INTRODUCTION — Dermoscopy is a noninvasive, in vivo technique primarily used for the examination of cutaneous lesions [1]. Dermatoscopy, epiluminescence microscopy, incident light microscopy, and skin-surface microscopy are synonyms.
Dermoscopy is performed with a handheld instrument called a dermatoscope. The procedure allows for the visualization of subsurface skin structures in the epidermis, at the dermoepidermal junction, and in the papillary dermis; these structures are usually not visible to the naked eye [2-4]. The dermoscopic images may be photographed or recorded digitally for storage or sequential monitoring for change.
The basic principles of dermoscopy will be discussed in this topic. The dermoscopic diagnosis of skin lesions, including those in special anatomic areas (eg, face, volar surfaces of palms and soles, mucosal surfaces, and glabrous skin in genital area), dermoscopy of nail pigmentation, and algorithms used for skin cancer triage are discussed separately.
●(See "Dermoscopic evaluation of skin lesions".)
●(See "Dermoscopy of pigmented lesions of the palms and soles".)
●(See "Dermoscopy of facial lesions".)
●(See "Dermoscopy of mucosal lesions".)
●(See "Dermoscopy of nail pigmentations".)
●(See "Overview of dermoscopy of the hair and scalp".)
●(See "Dermoscopic algorithms for skin cancer triage".)
DERMOSCOPY PHYSICS — Ambient light is reflected, scattered, or absorbed by objects. Under normal conditions, most of the light is reflected by the skin surface because of the higher refractive index (RI) of the stratum corneum (1.55) compared with that of the air (1.00).
Reduction of skin surface reflection allows for the visualization of deeper epidermal and dermal structures. This reduction can be achieved by affixing a glass plate (RI: 1.52) to the stratum corneum (RI: 1.55) and using an RI-matched immersion fluid as an interface or by using cross polarizing filters [5-7].
Several immersion fluids have been used, including water, alcohols (ethanol and isopropanol), oils (mineral oil, immersion oil, and olive oil), and water-soluble gels (ultrasound gel, cosmetic gels). Alcohols (in particular isopropyl alcohol 70%) are the preferred immersion liquid due to their low viscosity, amphiphilic properties (ie, both water and lipid soluble), disinfectant capabilities, and image clarity. However, on some specific sites such as the mucosae and areas around the eyes and nails, water-soluble gels are preferred over alcohol since they are noncaustic and have higher viscosity [6].
Alternatively, reduction of the skin surface reflection can be achieved by using polarized light [8]. Polarized light dermoscopy utilizes two orthogonally placed filters in a process called cross-polarization (figure 1). After reaching the skin surface, part of the polarized light is reflected by the stratum corneum maintaining its polarization, whereas part enters the skin and is scattered back from the deeper layers, losing its polarization. The light reflected by the skin surface, responsible for the glare of the skin, is blocked by the cross-polarized filter, since this light maintains its polarization. The backscattered light from the deeper layers passes through the cross-polarized filter since some of the polarized light has lost its angle of polarization. This makes the subsurface structures visible to the eye [7-9].
TYPES OF DERMATOSCOPES — Dermatoscopes consist of a transilluminating light source and magnifying optics. The most commonly used dermatoscopes have a 10-fold magnification [4].
Three types of dermatoscopes are available:
●Nonpolarized light, contact
●Polarized light, contact
●Polarized light, noncontact
Nonpolarized and polarized light dermoscopy provide complementary information (table 1) [5,7,9,10]. Deeper structures are more conspicuous with polarized dermoscopy; in contrast, superficial structures are more conspicuous with nonpolarized dermoscopy. For example, epidermal structures (eg, milia cysts and comedo-like openings in seborrheic keratoses and blue-white veil due to orthokeratosis) are more conspicuous with nonpolarized dermoscopy, whereas blood vessels and shiny, white structures (shiny, white streaks/lines; shiny, white blotches; and strands and rosettes) are better visualized with polarized light dermoscopy [5,7,11]. Structures visible in one mode and not in the other will blink when viewed with dermatoscopes that can toggle between polarized and nonpolarized light [12].
COLORS AND STRUCTURES — The visualization of colors and structures in the epidermis and papillary dermis has generated a new terminology for the morphologic description of skin lesions [13]. A histologic correlation has been established for most of the structures seen with dermoscopy [14-17].
