR), or more intensive medication use during summer. Objective: Change in psoriasis severity for placebo-randomized subjects in clinical trials of moderate–severe psoriasis, as a function of estimated change in ambient UVR exposure, allows assessment of temporal changes in UVR on psoriasis without confounding from therapies that are prohibited during trial conduct. Methods: Placebo-randomized subject data, including dates and PASI for baseline and Week 16 visits, and approximate investigator location, pooled from the placebo-controlled double-blinded periods (Weeks 0–16) of 3 moderate–severe psoriasis clinical trials, were accessed through the Vivli data platform. Investigator locations were geocoded and linked to estimated mean daily ambient erythemally weighted UVR for the months corresponding to baseline and Week 16, using data from the Ozone Monitoring Instrument on board the NASA EOS Aura spacecraft. Results: Simple linear regression of percentage PASI change for 542 placebo-treated subjects with non-missing observations yielded a beta coefficient for percentage change in UVR of −0.009 (standard error = 0.008), with p = 0.243 and adjusted R² = 0.0007. Lack of statistical significance was observed across multiple regression analyses adjusting for baseline covariates and for interaction terms, and for mean difference in percentage change UVR for PASI50 responders versus non-responders. Conclusion: Multiple analyses failed to provide evidence that temporal variations in ambient UVR are associated with variations in psoriasis severity.