Isolated Actinic Prurigo Cheilitis in an Elderly Thai Female: An Atypical Presentation.

Actinic prurigo (AP) is a rare photodermatosis with variable clinical presentations across different ethnic populations. While lip involvement is common in Latin American populations, isolated cheilitis as the sole manifestation in elderly Asian patients has not been previously documented. We report a 67-year-old Thai female presenting with chronic, recurrent painful ulcers on the lower lip persisting for six months. Despite multiple treatments at a private clinic, new lesions continued to develop. Dermatological examination revealed multiple erosions on an erythematous, edematous plaque at the vermilion border of the lower lip. Histopathological examination demonstrated dense lymphocytic infiltration with well-defined lymphoid follicles, demonstrating the histopathological pattern of follicular cheilitis, which is pathognomonic for actinic prurigo cheilitis. Interestingly, phototesting and photoprovocation yielded normal results across all UV spectra. Complete remission was achieved after two months of treatment with topical 1.25% hydrocortisone cream combined with strict sun protection measures. This case highlights an unusual phenotype of actinic prurigo in an Asian patient, characterized by isolated lip involvement in the absence of other cutaneous manifestations. It underscores the importance of considering AP in the differential diagnosis of chronic lip lesions, even in atypical demographics and with normal phototesting results. The favorable response to conservative management emphasizes the value of early recognition and appropriate treatment.