Colors — The colors seen with dermoscopy include yellow, red, brown, blue, gray, black, and white (figure 2D) [18,19]. Melanin is the most important chromophore in pigmented lesions. The color of melanin as seen on the surface of the skin depends upon its concentration and its localization in the skin; it usually appears black if located in the stratum corneum, brown if in the epidermis and superficial dermis, and gray/blue to blue if in the dermis. The color red is determined by vascularity; a thrombus will appear black. White is associated with collagen/fibrosis, yellow is associated with keratin or sebum, and orange can be associated with serum crusts.
Structures — The structures visualized in skin lesions are determined by the distribution and amount of melanin, keratin, collagen, and vascularity [10,13,18,20-22]:
●Pigment network, negative network, angulated lines, streaks, aggregated or peripheral rim of globules, and homogeneous blue pigmentation are the hallmark of melanocytic lesions (picture 1A-C).
●Arborizing vessels; leaf-like structures; spoke wheel-like structures; concentric, globular structures; large, blue/gray, ovoid nests; multiple blue/gray, nonaggregated globules; shiny, white blotches and strands; multiple aggregated, yellow to whitish globules [23]; ulceration; and multiple erosions are features of basal cell carcinomas (picture 2).
●Glomerular vessels, white circles, rosettes, white/yellow scale, brown circles, and brown dots/globules aligned radially are structures of squamous cell carcinomas (picture 3).
●Milia-like cysts, comedo-like openings, finger print-like structures, moth-eaten borders, gyri and sulci, and sharp demarcation are characteristic of seborrheic keratoses (picture 4).
Red or blue/purple/black lagoons are seen in cherry angiomas or angiokeratomas (picture 5). (See "Dermoscopic evaluation of skin lesions", section on 'Step 1: Benign lesions'.)
●Atypical pigment network; negative network; shiny, white streaks/lines; atypical blotches; blue-white veil; atypical vascular pattern; irregular streaks; atypical dots or globules; angulated lines creating a zigzag pattern or polygons; regression structures; and peripheral, tan, structureless areas are some of the features associated with melanoma (picture 6A-C). (See "Dermoscopic evaluation of skin lesions", section on 'Other algorithms and methods'.)
A detailed description of the dermoscopic structures visualized in melanocytic and nonmelanocytic lesions and their histologic correlates is provided in the figures (figure 2A-C).
The diagnostic criteria for benign and malignant melanocytic and nonmelanocytic skin lesions are discussed separately. (See "Dermoscopic evaluation of skin lesions".)
Vascular structures — In amelanotic and hypomelanotic lesions, the vascular structures (morphology, distribution, and arrangement) may provide the only clues to the diagnosis. In pigmented lesions, the pigmented structures provide the primary clue to the diagnosis, and vascular morphology provides additional secondary clues to the diagnosis [24,25].
Noncontact polarized light is the preferred type of dermatoscope for the visualization of blood vessels. However, if a contact dermatoscope is utilized, an ultrasound gel should be used as a liquid interface since the gel acts as a cushion and reduces the need for pressure being applied to the skin, preventing the blanching of the vessels.
The dermoscopic evaluation of vascular structures includes morphology (eg, dotted; linear, irregular, or serpentine; comma like; corkscrew; looped or hairpin; glomerular or coiled; arborizing or branched), distribution (ie, focal, diffuse, central, peripheral, or random), arrangement (eg, crown, string of pearls, clustered, radial), and presence of a white or pink halo (table 2A-B) [21,24,26-31].
Although some vessel morphologies are most commonly associated with certain types of lesions (eg, arborizing vessels are common in basal cell carcinoma), the presence of a given vessel morphology is not exclusive to a particular diagnosis. For example, dotted vessels can be seen in melanocytic tumors and also in squamous cell carcinoma (picture 3), basal cell carcinoma, porokeratosis, clear cell acanthoma, and psoriasis [26,29,30,32,33]. Similarly, glomerular vessels are most commonly associated with squamous cell carcinoma/Bowen disease (picture 3), but they can also be seen in clear cell acanthoma. Polymorphous vessels are typically associated with melanoma but can also be seen in basal cell carcinoma [29]. Arborizing vessels are commonly seen in basal cell carcinoma, but they can also be seen in melanoma and intradermal nevi. Hairpin vessels are commonly associated with seborrheic keratoses, although they can also be seen in melanoma. Despite this overlap, the positive predictive value for a given vessel morphology can guide the clinician to the correct diagnosis if the clinical context is carefully considered (table 2A-B). (See "Dermoscopic evaluation of skin lesions", section on 'Other algorithms and methods'.)
