Broad-spectrum abnormal localized photosensitivity syndrome: a case report and literature review

Broad-spectrum abnormal localized photosensitivity syndrome (BALPS) is a rare photodermatosis characterized by recurrent cutaneous eruptions occurring at fixed body sites following ultraviolet (UV) radiation exposure. This report presents a case of skin phototype III in a 30-year-old woman who presented with a 7-year history of recurrent erythematous to violaceous, edematous plaques occurring exclusively on both buttocks during beach holidays. The eruptions were associated with burning and pruritus, occasionally progressing into vesicles or blisters. Each episode resolved within 1-2 weeks but resulted in post-inflammatory hyperpigmentation that persisted for several months. Phototesting demonstrated a reduced minimal erythemal dose (MED) to UVA and narrowband UVB on previously affected areas but normal responses to broadband UVA, broadband UVB, and visible light (VIS) on unaffected skin. Photoprovocation testing of the affected buttocks confirmed photosensitivity, with a positive UVA response on day 3. These findings align with BALPS. Therefore, photoinvestigations are useful for confirming BALPS, and both physical photoprotection and selective sunscreen are necessary for disease management.