PD04 Characterization of demographic, clinical and photobiological features of solar urticaria: a UK multicentre cross-sectional study
Authors: Thumber Navandeep K , McSweeney Sheila , Elsbahi Hana , McGrath Conn , Christou Evangelos A A , Walker Susan , Naik Harsha , Bintcliffe Keyna , Ibbotson Sally H , Weatherhead Sophie , Fityan Adam , Goulden Victoria , Rhodes Lesley E , Rutter Kirsty , Wagner Annette , Grattan Clive , Fassihi Hiva , Ferguson John , Sarkany Robert , Tziotzios Christos , Simpson Michael , McGrath John 
Published: June 2024

Abstract
Solar urticaria (SU) is a rare immunologically mediated photodermatosis caused by abnormal cutaneous mast cell degranulation following exposure to solar radiation. It manifests as the rapid development of erythemal flares, weals and/or angio-oedema following sunlight exposure and is associated with anaphylaxis-like symptoms in severe cases. Unsurprisingly, it has a significant impact on patients’ quality of life. As part of a genetic investigation of SU pathobiology, we have undertaken a descriptive cross-sectional study of the demographic, clinical and photobiological features of patients with SU recruited from six UK tertiary photobiology units. Clinical and genetic material were collected from participants following informed consent (19/EM/0312 and 07/H0802/104). Eligibility criteria were a diagnosis of SU made by a consultant dermatologist and confirmed by phototesting. Patients with comorbid porphyrin disorders were excluded. A standardized case report form was used to collect demographic, clinical and photobiological features. A descriptive and exploratory statistical ana­lysis was performed using the R statistical programme (R Foundation, Vienna, Austria). When data were missing for a participant, they were excluded from the relevant analysis. Of 178 included individuals, 66.9% were female and the mean age of disease onset was 36 years (range 1–82). Reported ethnicity was European in 90.2%, South Asian in 5.7%, East Asian in 1.1%, and African, Afro-Caribbean or mixed in 2.9%. Skin phototype was reported as phototype I (16.6%), phototype II (57.3%), phototype III (14.6%), phototype IV (4.5%), phototype V (5.1%) and phototype VI (1.9%). Photoprovocation was achieved using monochromator phototesting in 94.2%, while 5.8% could only be provoked using a solar simulator. Based on monochromator phototesting, the most common pathogenic waveband was ultraviolet A alone (28.1%). Among individuals with skin phototypes I–III, the most common pathogenic wavebands were ultraviolet A and visible light (29.9%), and among skin phototypes IV–VI, it was ultraviolet A and ultraviolet B (25.0%). Over half of the patients (57.3%) had coexisting atopic disorders (eczema, hay fever or asthma), while 15.2% had another photodermatosis, and 27.0% reported another type of urticaria. Sunscreen was used by 92.1% of patients, as were H1-receptor antagonists (92.1%), while 37.1% used H2-receptor antagonists, 44.4% used montelukast, and 20.2% used omalizumab. Of those treated with H1-receptor antagonists (n = 164), 75.0% reported that they were partially or completely effective. Omalizumab was reported to be completely or partially effective in 29 of 36 (81%) treated patients. In conclusion, this study summarizes the demographic and clinicophotobiological features of SU in the UK, while also highlighting the effectiveness of H1-receptor antagonist and omalizumab treatment in many cases.