CLINICAL ROLE OF DERMOSCOPY — The importance of dermoscopy in the in vivo diagnosis of melanoma is well recognized [34], following the identification of a large set of dermoscopic features in benign and malignant lesions together with their histopathologic correlates [16-18,35].
Dermoscopy requires some formal training to be effectively practiced. Online resources and tutorials on dermoscopy can be found at www.dermnetnz.org/cme/dermoscopy-course/introduction-to-dermoscopy.com, www.dermoscopy-ids.org/webcasts.com, www.genomel.org/dermoscopy, www.healthcert.com/pcder-free-module.com, or www.dermoscopedia.org.
Cross-sectional studies, randomized trials, meta-analyses, and a 2018 Cochrane systematic review have indicated that dermoscopic examination has a higher discriminatory power than naked-eye examination to detect skin cancer, including melanoma either in experimental or real-life clinical settings [13,34,36-44]. For clinicians with at least minimal training in dermoscopy, the addition of this procedure to the clinical examination increases the accuracy of the in vivo diagnosis of skin cancer and reduces the number of unnecessary biopsies [37] (see "Evaluating diagnostic tests"). In fact, 86 percent of dermoscopy users from 32 European countries reported that dermoscopy increased their melanoma detection rate, and 70 percent reported that dermoscopy decreased the number of unnecessary biopsies of benign lesions they performed [45].
Diagnostic accuracy for melanoma — Three meta-analyses and a 2018 Cochrane systematic review have shown that dermoscopy improves diagnostic accuracy for melanoma over naked-eye examination [34,38-40]. In one of these meta-analyses including nine studies performed in clinical settings, the authors reported an odds ratio for the diagnosis of melanoma of 9 (95% CI 1.5-54.6) for dermoscopy plus clinical examination, compared with clinical examination alone [39]. The summary sensitivity was 90 percent (95% CI 80-95) and the specificity was 90 percent (95% CI 57-98) for dermoscopy plus clinical examination; sensitivity was 71 percent (95% CI 59-82) and specificity was 81 percent (95% CI 48-95) for clinical examination alone. Sensitivity improved without a decrease in specificity, meaning that the higher rate of melanoma detection was not associated with a concomitant increase in the number of unnecessary excisions of benign lesions.
Several factors may affect the diagnostic performance of dermoscopy:
●Experience of the examiner
●Diagnostic algorithm and threshold for a positive test
●Prevalence of melanoma in the patient population examined
●Clinical context and patient-related factors [46,47]
In a systematic review of 27 studies performed in clinical and experimental settings, the diagnostic accuracy of dermoscopy was lower for inexperienced examiners compared with experts, and was inversely proportional to the prevalence of melanoma in the sample [40]. The degree of experience improved the diagnostic accuracy of complex algorithms, such as pattern analysis, whereas it did not affect the performance of simpler algorithms, such as the ABCD (asymmetry, border sharpness, colors, and dermoscopic structures) rule of dermoscopy.
Two clinical trials performed in primary care settings have shown that a short training in dermoscopy enables nondermatologists to use simplified diagnostic algorithms and improve their accuracy in the diagnosis of melanoma [37,48,49].
●In one trial, 73 primary care physicians received one-day training in skin cancer detection and dermoscopy and were subsequently randomly assigned to use a polarized light handheld dermatoscope or the naked eye to assess the pigmented lesions of their patients for a period of 16-months [37]. All patients were also independently evaluated by expert dermatologists. The sensitivity for the referral of suspicious lesions was significantly higher in the dermoscopy group, compared with the naked-eye examination group (79 and 54 percent, respectively), without difference in specificity (71 and 72 percent, respectively).
