RESUMEN
INTRODUCTION: Photodynamic therapy (PDT) is a safe, non-mutagenic, and non-scarring treatment for actinic keratoses (AK). BACKGROUND: 'Painless' photodynamic therapy (p-PDT) is a regimen for AK that employs simultaneous aminolevulinate incubation and blue light illumination. The efficacy of p-PDT resembles that of traditional PDT, but detailed mechanisms of action for p-PDT are not well understood. METHODS: To characterize the inflammatory effects of the p-PDT procedure 48 h following treatment and determine the association of inflammation with precancer burden, we performed a retrospective cohort study of 104 patients with AK of face or scalp treated with p-PDT between 2017 and 2019. Patients self-reported their side effects 48 h following p-PDT and took photographs of their face and scalp. Photographs were edited to define seven anatomic regions, and erythema was scored by four investigators. RESULTS: Ninety-eight patients provided photographs suitable for erythema evaluation. Most patients experienced 2 or more side effects and some pain 48 h post-procedure. Females experienced more pain (p = 0.01) and side effects (p = 0.002) compared to males. AK burden was positively associated with post p-PDT erythema response (p < 0.0001) at all sites, but particularly in the temples (p = 0.002) and supralabial area (p = 0.009). DISCUSSION: This study confirms a strong clinical inflammatory response after p-PDT. Severity of inflammation is positively associated with AK tumor burden, suggesting that post-treatment inflammation may be a pre-requisite for p-PDT efficacy. Interestingly, the results also identify certain gender-related differences in the severity of side effects experienced by patients post-PDT.