Photodynamic Therapy Performs Delayed Cumulative Response to the Treatment for Port-Wine Stains

Photodynamic therapy (PDT), an emerging treatment modality for port-wine stains (PWS) alongside pulsed dye laser (PDL) therapy, currently lacks clear guidelines regarding the optimal number of treatment sessions. In recent clinical practice, we found that for patients presented poor efficacy to initial PDT sessions, subsequent session exhibited significantly better efficacy than preceding ones. We termed this phenomenon "delayed cumulative response" (DCR). This study was to introduce and summarize the DCR for the first time, and to provide evidence for its existence, explore potential mechanisms. We conducted a retrospective study based on clinical data analysis of 80 PWS patients, comparing the efficacies between the session that performed DCR and the session before DCR, identifying influencing factors, and analyzing related pathological results. All lesions were located on the head, face, and neck. Patients typically experience DCR at the 2.79th ± 0.74th PDT session. The clearance rate of DCR session markedly increased from 21.71% in the previous session to 59.43%, while the VAS score rose from 1.27 to 2.75. Patients with PWS lesions involving single site were more prone to experiencing DCR. DCR phenomenon was observed in the PDT treatment of PWS. We defined DCR as a situation where the initial PDT sessions show limited efficacy (less than 25% improvement), followed by a subsequent session with significant efficacy (greater than 50% improvement). For patients with poor initial responses to PDT, we recommended scheduling at least 3 treatment sessions to achieve 60% clinical improvement.