|Year : 2014 | Volume
| Issue : 2 | Page : 41-43
Role of dermoscopy in the diagnosis of pigmentary dermatoses in skin of color
Sunil Dogra, Ankit Mittal
Department of Dermatology, Venereology and Leprology, Post Graduate Institute of Medical Education and Research, Chandigarh, India
|Date of Web Publication||15-Dec-2014|
Department of Dermatology, Venereology and Leprology, Post Graduate Institute of Medical Education and Research, Chandigarh - 160 012
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Dogra S, Mittal A. Role of dermoscopy in the diagnosis of pigmentary dermatoses in skin of color. Pigment Int 2014;1:41-3
Dermatoscopy is correct English grammatically; however, dermoscopy is the term used by International Dermoscopy Society and is commonly used in literature. Other synonyms are epiluminescence microscopy and amplified surface microscopy. It is a noninvasive and in vivo diagnostic tool which visualizes subtle clinical patterns of skin structures not visible to the unaided eyes. Although it has been tried in a variety of skin disorders, but primarily used for the diagnosis of doubtful pigmented lesions.
Looking back to the history of dermoscopy, "dermatoscopy" term was introduced in 1920 by the German Dermatologist Johann Saphier, but Goldman was the first person to use it for pigmentary lesions in 1950s.
The basic principle underlying dermoscopy is transillumination of a lesion and studying it with a high magnification.  Fate of light incident on the skin includes reflection, refraction, diffraction and absorption. This fate is influenced by physical properties of the skin such as most of the light incident on dry, scaly skin is reflected, while smooth, oily skin allows most of the light to pass through it, reaching the deeper dermis. So to improve the visibility of subsurface skin structures linkage fluids are applied over the lesions to be studied to improve the translucency of the skin. Various linkage fluids used are oils (immersion oil, olive oil and mineral oil), water, an antiseptic solution and glycerin. Liquid paraffin and ultrasonography gel are other options that have shown good results besides being inexpensive, safe, easily available.
It has been used mostly in a white population in the evaluation of pigmented lesions and has shown superiority over clinical examination.  Although dermoscopy has not been used extensively in the nonwhite population, its role is also increasing in dark skin races. While using dermoscopy for pigmentory dermatoses, the primary aim is to differentiate benign from malignant lesions that is, melanocytic naevi from melanoma.
In practice of dermoscopy one has to be familiar with the terminology used for various structures seen during dermoscopic examination. Common terms used are pigment network, dots, globules, branched streaks, radial streaming, pseudopods, structureless areas, blotches, regression pattern, blue-white veil, vascular patterns, milia-like cysts, comedo-like opening, fissures and ridges, fingerprint-like structures, moth-eaten border, leaf-like areas, spoke wheel-like structures, large blue-gray ovoid nests, multiple blue-gray globules etc.  Complete description of these terms is beyond the scope of this article, but here we will discuss them briefly. The pigment network is a honeycomb-like network of pigmented "lines" and hypopigmented "holes." It can be either typical or atypical. A typical network is relatively uniform, regularly meshed, homogeneous in color, and usually thinning out at the periphery while an atypical network is nonuniform, with darker and/or broadened lines and "holes" that are heterogeneous in both area and shape, and this may end abruptly at periphery. Dots are small, round structures < 0.1 mm in diameter, which may be black, brown, gray, or blue-gray. Globules are round to oval, well-demarcated structures with size > 0.1 mm and may be brown, black, or red in color. Branched streaks are an expression of an altered pigmented network in which the network becomes disrupted or broken up. Radial streaming as name conveys is visible as parallel lines arranged radially and asymmetrically at the periphery of the lesion. Finger-like projections of dark pigment at the periphery of the lesion are called pseudopods. Areas that are devoid of any discernible structures such as dots, globules, network, etc., are named as "structureless areas." Blue-white veil appears as irregularly marginated, confluent blue pigmentation with overlying white, ground-glass haze. Milia-like cyst is visible as small, white or yellow cystic structure. Leaf-like areas are brown to blue-gray, discrete, structure resembling leaf-like patterns.
On the basis of the presence of above structures in various combinations, differential diagnosis of pigmented lesions is made. A famous approach for classification of pigmented lesions of the skin is "two-step procedure;" which was suggested in consensus net meeting in 2003.  In this two-step approach, the first step is to differentiate between a melanocytic and nonmelanocytic lesion. Features suggestive of a melanocytic lesion are aggregated globules, pigment network, branched streaks, homogeneous blue pigmentation (blue nevus), or a parallel pattern. If above features are not seen, the lesion should be looked for presence of milia-like cysts, comedo-like openings, irregular crypts, light brown fingerprint-like structures, or "fissures and ridges" (cerebriform appearance) pattern. These features are suggestive of seborrheic keratosis. In the absence of above features, the next step is to search for the presence of arborizing blood vessels (telangiectasia), leaf-like areas, large blue-gray ovoid nests, multiple blue-gray globules, spoke wheel areas or ulceration. If above features are present, they point to the diagnosis of basal cell carcinoma. If red or red-blue (to black) lagoons are present, the lesion should be considered as a hemangioma or an angiokeratoma. If none of these features are present, the lesion should still be considered to be a melanocytic lesion by exclusion.
