Cutaneous diagnosis is often, but not always, visually based. Dermatologists tend to encounter situations where the possibility of multiple differentials complicates the diagnosis and mandates investigations for confirmation. Methods commonly employed for cutaneous diagnosis may be invasive (skin and scalp biopsy), semi-invasive (slit skin smears, trichogram, etc.) or non-invasive (e.g., KOH smear, nail clipping, hair count for hair loss). Dermoscopy, also known as epiluminescence microscopy or skin surface microscopy is a non-invasive, in-vivo technique, which has traditionally found use in the evaluation and differentiation of suspicious melanocytic lesions from dysplasia and melanomas, and non-melanoma skin cancers [NMSCs] such as basal cell carcinoma (BCC).
However, over the last several years, the use of dermoscopy has been increasing in the context of general dermatological disorders like inflammatory dermatosis, pigmentary dermatosis, infectious dermatosis, disorders of hair and scalp, and nail. Some terms are used to describe specific indications: pigmentaroscopy, trichoscopy (dermoscopy of scalp and hair), onychoscopy (nails), inflammoscopy (inflammatory dermatosis), entomodermoscopy (skin infestations and infections). The role of dermoscopy in diagnosing disorders of general dermatology has undergone elaborate discussion. In this chapter, we shall review the plethora of extra-diagnostic indications of this technique and dwell upon the technical aspects worth considering.
A dermatoscope functionally simulates a magnifying lens, with the added features of much higher magnification, and an adjustable inbuilt illuminating system. A hand-lens even with in-built illumination, can not see beyond the surface of the skin because of the reflection and scattering of light from the stratum corneum. A dermatoscope can assess structures till the depth of reticular dermis and record images for future comparison. The basic principle of dermoscopy is transillumination of a lesion and studying it with high magnification to visualize subtle features. Light incident on a surface like the skin, may get reflected, refracted, diffracted and/or absorbed [Figure 1A]. The physical properties of the skin influence these phenomena. Most of the light incident on dry, scaly skin is reflected, but smooth, oily skin allows most of the light to pass through it, reaching the deeper dermis. By applying a linkage or immersion fluid (like mineral oil, liquid paraffin, ultrasound gel, or 70% alcohol-based commercial solutions) over the skin, its translucency is enhanced improving the visibility of the subsurface skin structures of the lesion under investigation. The essential components of a dermatoscope include 1) a set of achromatic lenses with magnification starting from 10× up to 200× or even higher, 2) an inbuilt illuminating system composed of halogen lamps placed within the handheld piece, 3) a source of power supply such as rechargeable or replaceable batteries or rechargeable handles.
The new generation of dermatoscopes come with inbuilt crossed-polarizers, which filter out the scattered light from the periphery, reduce the glare, and permit visualization of the substratal structures without the need of a linkage fluid. Figure 1B demonstrates the basic working of the modern dermatoscopes schematically. For taking and storing images, some dermatoscopes have an inbuilt photography system with supporting software for the capture and storage of images. For those dermatoscopes which do not have an inbuilt system, special adapters are available to connect to digital cameras. Advanced devices have whole body mapping systems for detailed analysis and follow up of skin lesions. Newer handheld units can attach to smart-phones for easier image capture and documentation.
Dermatoscopes and the technique utilized classify in various ways. A dermatoscope may be with or without an in-built image capturing facility. A simple hand-held dermatoscope looks like a broader version of an otoscope and lacks an inbuilt camera. Image-capture dermatoscopes have a special lens, which mounts onto a conventional or a digital camera. A united serial bus (USB) video-dermatoscope has a high-resolution camera fitted to the handpiece that allows visualization of the image on the computer screen as well as capturing videos. Advanced dermatoscopes have an analytical capability in addition to image-capture.
Dermoscopy is performable by either the non-contact or the contact technique. In the contact technique, the glass plate of the instrument touches the lesion through the linkage fluid. In the non-contact technique, the cross-polarized lens absorbs all the scattered light and hence allows only light in a single plane to pass through it without contact of the lens with the skin. The contact technique gives better illumination and resolution. The advantage of the non-contact technique is the prevention of inter-patient infections. Avoidance of cross-infection in the case of contact dermoscopy is by using a barrier like a cling film or adhesive tape over the lesional skin.
Although the advent of high-quality dermatoscopes with a polarizer has rendered the use of linkage fluids and contact dermoscopy almost redundant; it is worthwhile to be cognizant of the concept. The linkage fluid enhances the translucency of stratum corneum facilitating imaging of deeper structures. Many substances can function in this capacity including mineral oil, ethanol, liquid paraffin, and ECG/USG gel. The latter remains the most commonly used linkage fluid in the current era, especially for onychoscopy.
The recent improvements in the manufacturing of dermatoscopes include - reduction in dimensions and bulk of the device, wi-fi connectivity for USB dermatoscopes, digital image analysis, and attempts to incorporate artificial intelligence to create an automated diagnostic unit.
