BH14 Fibrosing alopecia in a patterned distribution following photodynamic therapy for actinic keratosis: a potential trigger for scarring alopecia

Abstract

Photodynamic therapy (PDT) is an established field treatment for actinic keratoses of the scalp. Expected adverse effects include pain, erythema, oedema and crusting, with occasional transient shedding. Permanent alopecia is rarely reported. Fibrosing alopecia in a patterned distribution (FAPD) is an uncommon lymphocytic cicatricial alopecia that combines features of female pattern hair loss (FPHL) and lichen planopilaris or frontal fibrosing alopecia. A 74-year-old woman with Fitzpatrick type II skin underwent scalp PDT for biopsy-proven moderate actinic keratosis. The treatment was complicated by an exaggerated inflammatory reaction with severe pain and pruritus, prolonged erythema and crusting, and secondary skin-swab-proven Staphylococcus aureus infection requiring oral antibiotics and topical corticosteroids. Within weeks she developed abrupt diffuse shedding and persistent loss of density without regrowth. She reported only mild gradual thinning beforehand. There were a 2-cm frontal hairline recession, midfrontal and vertex thinning (Sinclair grade 5) with patchy vertex involvement, perifollicular erythema and scale, and focal loss of follicular ostia. Blood tests were normal, including full blood count, ferritin, folate, vitamin B12, vitamin D, liver function tests and erythrocyte sedimentation rate. Paired horizontal and vertical biopsies showed follicular miniaturization consistent with FPHL together with perifollicular lamellar fibrosis, loss of sebaceous glands and a chronic lymphocytic infiltrate targeting the infundibulum and isthmus, supporting FAPD. The symptoms improved with clobetasol propionate scalp application, hydroxychloroquine and low-dose oral minoxidil, but hair density has not recovered. Published reports linking PDT to FAPD are lacking. This case supports the hypothesis that intense postprocedural inflammation may precipitate or accelerate FAPD in predisposed individuals. Persistent shedding after PDT should not be assumed to be telogen effluvium. Perifollicular inflammation or loss of ostia should prompt early trichoscopy, biopsy and anti-inflammatory treatment. Preprocedure counselling and a low threshold for ­follow-up may help limit irreversible hair loss in at-risk patients.