PD11 Clinical features and prognosis of actinic prurigo in Scotland

Abstract Actinic prurigo (AP) is a rare chronic photosensitivity condition that typically presents in childhood and may resolve in adolescence. Although less frequent in adulthood, AP can present at this age and may be persistent. The aim of this study was to characterize the clinical presentation, investigation findings, disease course and prognosis of AP in Scotland. This was a retrospective review of patients with AP seen between March 2015 and December 2024 through the Scottish Photobiology Service (SPS). Data on disease characteristics, investigation findings and management were collected from the SPS database and patient records. In total 16 patients with AP were identified. Fifteen were female and one was male, and 11 were newly diagnosed. Ten (63%) had disease onset before age 16 years, with a median age of 10.5 years (range 1–50). Eight (50%) first presented in adulthood (> 16 years old). The most common acute eruption morphology was pruritic erythematous papules (70%). Among adult-onset cases, papulovesicular eruptions were most prevalent (67%). Half of the patients reported scarring. All patients had facial involvement, especially on the cheeks, nose and ears (44% each). Conjunctival involvement occurred in five (31%), and only three (19%) reported cheilitis. Nine (56%) were initially considered to have polymorphic light eruption (n = 5), hydroa vacciniforme (n = 2) or chronic actinic dermatitis (n = 2). Monochromator phototesting at presentation revealed normal action spectra in six (38%), with two developing monochromator ultraviolet (UV)A sensitivity over time. Four (25%) had UVA sensitivity only, four (25%) had UVB and UVA sensitivity and two (13%) had UVB, UVA and visible light sensitivity. Iterative UVA provocation testing showed papular reaction in six (38%), and abnormal erythema in another three (19%). Human leucocyte antigen (HLA) typing was available for 13 patients. Twelve (92%) were positive for HLA-DR4, with nine (75% with HLA-DR4) having the HLA-DRB1*0407 subtype. Twelve patients had follow-up visits, with a median follow-up of 10.8 years (range 1–28.4). Among seven young-onset cases, six (86%) showed marked improvement in clinical symptoms, with five (71%) having normalization of monochromator testing. In contrast, four of five patients (80%) with adult-onset AP remained symptomatic, with persistent abnormal phototesting. AP is a rare immunological photosensitivity disorder that is challenging to diagnose and must be kept in mind. The study found a higher than expected number of adult-onset cases, which tend to follow a more persistent course and are less likely to resolve spontaneously. HLA testing is a useful diagnostic marker, with particular utility in the more atypical adult-onset presentations of AP.