Once the lesion is classified as melanocytic, the next step is to differentiate it into benign or malignant. There are various algorithms available for this. Most commonly used in practice are pattern analysis, the ABCD rule of dermoscopy, the 7-point checklist, the Menzies method, and the revised pattern analysis. Malignant lesions have asymmetry of the pattern, much architectural disorder, and show many colors as compared benign lesion have symmetry of the pattern, architectural order, few colors, and homogeneity. Various algorithms give different grades or scores to above-mentioned features, and if the total score is above cut-off or a criterion is fulfilled, lesion is considered malignant. Although none of these methods is universally preferred, but in a study by Argenziano and Soyer  pattern analysis produced the best diagnostic performance, while ABCD rule, Menzies method, and 7-point checklist have similar sensitivity compared with pattern analysis but about 10% less speciﬁcity and lower positive likelihood ratios.
Before knowing about dermoscopy in dark skin, first we should know how pigmentary lesions mainly melanoma is different in dark skin population from that of white skin. Melanoma is more common in the white population compared to nonwhite. In a study by Cormier et al.  among US population, the average annual age-adjusted melanoma incidence per 100,000 persons was 18.4 for whites compared with 2.3, 0.8, 1.6, and 1.0 for Hispanics, African Americans, American Indians. Probably such low incidence of melanoma in the nonwhite population compared to whites is the reason for less popularity of dermoscopy in this population. Still melanoma is the third most common cutaneous malignancy in Blacks, Asians, Hispanics, and Caucasians.  Melanoma in nonwhite races most often arise on nonsun-exposed skin with less pigment, particularly acral areas of the lower extremities. Acral-lentiginous melanoma is the most common histologic subtype in Asians and blacks, whereas superficial spreading melanoma is the most frequent subtype in Caucasians.  Important point to remember is that pigmented lesions in the dark skin are often more difficult to notice and therefore melanomas are often detected at late stages.  May be that's why melanoma in nonwhite individuals is thought to have a poorer prognosis than a white population. 
Very few studies reporting efficacy of dermoscopy in dark skin for pigmentary lesions have been performed. Giorgi et al.  conducted dermoscopic examination of pigmentary lesions in black patients and concluded that although examination of pigmentary lesions with naked eye is more difficult in dark skin, but dermoscopy significantly reduces this difficulty because the dermoscopic features remain the same as white skin. While using dermoscopy in dark skin stronger source of light may be required as darker skins tend to absorb larger amounts of light rays. 
As previously mentioned, melanoma in dark skin is more common on acral skin, so while examining nonwhite population one should know thoroughly about special patterns seen in acral skin on dermoscopy. Parallel pattern is exclusively found on the palms and soles due to the particular anatomy of these areas.  Parallel ridge pattern is band like pigmentation on ridges of skin markings. Irregular diffuse pigmentation is defined as diffuse pigmentation with variable shades from tan to black, occasionally even with a grayish tone. Parallel linear pigmentation along sulci of skin markings is known as parallel furrow pattern. Lattice like pattern is formed by linear pigmentation following and crossing sulci of skin markings. Fibrillar pattern contains numerous fine fibrillar or filamentous pigmentation running in slanting direction to skin markings. Out of these, parallel ridge pattern and irregular diffuse pigmentation have been found to be highly suggestive of malignant melanoma and melanoma in situ on acral volar skin. , In contrast the parallel furrow pattern and the lattice like pattern are the most prevalent dermoscopic features observed in benign melanocytic nevi. , In a multicenter study it was observed that the positive predictive value of the parallel ridge pattern was significantly higher than that of irregular diffuse pigmentation in all melanomas, including invasive and in situ melanomas, but the differences were much more prominent in case of melanoma in situ.  Other common pigmented lesions such as seborrhoeic keratosis and basal cell carcinoma, which can be diagnostically difficult to differentiate, are not found on acral volar skin. Black heel due to subcorneal hematoma, ethnic-type volar pigmentation, and pigmented macules of Peutz-Jeghers syndrome are important differentials of melanoma on acral skin. Although these conditions may show similar dermoscopic patterns to the parallel ridge pattern  but usually these can be easily differentiated by their characteristic clinical and/or dermoscopic presentation.  Therefore, differentiation between malignant melanoma and melanocytic nevus is the major practical concern on this anatomic site. Dermoscopy have been found useful in subungual melanomas also,  which is another common location for melanoma in nonwhite population.  Another aspect of lesion involving of acral skin is that the biopsy of lesions on sole and of the nail is difficult to perform, so dermoscopy could be of great help in avoiding unnecessary biopsies.
