Fibrosing Alopecia in a Patterned Distribution Following Photodynamic Therapy for Actinic Keratosis: A Potential Trigger for Scarring Alopecia

Photodynamic therapy (PDT) for actinic keratosis can lead to unexpected permanent alopecia, as demonstrated in a case involving a 74-year-old woman who developed fibrosing alopecia in a patterned distribution (FAPD) following treatment. This condition, which combines features of female pattern hair loss and lichen planopilaris, was triggered by an exaggerated inflammatory reaction post-PDT, resulting in severe pain, pruritus, and a Staphylococcus aureus infection. Despite treatment with clobetasol propionate, hydroxychloroquine, and low-dose oral minoxidil, hair density did not recover. The case suggests that intense inflammation post-PDT may precipitate or accelerate FAPD in predisposed individuals, highlighting the need for early intervention and careful preprocedure counselling to prevent irreversible hair loss.