Traditionally, diagnosis of skin disease relies on clinical inspection, often followed by biopsy and histopathologic examination. In recent years, new noninvasive tools have emerged that can aid in clinical diagnosis and reduce the number of unnecessary benign biopsies. Although there has been a surge in noninvasive diagnostic technologies, many tools are still in research and development phases, with few tools widely adopted and used in regular clinical practice. In this article, we discuss the use of dermoscopy, reflectance confocal microscopy (RCM), and optical coherence tomography (OCT) in the diagnosis and management of skin disease.
Dermoscopy
Dermoscopy, also known as epiluminescence light microscopy and previously known as dermatoscopy, utilizes a ×10 to ×100 microscope objective with a light source to magnify and visualize structures present below the skin’s surface, such as melanin and blood vessels. There are 3 types of dermoscopy: conventional nonpolarized dermoscopy, polarized contact dermoscopy, and nonpolarized contact dermoscopy (Figure 1). Traditional nonpolarized dermoscopy requires a liquid medium and direct contact with the skin, and it relies on light reflection and refraction properties.1 Cross-polarized light sources allow visualization of deeper structures, either with or without a liquid medium and contact with the skin surface. Although there is overall concurrence among the different types of dermoscopy, subtle differences in the appearance of color, features, and structure are present.1
Figure 1. A, Melanocytic nevus using nonpolarized contact dermoscopy. B, Melanocytic nevus using polarized contact dermoscopy. C, In situ malignant melanoma using nonpolarized contact dermoscopy. D, In situ malignant melanoma using polarized contact dermoscopy.
Dermoscopy offers many benefits for dermatologists and other providers. It can be used to aid in the diagnosis of cutaneous neoplasms and other skin diseases. Numerous low-cost dermatoscopes currently are commercially available. The handheld, easily transportable nature of dermatoscopes have resulted in widespread practice integration. Approximately 84% of attending dermatologists in US academic settings reported using dermoscopy, and many refer to the dermatoscope as “the dermatologist’s stethoscope.”2 In addition, 6% to 15% of other US providers, including family physicians, internal medicine physicians, and plastic surgeons, have reported using dermoscopy in their clinical practices. Limitations of dermoscopy include visualization of the skin surface only and not deeper structures within the tissue, the need for training for adequate interpretation of dermoscopic images, and lack of reimbursement for dermoscopic examination.3
Many dermoscopic structures that correspond well with histopathology have been described. Dermoscopy has a sensitivity of 79% to 96% and specificity of 69% to 99% in the diagnosis of melanoma.4 There is variable data on the specificity of dermoscopy in the diagnosis of melanoma, with one meta-analysis finding no statistically significant difference in specificity compared to naked eye examination,5 while other studies report increased specificity and subsequent reduction in biopsy of benign lesions.6,7 Dermoscopy also can aid in the diagnosis of keratinocytic neoplasms, and dermoscopy also results in a sensitivity of 78.6% to 100% and a specificity of 53.8% to 100% in the diagnosis of basal cell carcinoma (BCC).8 Limitations of dermoscopy include false-positive diagnoses, commonly seborrheic keratoses and nevi, resulting in unnecessary biopsies, as well as false-negative diagnoses, commonly amelanotic and nevoid melanoma, resulting in delays in skin cancer diagnosis and resultant poor outcomes.9 Dermoscopy also is used to aid in the diagnosis of inflammatory and infectious skin diseases, as well as scalp, hair, and nail disorders.10
Reflectance Confocal Microscopy
Reflectance confocal microscopy utilizes an 830-nm laser to capture horizontal en face images of the skin with high resolution. Different structures of the skin have varying indices of refraction: keratin, melanin, and collagen appear bright white, while other components appear dark, generating black-and-white RCM images.11 Currently, there are 2 reflectance confocal microscopes that are commercially available in the United States. The Vivascope 1500 (Caliber ID) is the traditional model that captures 8×8-mm images, and the Vivascope 3000 (Caliber ID) is a smaller handheld model that captures 0.5×0.5-mm images. The traditional model provides the advantages of higher-resolution images and the ability to capture larger surface areas but is best suited to image flat areas of skin to which a square window can be adhered. The handheld model allows improved contact with the varying topography of skin; does not require an adhesive window; and can be used to image cartilaginous, mucosal, and sensitive surfaces. However, it can be difficult to correlate individual images captured by the handheld RCM with the location relative to the lesion, as it is exquisitely sensitive to motion and also is operator dependent. Although complex algorithms are under development to stitch individual images to provide better correlation with the geography of the lesion, such programs are not yet widely available.12
Reflectance confocal microscopy affords many benefits for patients and providers. It is noninvasive and painless and is capable of imaging in vivo live skin as compared to clinical examination and dermoscopy, which only allow for visualization of the skin’s surface. Reflectance confocal microscopy also is time efficient, as imaging of a single lesion can be completed in 10 to 15 minutes. This technology generates high-resolution images, and RCM diagnosis has consistently demonstrated high sensitivity and specificity when compared to histopathology.13 Additionally, RCM imaging can spare biopsy and resultant scarring on cosmetically sensitive areas. Recently, RCM imaging of the skin has been granted Category I Current Procedural Terminology reimbursement codes that allow provider reimbursement and integration of RCM into daily practice14; however, private insurance coverage in the United States is variable. Limitations of RCM include a maximum depth of 200 to 300 µm, high cost to procure a reflectance confocal microscope, and the need for considerable training and practice to accurately interpret grayscale en face images.15