●A 2019 systematic review of 23 randomized and observational studies performed in primary care settings confirmed that dermoscopy, with appropriate training, was associated with improved diagnostic accuracy for melanoma and benign lesions and reduced unnecessary excisions and referrals [50].
●A 2021 scoping review also demonstrated that dermoscopy training in the primary care setting is generally associated with improved diagnostic ability [51].
However, primary care clinicians who attend short dermoscopy trainings may not continue to use it in longer-term practice [51,52], and the minimal amount of training required to achieve competence in dermoscopy has not been determined.
Indications — Dermoscopy aids in the evaluation of pigmented and nonpigmented skin lesions and helps in the decision-making process as to whether or not a biopsy is warranted to rule out skin cancer. Dermoscopic examination is especially useful for patients with multiple common and/or atypical nevi who are at increased risk of melanoma. In those patients, dermoscopic examination of their nevi helps identify suspicious lesions not found with naked-eye preselection [53].
Although it will be beneficial to examine as many lesions as possible in patients with multiple nevi, special attention should be paid to the following [54]:
●Any new or changing lesion
●Any lesions that are a concern (including symptomatically) for the patient
●Outlier skin lesions that are clinically different from the other lesions (the "ugly duckling" sign)
●Lesions that appear clinically suspicious for skin cancer
In addition, dermoscopy has been shown to be a useful tool in the evaluation of other dermatologic entities, such as inflammatory and infectious diseases and hair and nail disorders. (See "Dermoscopy of nail pigmentations" and "Dermoscopy of nonpigmented nail lesions".)
Purposes — Dermoscopy may have different purposes depending upon the clinical setting in which it is used.
In general dermatology and in primary care practices, the primary purpose of dermoscopy is the evaluation of pigmented and nonpigmented skin lesions to decide whether or not a lesion should be biopsied or referred. For this purpose, a minimal amount of training is needed [37,55-57]. Several algorithms have been developed for this aim. (See "Dermoscopic algorithms for skin cancer triage".)
In specialized dermatologic settings, which include management of high-risk patients (eg, patients with the dysplastic/atypical nevus syndrome), the main purposes of dermoscopy are to differentiate early melanoma from benign skin lesions and to minimize the unnecessary excision of nevi. Subtle signs of melanoma may be detected on dermoscopy by experienced clinicians before they become clinically evident to the naked eye.
Digital dermoscopy is useful for long- and short-term follow-up of patients with multiple common and atypical nevi [58-63]. Sequential digital dermoscopy imaging (SDDI) involves the capture and comparison of sequential dermoscopic images of one or more melanocytic lesions for short-term (three to four months) or long-term (6 to 12 months) surveillance. Several studies have indicated that SDDI has high sensitivity and specificity for detecting in situ or thin invasive melanomas that are difficult to diagnose otherwise [60-62,64]. One study showed that in the primary care setting the combination of dermoscopy and short-term digital monitoring reduced the excision or referral of benign pigmented skin lesions by 56 percent and increased the sensitivity for diagnosing melanoma from 38 to 72 percent [57].
In addition to its conventional use, dermoscopy has also been shown to improve the clinical diagnosis in other fields of dermatology, including infections/infestations as well as inflammatory skin diseases and hair diseases [65].
Benefits
●Dermoscopy improves the diagnosis of melanocytic lesions in clinical practice. Several meta-analyses of studies performed in experimental and clinical settings have indicated that dermoscopy increases the sensitivity for the diagnosis of melanoma without decreasing the specificity, compared with the naked-eye examination [34,38-40].
●Dermoscopy improves the confidence in the diagnosis of benign pigmented lesions, reducing the number of unnecessary biopsies. In a randomized trial, dermatologists using dermoscopy, compared with those using naked-eye examination, referred fewer patients for excision of benign lesions (9 versus 16 percent) without missing malignant lesions [41]. Several retrospective studies examined the numbers of excised benign and malignant lesions in dermatologic practices before and after the introduction of dermoscopy [66,67]. In one study, the ratio between benign and malignant excised lesions decreased from 18:1 to 4:1 over a three-year period [66].
●Dermoscopy allows digital surveillance and monitoring of melanocytic lesions in patients with multiple common or atypical nevi [58-63].