As a non-invasive technique, dermoscopy is essentially free of complications. The only issue is the minimal possibility of cross-infection between patients, especially with contact dermoscopy. Many tricks can obviate the possibility of cross-infection:
1) Use of polarized non-contact dermoscopy
2) Disinfection of the lens (in case of contact dermoscopy) or the rim of the USB video-dermatoscope with isopropyl alcohol after examining each patient
3) Use of disposable transparent lens shielding material like a cling film or soft plastic caps over the device; the latter are now being provided complimentary with most of the high-quality dermatoscopes - for use in both hand-held and USB video-dermatoscopes.
Minor issues worth consideration
1) One should be aware of artifacts of dermoscopy that may suffer from incorrect interpretation. Common artifacts include vermillion powder, colored powders, dust particles, hair dye, henna, hair fibers minoxidil crystals, hair styling gel, etc. in trichoscopy, dust particles, topical applications especially sunscreen and make-up ingredients during dermoscopy of the face, and nail paint and varnish in onychoscopy. The area to be scoped should be thoroughly cleaned with alcohol first to remove these artifacts.
2) The inter-device color difference in images - Different dermatoscopes tend to give images with a mildly skewed color balance. One must be aware of that and interpret results accordingly
3) The difference in different skin types - It is now amply clear that many features that are easy to appreciate in white skin, are either not seen/obscured in darker skin types. Honeycombing in the scalp is considered suggestive of androgenetic alopecia (AGA) in Fitzpatrick skin phototypes 1 to 3 but is a normal finding in the scalp of individuals with darker skin types. The colors (black, brown, gray, and blue) that have their basis in the histological level are neither easy to observe nor interpret in dark skin. Brown pigmented structures are often seen on dermoscopy of various disorders in ethnic skin due to the propensity of post-inflammatory hyperpigmentation, and thus warrant careful interpretation.
4) Lack of 'dermoscopic nomograms': To master the interpretation of histopathology, one must be thoroughly conversant with the normal histology, taking into account expected physiological variations due to a particular part of the human body, age, and gender. For example, the normal mucoscopic images from buccal mucosa reveal plentiful vessels, which should not be confused as a pathological feature. There is an urgent need to have an image bank of such site-specific, and skin type-specific dermoscopic nomograms to minimize errors in the interpretation of dermoscopic structures.
Dermoscopy may result in confirmation of clinical diagnosis, often avoiding the need for a skin biopsy. Although a skin biopsy and clinicopathological correlation (CPC) remain the gold standard for cutaneous diagnosis, dermoscopy often helps tilt the clinical differential in instances where it identifies a distinct pattern. Its use has been most popular for differentiation between melanocytic nevi and melanomas in the West. However, the indications of dermoscopy are continually expanding and include an evaluation of hair disorders, general pigmentary disorders, appendageal tumors, inflammatory disorders like psoriasis and lichen planus, and for pre- and post-evaluation of therapeutic procedures. In the current scheme of things, we are gradually moving from CPC to clinico-dermoscopic-pathological correlation (CDPC).
Dermoscopic patterns (mainly based on pigment and vascular patterns) for conditions like melanoma and NMSCs have been well established, leading to the development of dermoscopic algorithms for early diagnosis and triage. Documentation of dermoscopy patterns for general dermatological conditions, other than tumors, has also improved significantly over the past few years. Work is also being done to establish differences in these patterns, especially in patients with a skin of color (SOC).
Uses of dermoscopy beyond diagnosis
The dermatoscope is an immensely versatile tool, with many more uses beyond diagnosis. Its uses beyond diagnosis include:
Disease activity evaluation: Dermoscopy can confidently predict disease activity, e.g., active alopecia areata (AA) shows black dots, 'exclamation-mark' hairs, broken hairs, yellow dots and clustered short vellus hairs, whereas, in a treatment-responsive patch of AA, black dots tend to disappear, pig-tail, and upright regrowing hairs appear and yellow dots persist. Dermoscopy has similarly been found useful for assessing vitiligo stability, which is an essential criterion for surgical intervention. In our observation, perifollicular depigmentation (PFD), marginal hyperpigmentation, and presence of leucotrichia are suggestive of lesional stability, while an altered pigment pattern, perifollicular pigment retention (PFP), and features such as star-burst appearance, comet tail sign, and ‘tapioca sago’ appearance are suggestive of disease activity. Presence of background erythema is suggestive of disease activity in frontal fibrosing alopecia (FFA). Dermoscopic features have also been reported to predict the presence of residual disease [residual disease-associated dermoscopic criteria (RDADC)] in skin tumors such as BCC.
