Analyzing the effects of a chemical peel on post‐inflammatory hyperpigmentation using line‐field confocal optical coherence tomography

Dear Editor,

Line‐field confocal optical coherence tomography (LC‐OCT) is a burgeoning imaging device that allows for real‐time, high‐resolution, in vivo assessment of skin. ¹ , ² LC‐OCT utilizes a laser to measure the backscattering of light from cellular structures. ³ LC‐OCT can visualize up to 500 μm at quasi‐histological vertical (optical coherence tomography) and horizontal (reflectance confocal microscopy) views of the skin to produce a three‐dimensional image. In comparison to traditional confocal microscopy, LC‐OCT allows greater depth of visualization, and faster image acquisition. ¹ , ²

According to the 2020–2021 Aesthetic Plastic Surgery National Databank Statistics, chemical peels are one of the most extensively performed non‐invasive cosmetic procedures in the United States. ⁴ Chemical peels can be used to treat photoaging, lentigines, melasma, and post‐inflammatory hyperpigmentation. ⁵ Chemical peels cause controlled chemical injury leading to remodeling, regeneration, and wound healing. ⁶ We present a case study in which the patient presented to the clinic with complaints of hyperpigmented spots on his limb. To treat post‐inflammatory hyperpigmentation, the patient underwent two treatment sessions of targeted spot treatment using a commercially blended chemical peel containing trichloroacetic acid and lactic acid, with a 1‐month interval between sessions. LC‐OCT was utilized for imaging before and after completion of two treatment sessions. Images were acquired in a protocol to obtain vertical, horizontal, and 3D images. During the analysis of the images in vertical and horizontal views, the “deepmelanin” algorithm was used as it is the recommended algorithm for pigmented lesions. The algorithm was utilized to brighten melanin/pigmentation.

The analysis of pretreatment vertical images depicts hyperreflective pigmentation scattered through the epidermis. Post‐treatment vertical images show that pigmentation has shifted upwards in the epidermis. As a result, the upper layer of the epidermis appears brighter, and the lower epidermis displays reduced reflectivity (Figure 1). Furthermore, pre and post‐treatment horizontal (confocal) images of the epidermis were analyzed at the same depth. Pretreatment horizontal images demonstrate the presence of extensive areas of brightness indicating abnormal pigmentation. Conversely, post‐treatment horizontal images display a notable decrease in hyperreflective area, indicating a reduction in pigmentation at that specific depth (Figure 1). This reduction suggests that melanin has migrated upwards. This finding aligns with the results of our previous study that examined the effects of chemical peel on melanin using reflectance confocal microscopy. ⁸ In the current study, a 3‐dimensional (3D) projection mode was used in max reflective setting, to compare pre and post‐treatment. Hyper‐reflective parts of the image may represent a combination of pigmentation (melanin), pigmented cells (keratinocytes, melanocytes), and inflammatory cells. The pretreatment images show presence of hyperreflective pigmentation dispersed through epidermis, corresponding to greater melanin concentration. However, post‐treatment 3D projection images demonstrate an upward shift of pigmentation resulting in hyperreflective stratum corneum on the surface but a markedly reduced hyper reflectivity as we analyze deeper layers (Figure 2). On clinical examination, the hyperpigmented spots appeared lighter, fragmented, and less prominent after treatment sessions. The clinical findings align with the LC‐OCT findings in vertical, horizontal, and 3D modes.

FIGURE 1.

Vertical or optical coherence tomography view of LC‐OCT (1A) Pre‐treatment. (1B) One month after second treatment session. Horizontal or Confocal microscopy view of LC‐OCT. (2A) Pre‐treatment. (2B) One month after second treatment session.

FIGURE 2.

3‐Dimensional projection view (max reflectivity) of LC‐OCT. (A) Pre‐treatment. (B) 1 month after second treatment session.

Optical imaging devices, such as LC‐OCT, that allow in‐vivo subsurface evaluation of the skin have the potential to positively impact research in dermatology. These devices will enable clinicians to evaluate the effectiveness of cosmetic procedures and products with enhanced precision.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions