A Study on Applying Slide-Free Label-Free Harmonic Generation Microscopy For Noninvasive Assessment of Melasma Treatments With Histopathological Parameters

Abstract

Melasma, which is thought to be associated with hyperactivation of melanocytes, is a common hyperpigmentary skin disorder. To treat this skin disorder, dermatologists can benefit from in vivo information of cellular morphometrics to evaluate pathologies of melasma and effectiveness of treatments. To acquire this useful information, we applied the in vivo slidefree label-free harmonic generation microscopy (HGM) to retrieve real-time HGM images and subsequent critical histopathological parameters. These in vivo quantitative parameters included melanin mass density (MMD), melanocyte dendricity score (MDS), melanophage density (MPD), and thickness of dermal papilla zone (DPZ). The statistical results from 33 recruited Asian female melasma patients showed that MMD, MDS, and MPD in melasma lesions were significantly higher than those in the surrounding normal skin; by contrast, the DPZ was lower. After treatment, the MMD, MPD, and DPZ restored toward the normal level; however, we observed no significant change of MDS. Our study indicates that these parameters are able to serve as clinical indices to evaluate the histopathological characteristics of melasma patients and the effectiveness of treatments.

A longitudinal comparative study by in vivo harmonic generation microscopy: Q‐switched ruby laser versus picosecond 532‐nm Nd: YAG laser for the treatment of solar lentigines

“…29 Consistent with the findings, we previously successfully demonstrated that melanocyte dendricity was significantly higher in melasma than that in the surrounding normal skin by in vivo HGM imaging. 30 However, the EMDS of SLs was not higher than the perilesional normal skin in our study which is consistent with the in vivo reflectance confocal microscopy (RCM) study performed by Richtig et al 31 The reason may be due to the high background signals from melanin enhancement in basal keratinocytes of SLs, which interferes with the observation of mild elongation of melanocytic dendrites. Contrary to the previous RCM study which showed no activated melanocytes 10 days after QSRL treatment for SLs, 31 we observed significantly increased EMDS 3-6 weeks after both QSRL and PSNYL treatments.…”

“…Increased melanocyte dendricity has been demonstrated by double immunostaining of c‐kit and MITF in SLs, melasma and acne‐induced PIH 29 . Consistent with the findings, we previously successfully demonstrated that melanocyte dendricity was significantly higher in melasma than that in the surrounding normal skin by in vivo HGM imaging 30 . However, the EMDS of SLs was not higher than the perilesional normal skin in our study which is consistent with the in vivo reflectance confocal microscopy (RCM) study performed by Richtig et al 31 The reason may be due to the high background signals from melanin enhancement in basal keratinocytes of SLs, which interferes with the observation of mild elongation of melanocytic dendrites.…”

A Noninvasive Skin Biopsy of Free Nerve Endings via Realtime Third-Harmonic Microscopy

“…Our previous study confirmed that 1260 nm based epi-THG microscopy is not sensitive to dendrites of Langerhans cells [55]. Since THG is also sensitive to melanocyte dendrites, it is thus advised to choose skin areas with minimized melanocyte activities [56] and to use morphological characteristics to avoid the misdiagnosis of melanocyte dendrites as nerves.…”

“…Since THG is also sensitive to melanocyte dendrites, it is thus advised to choose skin areas with minimized melanocyte activities [56] and to use morphological characteristics to avoid the misdiagnosis of melanocyte dendrites as nerves. The melanocyte dendrites, an indication of hyperactivity of melanocytes, generally appeared on pigmented skin lesions, melanocyte tumors, and the skin after laser therapy rather than in normal skin [56].…”

In vivo microscopy as an adjunctive tool to guide detection, diagnosis, and treatment

“…Furthermore, longitudinal IVM may be used to monitor response to various therapies without biopsy, such as endoscopic mucosal or radiofrequency (RF) ablation, photodynamic therapy, skin pigmentation disorder treatments, and others. 34 – 37 …”