Progress and Prospect of Non-Invasive Detection Techniques in the Therapeutic Evaluation of Melasma
Melasma is a common, chronic, acquired, and refractory hyperpigmentation disorder with a multifactorial etiopathogenesis. Current treatments for melasma include topical or systemic agents, chemical peels, laser- and light-based therapies, and traditional Chinese medicine. However, evaluating the efficacy of these treatments remains a challenge. The therapeutic evaluation of melasma can be categorized into four main approaches: patient self-assessments, scoring systems used by dermatologists, non-invasive detection techniques, and histopathological and immunohistochemical assessments. Among these, non-invasive detection techniques have gained significant attention due to their ability to provide objective, reproducible, and trauma-free evaluations.
Skin Color Measurement Techniques
Skin color measurement techniques are essential for objectively assessing the severity of melasma and the efficacy of its treatment. These techniques are based on different principles and can be classified into four types: scanning reflectance spectrophotometers, tristimulus colorimeters, narrow-band reflectance spectrophotometers, and visible-spectrum reflectance colorimeters. Among these, three instruments have been widely used in clinical efficacy evaluations: the Chromameter, Mexameter, and Dermacatch.
The Chromameter is a tristimulus colorimeter that measures skin color based on the Lab color space, which quantifies lightness (L), redness (a), and yellowness (b). The Mexameter, on the other hand, uses narrow-band reflectance spectrophotometry to measure melanin and erythema indices. The Dermacatch is a visible-spectrum reflectance colorimeter that provides measurements of skin color and pigmentation.
Some researchers have combined these instruments to achieve more objective assessments. For example, the Chromameter has been used in conjunction with the Mexameter to evaluate the efficacy of fractional Q-switched 1064-nm neodymium-doped yttrium aluminum garnet (Nd:YAG) laser treatment in melasma patients. Similarly, the Mexameter has been paired with the Dermacatch to assess the efficacy of cysteamine cream in treating epidermal melasma.
Skin Imaging Techniques
Skin imaging techniques encompass a variety of technologies based on laser, ultrasound, and electromagnetic waves. These techniques have been widely used in the diagnosis, classification, severity assessment, and therapeutic evaluation of melasma. The most commonly used skin imaging techniques in melasma research include ultraviolet optical imaging, VISIA, Antera 3D, dermoscopy, and reflectance confocal microscopy (RCM).
Ultraviolet Optical Imaging and Quantitative Analysis Technology
Ultraviolet (UV) optical imaging is a technique that utilizes UV light to objectively quantify the severity of pigmentary skin diseases, particularly melasma. Onseok et al. developed an air cooling scientific complementary metal-oxide-semiconductor (sCMOS) charge-coupled device (CCD) camera to acquire images of areas prone to melasma. The gradient mask algorithm was used to segment the target images in the region of interest (ROI) and correct facial curvature. The authors developed a quantitative evaluation method by calculating the arithmetic mean of the gray level and the coefficient of variation per pixel of the normal area and pigment lesion area under UV conditions. Additionally, the red, green, and blue (RGB) color model was converted to the Lab color model in normal and pigment lesion areas under visible light conditions, and Lab and DE values were used for further analysis.
VISIA
VISIA is a complexion analysis system that evaluates the skin phototype and eight parameters, including spots, wrinkles, texture, pores, UV spots, brown spots, red areas, and porphyrins on the forehead and both cheeks. Feng et al. calculated the correlation between the melasma area and severity index (MASI) score and the VISIA analysis. They found that the eigenvalues and scores for spots, red areas, and brown spots were positively associated with the MASI score, indicating that VISIA can be a useful tool for assessing the severity of melasma.
Antera 3D
Antera 3D uses reflectance mapping of seven different light wavelengths spanning the entire visible spectrum to map the distribution and concentration of melanin and hemoglobin. Ana et al. compared the Antera 3D with the Mexameter MX-18 and the Colorimeter CL-400 and found that the Antera 3D had better sensitivity and specificity than the Mexameter MX-18 regarding the melanin parameter. Additionally, the Antera 3D showed good correlations for all the parameters analyzed and had higher repeatability, making it a valuable tool for evaluating melasma treatment efficacy.
Dermoscopy
Dermoscopy allows for the visualization of melanin color intensity, pigment network regularity, and the density and localization of melanin. It also provides information on changes in blood vessels in a timely and dynamic manner. Naglaa et al. performed evaluations using the modified MASI (mMASI) and dermoscopy. The dermoscopic examination showed a decrease in the density of pigmentation and the severity of skin telangiectasia after treatment and at follow-up, highlighting the utility of dermoscopy in monitoring treatment progress.
Reflectance Confocal Microscopy (RCM)
RCM is a non-invasive imaging technique that correlates well with dermoscopy and can be used to observe the structure of the entire epidermis and the superficial layer of the dermis. It provides detailed information on pigment distribution, blood vessel size, and superficial location. RCM has a resolution that reaches the cellular level and correlates well with histopathological manifestations.
Ardigo et al. performed a semi-quantitative assessment of the degree of pigmentation in different skin layers in melasma patients using RCM. Hee et al. scored parameters such as epidermal pigmentation, dendritic cells or melanophages, and solar elastosis to quantify changes in melasma. They found that the distribution of melanophages in melasma was not homogeneous, and counting vessels was difficult, but RCM provided valuable insights into the structural changes associated with melasma.
Combined Applications
Combining multiple skin imaging techniques can provide a more comprehensive evaluation of melasma treatment efficacy. Huang et al. used RCM to evaluate the quantity and distribution of melanin and observe the morphology of melanin and dendritic melanocytes. Dermoscopy was performed to assess the quantity and morphology of blood vessels. The authors concluded that assessing morphological changes in melanin made the evaluation results more objective and specific, and the observation through dermoscopy could offset the difficulty with RCM in counting blood vessels.
Some researchers have simultaneously applied several skin imaging techniques to evaluate efficacy more objectively. For example, VISIA has been combined with Antera 3D, and RCM has been used in conjunction with VISIA and dermoscopy to provide a more detailed and accurate assessment of melasma treatment outcomes.
Conclusions
The treatment of melasma remains a challenge for dermatologists due to its multifactorial pathogenesis and high recurrence rate. While there are numerous methods to evaluate the efficacy of melasma treatment, non-invasive detection techniques have become the focus of many researchers due to their ability to provide objective, reproducible, and trauma-free evaluations.
Skin color measurement techniques, such as the Chromameter, Mexameter, and Dermacatch, have been widely used in clinical efficacy evaluations. Combining these instruments can improve the objectivity of assessments. Skin imaging techniques, including UV optical imaging, VISIA, Antera 3D, dermoscopy, and RCM, have also been extensively applied in the diagnosis, classification, severity assessment, and therapeutic evaluation of melasma.
These techniques offer unique advantages, such as the ability to quantify pigmentary changes, observe structural changes at the cellular level, and monitor treatment progress in real-time. Combining multiple skin imaging techniques can provide a more comprehensive evaluation of melasma treatment efficacy, addressing the limitations of individual methods.
Future research into the non-invasive detection and therapeutic evaluation of melasma should focus on further developing and refining these techniques to improve their accuracy, sensitivity, and specificity. Additionally, studies should explore the correlations between non-invasive imaging findings and histopathological changes to better understand the underlying mechanisms of melasma and optimize treatment strategies.
doi.org/10.1097/CM9.0000000000000984
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