The role of reflectance confocal microscopy in the diagnosis and management of pigmentary disorders: A review

BACKGROUND

Reflectance confocal microscopy (RCM) has quickly transitioned from a research tool to an adjunct diagnostic bedside tool, providing the opportunity for noninvasive evaluation of skin lesions with histologic resolution. RCM is an optical imaging technique that uses near-infrared excitation wavelengths and safe low-power lasers. En-face images of different skin layers (up to the superficial dermis) are acquired in grayscale based on the reflective indices of tissue components. Melanin has the highest reflective index (contrast) and appears bright on RCM.

AIMS

We present a review of the current literature on the use of RCM in the diagnosis and management of pigmentary disorders.

METHODS

We reviewed PubMed and Ovid Medline databases from January 2000 to June 2021, using MeSH key terms: "reflectance confocal microscopy, confocal laser scanning microscopy, pigmentary disorders, treatment, melasma, vitiligo, freckles, solar lentigo, lentigo, tattoo, complications, melanoma, skin cancers, pigmented lesions, post inflammatory, melanin, photoaging" to identify studies and review articles discussing the use of RCM in the diagnosis and management of pigmentary disorders.

RESULTS

RCM findings of pigmentary disorders were divided into the following categories: (1) disorders of increased pigmentation (post-inflammatory hyperpigmentation, melasma, Riehl's melanosis, solar lentigines, ephelides, hori nevus, naevus of Ota, café-au-lait macules, melanocytic nevus, melanoma, nevus spilus, labial mucosal melanosis, and mucosal melanoma), (2) disorders of decreased pigmentation or depigmentation (post-inflammatory hypopigmentation, vitiligo, nevus depigmentosus, halo nevus), and (3) exogenous pigmentation (tattoo, ochronosis).

CONCLUSION

RCM has been explored and proven valuable for the evaluation and management of pigmentary disorders including melasma, vitiligo, solar lentigines, tattoo, and tattoo-related complications.

Biopsy-free in vivo virtual histology of skin using deep learning

An invasive biopsy followed by histological staining is the benchmark for pathological diagnosis of skin tumors. The process is cumbersome and time-consuming, often leading to unnecessary biopsies and scars. Emerging noninvasive optical technologies such as reflectance confocal microscopy (RCM) can provide label-free, cellular-level resolution, in vivo images of skin without performing a biopsy. Although RCM is a useful diagnostic tool, it requires specialized training because the acquired images are grayscale, lack nuclear features, and are difficult to correlate with tissue pathology. Here, we present a deep learning-based framework that uses a convolutional neural network to rapidly transform in vivo RCM images of unstained skin into virtually-stained hematoxylin and eosin-like images with microscopic resolution, enabling visualization of the epidermis, dermal-epidermal junction, and superficial dermis layers. The network was trained under an adversarial learning scheme, which takes ex vivo RCM images of excised unstained/label-free tissue as inputs and uses the microscopic images of the same tissue labeled with acetic acid nuclear contrast staining as the ground truth. We show that this trained neural network can be used to rapidly perform virtual histology of in vivo, label-free RCM images of normal skin structure, basal cell carcinoma, and melanocytic nevi with pigmented melanocytes, demonstrating similar histological features to traditional histology from the same excised tissue. This application of deep learning-based virtual staining to noninvasive imaging technologies may permit more rapid diagnoses of malignant skin neoplasms and reduce invasive skin biopsies.

The first report of diagnosing of keratoacanthoma in Chinese Han patients using dermoscopy and reflectance confocal microscopy

BACKGROUND

Keratoacanthoma (KA) is a special kind of tumor, which is regarded as a variant of squamous cell carcinoma (SCC) in some academic disciplines. But differentiating KA from SCC remains a diagnostic challenge. The noninvasive techniques dermoscopy and reflectance confocal microscopy (RCM) can provide new insights for diagnosis.

OBJECTIVE

To observe the characteristics of KA under dermoscopy and reflectance confocal microscopy (RCM), in order to gain experience and reference for clinicians to facilitate earlier diagnosis.

METHODS

We collected two cases of KA, which were confirmed by clinical and histopathological examination. The two cases were examined by dermoscopy and RCM, respectively. Then, we collected the microscopic characteristics of KA lesions.

RESULTS

The dermoscopy features of KA are concentric circles of central crater, keratin mass, keratin scale, and polymorphic vascular pattern. The RCM features are described as refractile crust, atypical honeycomb pattern, dark center cells, large round nucleated cells, dendritic cells, and linear or round vessels traversing dermal papillae in the dermis.

CONCLUSION

KA has some specific dermoscopy and RCM features, which can provide a basis for doctors to diagnose and intervene earlier.

Reflectance confocal microscopy evaluation of pigmented lesions on tattooed skin

The evaluation of pigmented lesions on tattooed skin poses a diagnostic challenge for dermatologists, as a nevus may be partially or completely obscured by tattoo pigment. Because of incidences of melanoma arising from tattooed skin, the current gold standard is to biopsy these lesions. Reflectance confocal microscopy (RCM) is a noninvasive imaging modality used in the diagnosis and management of skin diseases that may allow for diagnosis, while preserving the tattoo design. Retrospective chart review was conducted to identify pigmented lesions on or near tattooed skin that were evaluated with RCM. Confocal characteristics and diagnoses were recorded and analyzed. Nineteen lesions from 15 patients were retrospectively reviewed. Tattoo pigment did not hinder evaluation and diagnosis of pigmented lesions on RCM. About 94.7% of lesions were diagnosed as benign melanocytic nevi by an expert confocal reader. One lesion was confocally diagnosed as melanocytic nevus with atypia but was found to be an inflamed melanocytic nevus on histology. Tattoo pigment particles were differentiated from other hyper-refractile entities by an expert confocal reader based on size, morphology, and clinical correlation. RCM may provide a solution to the diagnostic challenge of pigmented lesions on or near tattooed skin.

Reflectance confocal microscopy: Principles, basic terminology, clinical indications, limitations, and practical considerations

Reflectance confocal microscopy (RCM) is a noninvasive imaging tool used for in vivo visualization of the skin. It has been extensively studied for use in the evaluation of equivocal cutaneous neoplasms to decrease the number of biopsy procedures in patients with benign lesions. Furthermore, its applications are broadening to include presurgical cancer margin mapping, tumor recurrence surveillance, monitoring of ablative and noninvasive therapies, and stratification of inflammatory disorders. With the approval of category I Current Procedural Terminology reimbursement codes for RCM image acquisition and interpretation, use of this technology has been increasingly adopted by dermatologists. The first article in this 2-part continuing medical education series highlights basic terminology, principles, clinical applications, limitations, and practical considerations in the clinical use of RCM technology.