Early comparison of pre- and post-treatment: Appreciation of the post-treatment effect often precedes clinical improvement; this is especially true of chronic relapsing, recalcitrant dermatoses like melasma, lichen planus pigmentosus (LPP), vitiligo, alopecias, etc. The dermoscopic images not only offer confidence to the treating dermatologist about the appropriateness of the therapeutic protocol; they provide reassurance to the patient about the effectiveness of the treatment and increase patient compliance.
Ex-Vivo Dermoscopy (EVD) to improve histopathological evaluation: Dermoscopy-guided histological sectioning of the biopsy tissue can improve upon the sectioning of melanocytic neoplasms. Combining EVD with derm-dotting (DD) in which a dermoscopically suspicious area of the biopsy specimen gets marked with nail varnish has been reported to allow more accurate and less time-consuming histopathologic diagnosis of skin tumors.
Better doctor-patient communication: Dermoscopy improves the doctor-patient communication regarding all aspects of skin disease. Explaining the nature of the disorder becomes easier by patients showing the lesional dermoscopic image to the patient. Patients who warrant a skin biopsy but refuse to get it almost always consent for the same after having been shown the dermoscopic image a concept popular as 'dermoscopy-induced biopsy.' Dermoscopy also aids in the selection of the optimum site for biopsy. Dermoscopy-guided skin biopsy is useful in various pigmentary disorders, scalp conditions, vasculitis, and skin tumours.
Dermoscopic images as an evolving tool for clinical studies:
Since dermoscopy has proven a role as an early, objective and reliable measure of pre- and post-treatment comparison, it is now increasingly being used as an adjuvant tool for efficacy evaluation of therapeutic modalities in clinical studies. Gaining more experience and evidence of dermoscopy as the marker of therapeutic outcome may eventually obviate the need for repeat biopsy for response evaluation, rendering the study less and less invasive.
Dermoscopy in Dermatosurgery & Aesthetics: Dermoscopy has been reported to facilitate the prompt identification and removal of retained sutures in crusted wounds. Dermoscopy can also facilitate the identification and removal of a foreign body impacted in the skin. Dermoscopy also finds its utility in certain cosmetic/aesthetic procedures, e.g., the dermoscopic photoaging scale (DPAS), has been recently conceived and validated for quantitative evaluation of photoaged facial skin.
Dermoscopic evaluation of peri-ocular hyperpigmentation can aid in identifying the predominant abnormality (skin pigmentation, abnormal vasculature, skin laxity) thereby help in the development of customized treatment protocol.
Dermoscopy plays a significant role in optimizing the outcome of laser hair reduction (LHR) and has been reported to be useful in monitoring the response to LHR in women. Evaluation of the scattering and thickness of hairs before laser session has been especially utile in dark-skinned patients with hirsutism. Laser parameters, especially pulse duration (that depends on the thickness of the hair being targeted) can be fine-tuned.
Hair transplant surgeons are increasingly using trichoscopy. It allows recording of the number of existing follicular units, the number of hair per follicular unit, the size of hair follicles, and other parameters at the donor and recipient sites. Trichoscopy aids in early differential diagnosis of post-transplant complications such as folliculitis and secondary lichen planopilaris. It is also useful in optimizing outcome of ancillary trichology procedures such as scalp micro pigmentation (SMP).
Dermoscopy has been reported to aid in confirmation of pathergy test in patients with Behcet’s disease. On similar principles, dermoscopic imaging can aid in confirmation of a patch test reaction being a true positive or irritant, especially in dark-skinned individuals. Dermoscopy has also proved useful in mapping and better ablation of 'cosmetic warts,' especially verruca plana in the shaving region of men.
Teledermoscopy: The acquisition and storage of digital dermoscopic images are referred to as digital dermoscopy, while teledermoscopy (TDD) refers to transferring a digitalized dermoscopic image (visual data) for diagnosis, education, consultation or followup. Mobile TDD uses a smartphone to deliver the same type of service. Teledermoscopy can greatly reduce the number of unnecessary referrals, wait times, and the cost of providing and receiving skin care. Although the role of TDD in improving the reliability of telediagnosis and prognostication of patients with melanoma is well-established, the concept of TDD also has potential implications for delivery of better skin care services in the developing world, where primary care physicians (PCPs) who are non-dermatologists cater to a large proportion of patients with cutaneous disorders.
Although dermoscopy is an excellent tool for triage, it needs to be combined with the macro clinical picture and histopathology to be conclusive. The role of the dermatopathologist is vital in this regard. From what used to a clinicopathological correlation, we are moving towards a clinical-dermoscopic-pathological correlation.
As far as levels of evidence are concerned, a recently published Cochrane meta-analysis sums it up aptly-although the evidence-based is limited, the conclusion is that when specialists use dermoscopy, it is a better tool for the diagnosis of melanoma as compared to simple visual examination. Also, dermoscopy is more effective when interpreted with the actual patient, rather than with a dermoscopy image.