●Dermoscopy is useful in the diagnosis and differentiation of nonmelanocytic benign and malignant tumors such as basal cell carcinoma, dermatofibroma, seborrheic keratosis, and hemangioma [10,21,26,28].
Limitations
●The diagnostic accuracy of dermoscopy may be poorer than naked-eye examination when performed by individuals with limited experience in the interpretation of dermoscopy [40]. Dermoscopy requires at least a minimal amount of training to provide advantage over the clinical examination [68]. The correct interpretation of dermoscopic images depends upon knowledge of the significance of colors and structures manifested by a lesion. In addition, examining a lesion with reference to the clinical context and comparison to surrounding lesions is also important for rendering a correct diagnosis [46].
●Even in expert hands, dermoscopy may fail to recognize melanomas that lack specific dermoscopic criteria (featureless melanomas) or melanomas masquerading as inflammatory or benign lesions, such as Spitzoid melanomas, amelanotic melanomas, nodular melanomas, nevoid melanomas, desmoplastic melanomas, or verrucous melanomas [69,70].
●Although digital dermoscopic images are suitable for distance consultation, interpretation of dermoscopic photographs may be slightly less accurate than in-vivo dermoscopy [71,72].
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Dermoscopy".)
SUMMARY AND RECOMMENDATIONS
●Definition – Dermoscopy is a noninvasive, in vivo technique primarily used for the examination of skin lesions. A handheld instrument called a dermatoscope, consisting of a light source and magnifying optics, allows the visualization of subsurface skin structures that are usually not visible to the naked eye. (See 'Dermoscopy physics' above and 'Types of dermatoscopes' above.)
●What dermoscopy visualizes in skin lesions – Colors and structures visualized in skin lesions are mainly related to the amount, distribution, and localization of melanin, vasculature structures, collagen, keratin, and serum crusts (figure 2A-D and table 2A-B):
•Melanocytic lesions – Pigment network, negative network, angulated lines, streaks, aggregated globules or peripheral rim of globules, and homogeneous, blue pigmentation are the hallmark of melanocytic lesions (picture 1A-C).
•Basal cell carcinoma – Arborizing vessels; leaf-like structures; spoke wheel-like structures/concentric globules; ovoid or round, blue/gray, nonaggregated dots/globules; multiple aggregated, yellow to whitish globules; and shiny, white blotches and strands are features of basal cell carcinomas (picture 2).
•Squamous cell carcinoma – Glomerular vessels, white circles, rosettes, white/yellow scale crust, brown circles, and brown dots/globules aligned radially are structures of squamous cell carcinomas (picture 3).
•Seborrheic keratosis – Milia-like cysts, comedo-like openings, and gyri and sulci are characteristic of seborrheic keratoses (picture 4).
•Cherry angiomas/angiokeratoma – Red or blue/purple/black lagoons are seen in cherry angiomas or angiokeratomas (picture 5). (See "Dermoscopic evaluation of skin lesions", section on 'Step 1: Benign lesions'.)
•Melanoma – Atypical pigment network; negative network; shiny, white streaks/lines; atypical blotches; blue-white veil; atypical vascular pattern; irregular streaks; atypical dots or globules; angulated lines creating a zigzag pattern or polygons; regression structures; and peripheral, tan, structureless areas are some of the features associated with melanoma (picture 6A-C). (See "Dermoscopic evaluation of skin lesions", section on 'Other algorithms and methods'.)
●Advantages of dermoscopic examination:
•For clinicians who have been formally trained, the addition of dermoscopy to clinical examination improves the sensitivity and specificity of the in vivo diagnosis of skin cancer, including melanoma. In particular, dermoscopy improves the confidence in the diagnosis of benign lesions and reduces the number of unnecessary biopsies. However, even in expert hands, dermoscopy may fail to recognize melanomas lacking specific dermoscopic features. (See 'Diagnostic accuracy for melanoma' above and 'Benefits' above and 'Limitations' above.)
•Dermoscopy may be useful in patients with multiple common or atypical nevi who are at increased risk for melanoma. Special attention should be paid to lesions with reported history of change and lesions appearing clinically different from the other lesions (the "ugly duckling" sign) or clinically suspicious of melanoma. (See 'Indications' above.)
آیا می خواهید مدیلیب را به صفحه اصلی خود اضافه کنید؟