Longitudinal Imaging Patterns Following an Imaging-Guided Dual-Axis Picosecond Nd

BACKGROUNDFacial hyperpigmentation is commonly treated with pigment-directed laser procedures and repeated low-fluence toning. Although effective in many patients, these approaches may be followed by post-inflammatory hyperpigmentation (PIH), recurrence after initial improvement, or therapeutic plateaus that limit further pigment clearance.

OBJECTIVESTo characterize longitudinal multimodal imaging patterns following an imaging-guided dual-axis picosecond Nd:YAG protocol and to determine whether changes in pigment-associated measures were accompanied by changes in polarized-light (PL) imaging.

METHODSThis retrospective, nonrandomized, hypothesis-generating study included 53 patients with persistent or recurrent facial hyperpigmentation characterized by coexisting epidermal-predominant and dermal-predominant pigmentary components on multimodal imaging. The dual-axis protocol group (n = 15) received selective 532-nm irradiation of epidermal-predominant pigmentation and repeated 1064-nm irradiation of dermal-predominant or mixed lesions, with the 1064-nm component calibrated primarily according to transient focal erythema within a clinically acceptable sub-purpuric range. The retrospectively identified conventional-treatment group (n = 38) received heterogeneous multimodal laser treatments reflecting routine clinical practice. Standardized lesion-centered regions of interest were analyzed at baseline, Session 5, and Session 9 using normal-light, ultraviolet (UV), and PL imaging. Outcomes included the Melanin Index (MI), UV index, and PL index.

RESULTSAt Sessions 5 and 9, the dual-axis protocol group showed greater reductions in MI, UV index, and PL index than the conventional-treatment group. At Session 9, median percentage reductions were 43.7% for MI, 40.6% for UV index, and 18.0% for PL index in the dual-axis protocol group, compared with 9.1%, 8.0%, and 2.6%, respectively, in the conventional-treatment group. Baseline-adjusted differences were significant for all three indices (all p < 0.001). Complete-case analysis, sensitivity analysis addressing baseline UV imbalance, and single-index responder analyses yielded directionally consistent findings. In 15 selected cases, two manual intra-observer reassessments showed directional concordance of 94.4% and 96.7% with the original analysis.

CONCLUSIONSThe dual-axis protocol was associated with coordinated longitudinal reductions across pigment- and PL-associated imaging domains. These exploratory findings provide a rationale for prospectively evaluating whether multimodal imaging, including normal-light, UV, and PL imaging, can assist treatment-target selection, serial reassessment, and response-calibrated treatment. They do not establish clinical utility, vascular–melanocytic decoupling, or causal treatment superiority and require validation in prospective controlled studies.

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