Fingernail Photo-onycholysis After Aminolevulinic Acid–Photodynamic Therapy Under Blue Light for Treatment of Actinic Keratoses on the Face

To the Editor:

Topical photodynamic therapy (PDT) is one of several effective treatments of actinic keratoses (AKs). Photodynamic therapy involves selection of a lesion field, application of a photosensitizer drug, incubation for an explicit period of time, and illumination of the area from a light source corresponding to the absorption spectrum of the chosen drug.¹ A photosensitizer drug used in PDT to target AK is aminolevulinic acid (ALA). Aminolevulinic acid converts disease tissue to photoactivatable porphyrins, especially protoporphyrin IX, which has its largest absorption peak (410 nm) in the blue spectrum, with smaller absorption peaks at 505, 540, 580, and 630 nm. Photodynamic therapy treatments historically have been carried out under red light (peak emissions, 630 nm) to improve tissue penetration, which is superior in efficacy when treating Bowen disease and basal cell carcinoma.^1,2 Broadband blue light (peak emission, 417 nm) now is routinely used and has been proven effective in combination with ALA for the treatment of AK.³ It was approved by the US Food and Drug Administration for AKs in 1999.⁴

Photo-onycholysis is a photosensitivity reaction defined as separation of the nail plate from the nail bed. There are 4 different types of photo-onycholysis characterized by appearance and by the number of digits affected: Type I is denoted by the involvement of several fingers, with half-moon–shaped separations of the nail plate. Type II affects a single finger and corresponds to a brown, defined, circular notch opening distally. Type III, which involves several fingers, is defined as round yellow stains in the central portion of the nail that turn red after 5 to 10 days. Type IV has been associated with bullae under the nails.⁵ There have been cases of photo-onycholysis arising after exposure to UV light following ingestion of certain prescription drugs or spontaneously,⁶ and a single case following PDT to the hands with red light.⁵ We report a case of fingernail photo-onycholysis resulting from ALA-PDT for the treatment of perioral AK.