Differentiating solar lentigines from post‐inflammatory hyperpigmentation with hyperspectral imaging: A pilot study

Objective Solar lentigines and post‐inflammatory hyperpigmentation (PIH) are common pigmentation disorders, and they are usually differentiated by a trained dermatologist. Accurate identification of the spot type is essential for providing patients with the most appropriate skin treatment. The aim of this study was to evaluate the capacity of hyperspectral imaging (HSI) in characterizing and discriminating solar lentigines from PIH, that is, to identify the colorimetric features and chromophore concentrations associated with each pigmentation disorder. Methods Acquisition of HSI was performed using a liquid‐crystal tuneable filter spectral scanning spectrometer. The recruited panel consisted of female Japanese subjects ( n = 11) with one solar lentigo on both the left and right cheeks. Five of these subjects also had one PIH spot on both the left and right cheeks. Results Significant differences were found in the mean difference relative to the surrounding skin between PIH spots and solar lentigines for the following features (all p < 0.05): Δ Oxyhaemoglobin (PIH spots (2.3 ± 1.1) × 10 −2 g·cm·L −1 vs. solar lentigines (−0.1 ± 0.6) × 10 −2 g·cm·L −1 ), Δ Deoxyhaemoglobin (PIH spots (6.3 ± 2.6) × 10 −2 g·cm·L −1 vs. solar lentigines (0.9 ± 1.7) × 10 −2 g·cm·L −1 ), Δ a * values (PIH spots 5.3 ± 2.0 vs. solar lentigines 1.6 ± 1.3) and Δ b * values (PIH spots −1.2 ± 0.7 vs. solar lentigines −0.1 ± 0.4). No significant difference was observed in Δ L * values and Δ Melanin content between the two hyperpigmentation types (all p > 0.05). Conclusion Compared with solar lentigines, PIH spots displayed higher haemoglobin content and Δ a * values and lower Δ b * values. To strengthen these preliminary findings, further clinical studies need to be conducted on a larger cohort, aiming at confirming the benefit of HSI in accurately differentiating these two skin pigmentation disorders to support clinical assessment.