PD07 Polymorphic light eruption: insights from a tertiary photodiagnostic service

Abstract Polymorphic light eruption (PLE) is the most common photodermatosis. It is typically characterized by seasonal delayed-onset induction of rash of variable morphology after sunlight exposure. This study investigated the demographic, clinical and photobiological characteristics of patients diagnosed with PLE at a UK tertiary photodiagnostic service over a 10-year period. A retrospective review of case notes and an in-house photobiology database was conducted for patients diagnosed with PLE between 2014 and 2024. Data from 430 patients (74% female) were included, with mean age of symptom onset at 26 years (range < 1–81) and a mean age at photodiagnostic assessment of 35 years (range 2–85). Most patients had skin phototypes I (31%) and II (46%) and presented with a history of a sunlight-induced papular eruption. Rash was triggered by exposure ranging from minutes to hours, with latency periods to rash onset ranging from immediate to 48 h. Rash duration varied from < 12 h (n = 12) to months (n = 4). One-quarter of patients reported the priming phenomenon. Systemic symptoms during episodes, including fatigue, malaise and headache, were reported by 7%. Symptoms occurring with light through window glass were common (53%), and 24% were affected through clothing. One patient reported symptoms due to artificial light and 7% reported PLE induction by sunbeds. Seasonal symptoms occurred in 76%, with 13% experiencing PLE only abroad and 10% having perennial symptoms. A history of atopy was present in 37%, 27% had allergic contact dermatitis and 3% had photoallergic contact dermatitis diagnosed through patch testing and photopatch testing. Vitamin D deficiency or insufficiency occurred in 59% of patients tested (n = 188). Adverse impact on quality of life was important, with a median Dermatology Life Quality Index score of 11 in this cohort. Phototesting revealed abnormal monochromator photosensitivity in 35%, with the ultraviolet A waveband most frequently implicated. Iterative broadband ultraviolet A provocation testing induced a papular response in 35% of 392 patients tested. In conclusion, this study provides a detailed analysis of a large cohort of cases of PLE assessed through a tertiary photodiagnostic unit over a recent 10-year period. The results highlight the significant adverse impact of PLE on quality of life, possibly compounded by delays in referral time for assessment. The findings emphasize the need to enquire about the priming phenomenon and systemic symptoms and to address vitamin D status. Possible associations with allergic contact dermatitis and atopy are notable and require further study. Interestingly, even in this selected cohort of patients with PLE referred to a tertiary service, phototesting is normal in most, emphasizing the need for careful clinical assessment in parallel with photodiagnostic investigations, to ensure accurate diagnosis.