Vessel diameter as a potential predictor of pulsed dye laser response in port wine stain: a retrospective exploratory reflectance confocal microscopy study.

To investigate whether noninvasive reflectance confocal microscopy (RCM)-derived vascular parameters can serve as objective predictors of therapeutic response to pulsed dye laser (PDL) treatment in patients with port wine stain (PWS), given the wide variability in clinical outcomes. We retrospectively reviewed the records of 240 patients with facial PWS who underwent RCM imaging before a scheduled PDL session, yielding their image datasets stratified by treatment history. The superficial vessel depth (SVD), maximum vessel diameter (MVD), and vessel density (VD) were quantified. Among 25 treatment-naïve patients with follow-up evaluations, treatment efficacy after a single PDL session was graded on a standardized quartile scale. Associations between RCM parameters and clinical outcomes were evaluated using nonparametric tests and Fisher's exact test, as appropriate. A longitudinal analysis was performed in 14 patients with available pre- and post-treatment RCM data. Vascular parameters differed significantly among groups stratified by prior PDL sessions. With increasing treatment sessions, SVD increased whereas MVD decreased significantly (both p < 0.05), while VD showed no significant difference. Among treatment-naïve patients, baseline MVD > 40 μm was associated with a significantly higher response rate than MVD ≤ 40 μm (p < 0.001). In the longitudinal subset, effective responders showed a significant post-treatment reduction in MVD, whereas ineffective responders did not. Baseline MVD assessed by RCM may serve as a potential imaging biomarker for predicting PDL response in patients with PWS. Larger vessels were associated with more favorable clinical improvement, while smaller vessels tended to show poorer response. These preliminary findings require validation in larger prospective cohorts before clinical implementation.