Solar Urticaria in 145 patients: Assessment of Action Spectra and Impact on Quality of Life in adults and children

Background. Solar urticaria (SU) is a rare chronic inducible urticaria triggered via uncharacterised chromophores. We detail responses of a large patient series to monochromator phototesting and broadband ultraviolet radiation (UVR); relationship to life quality is explored. Methods. Retrospective review of all SU patients undergoing standardised diagnostic photoinvestigation at a specialist centre during 2000-2016. From 2011, patients completed dermatology life quality index (DLQI) questionnaires for the past week and year. Results. In 145 patients (mean 35.8, range 3-69 years; 18 aged <18yrs; 100 female), combined phototesting with broadband UVR and monochromator sources successfully provoked 74.5% patients, with 65.6% provoked by broadband UVR alone and 57.9% by monochromated radiation alone. The narrow wavebands most frequently eliciting wheal and flare response were between 370-400nm, with 25% patients at 300±5nm, 53.6% at 320±10nm, 66.7% at 330±10nm, 77.4% at 350±20nm, 83.3% at 370±20nm, 86.9% at 400±20nm, 44% at 500±20nm, 17.8% at 600±20nm. In 62 patients, the DLQI revealed 56.1% had very to extremely large impact in the past week (all patients: mean score 11.1, range 0-29) rising to 69.8% for the past year (12.5, 0-30); adults and children were similarly affected. Patients with positive photoprovocation had higher DLQI score than those who were negative (DLQI for past week: mean 12.6 ± SEM 1.1 vs 4.6 ± 1.4, p<0.01). Conclusion. SU is predominantly provoked by longer UVA-shorter visible radiation, which penetrates window-glass and where sunscreens are less effective; impact on life quality is considerable. Photoprotective agents effective against this spectrum are needed.