Efficacy, Safety, and Predictive Value of Quantitative Histopathology in Picosecond Laser Therapy for Congenital Melanocytic Nevi

In this single-arm prospective study, we evaluated the efficacy and safety of a 1064/532-nm Nd:YAG picosecond laser for congenital melanocytic nevi (CMN) and investigated the association between clinical response and quantitative histopathologic findings. Thirteen Japanese patients with a median age of 4 years were enrolled and received up to five laser treatment sessions at 1- to 3-month intervals. Clinical efficacy was primarily assessed using the Investigator Global Assessment (IGA) score at 3 months after treatment, supplemented by Melanin Index analysis and ImageJ-based histopathologic quantification of nevus cell area fraction and melanin distribution. At the 3-month follow-up, 30.8% of patients achieved an IGA score of 5 (≥ 75% improvement), and 84.6% achieved an IGA score of 4 (50%-74% improvement) or higher. The Melanin Index decreased significantly (p < 0.001); at 1 year, the group-level mean remained significantly below baseline, although 3 of 13 patients had values above baseline. Histopathologic analysis showed a strong negative correlation between IGA score and nevus cell area fraction (ρ = -0.849, p = 0.0002). In an exploratory multivariable analysis, nevus cell area fraction remained significantly associated with clinical outcome, whereas peak cumulative mean melanin area fraction was not. All participants experienced transient local treatment-related adverse events; however, these resolved by the 3-month follow-up without treatment discontinuation or irreversible sequelae. These findings suggest that picosecond laser therapy may be a safe and effective minimally invasive treatment option for CMN and that clinical responsiveness may be more closely associated with nevus cell burden than with the depth-related melanin distribution parameter. Pretreatment histopathologic evaluation of nevus cell area fraction may therefore be useful for predicting clinical response.

Abstract from PubMed