Mucosal pigmented lesions can be another area of interest where dermoscopy may be useful in darker skin, as the mucosa is another common site for melanoma in this population. Although the usefulness of dermoscopy for pigmented mucosal lesions is not well established, dermoscopy has shown promise in recent studies. Results of a multicenter, retrospective, observational study  of 140 cases have shown that the presence of at least 1 of blue, gray, or white color and structureless zones in dermocopy had a relatively good diagnostic accuracy in differentiating between malignant and benign mucosal lesions.
Beside this, dermoscopy has been used in facial pigmentary dermatoses which are more common in dark Asian populations. Exogenous ochronosis can be seen in dark skinned patients of melasma as a side effect of hydroquinone. Exogenous ochronosis has characteristic features on dermatoscopy such as accentuation of the normal pseudo-rete of the facial skin with amorphous densely-pigmented structures obliterating some follicular opening and multiple thin, short arciform structures.  Hence, dermoscopy may obviate the need for an invasive procedure of biopsy for its diagnosis. Riehls melanosis another facial pigmentary disorder of dark skin population, which poses a diagnostic challenge in clinical practice because of variable morphology has shown distinctive features in recent studies. In a study by Wang and Xu  pseudo network and grey dots/granules were the most suggestive dermoscopic features.
Overall dermoscopy is underused in dark skin population, but its use is on the rise in recent times. Beside naevi and cutaneous malignancies mainly melanoma, its utility has been expanding to other category of pigmentary disorders. But, there is a need for further studies to generate adequate amount of data to show diagnostic value of dermoscopy in this population.
| References|| |
Stolz W, Bilek P, Landchaer M, Cogneta A, editors. Basis of dermatoscopy and skin-surface microscopy. Color Atlas of Dermatoscopy. 1 st
ed. Germany: Blackwell Publications; 1994. p. 7-10.
Argenziano G, Soyer HP. Dermoscopy of pigmented skin lesions - A valuable tool for early diagnosis of melanoma. Lancet Oncol 2001;2:443-9.
Braun RP, Rabinovitz HS, Oliviero M, Kopf AW, Saurat JH. Dermoscopy of pigmented skin lesions. J Am Acad Dermatol 2005;52:109-21.
Argenziano G, Soyer HP, Chimenti S, Talamini R, Corona R, Sera F, et al.
Dermoscopy of pigmented skin lesions: Results of a consensus meeting via the Internet. J Am Acad Dermatol 2003;48:679-93.
Cormier JN, Xing Y, Ding M, Lee JE, Mansfield PF, Gershenwald JE, et al.
Ethnic differences among patients with cutaneous melanoma. Arch Intern Med 2006;166:1907-14.
Gloster HM Jr, Neal K. Skin cancer in skin of color. J Am Acad Dermatol 2006;55:741-60; quiz 761.
Bellows CF, Belafsky P, Fortgang IS, Beech DJ. Melanoma in African-Americans: Trends in biological behavior and clinical characteristics over two decades. J Surg Oncol 2001;78:10-6.
Cress RD, Holly EA. Incidence of cutaneous melanoma among non-Hispanic whites, Hispanics, Asians, and blacks: An analysis of california cancer registry data, 1988-93. Cancer Causes Control 1997;8:246-52.
de Giorgi V, Trez E, Salvini C, Duquia R, De Villa D, Sestini S, et al.
Dermoscopy in black people. Br J Dermatol 2006;155:695-9.
Saida T, Oguchi S, Miyazaki A. Dermoscopy for acral pigmented skin lesions. Clin Dermatol 2002;20:279-85.
Kawabata Y, Tamaki K. Distinctive dermatoscopic features of acral lentiginous melanoma in situ
from plantar melanocytic nevi and their histopathologic correlation. J Cutan Med Surg 1998;2:199-204.
Saida T, Oguchi S, Ishihara Y. In vivo
observation of magnified features of pigmented lesions on volar skin using video macroscope. Usefulness of epiluminescence techniques in clinical diagnosis. Arch Dermatol 1995;131:298-304.
Saida T, Miyazaki A, Oguchi S, Ishihara Y, Yamazaki Y, Murase S, et al.
Significance of dermoscopic patterns in detecting malignant melanoma on acral volar skin: Results of a multicenter study in Japan. Arch Dermatol 2004;140:1233-8.
Ronger S, Touzet S, Ligeron C, Balme B, Viallard AM, Barrut D, et al.
Dermoscopic examination of nail pigmentation. Arch Dermatol 2002;138:1327-33.
Blum A, Simionescu O, Argenziano G, Braun R, Cabo H, Eichhorn A, et al.
Dermoscopy of pigmented lesions of the mucosa and the mucocutaneous junction: Results of a multicenter study by the International Dermoscopy Society (IDS). Arch Dermatol 2011;147:1181-7.
Mishra SN, Dhurat RS, Deshpande DJ, Nayak CS. Diagnostic utility of dermatoscopy in hydroquinone-induced exogenous ochronosis. Int J Dermatol 2013;52:413-7.
Wang L, Xu AE. Four views of Riehl's melanosis: Clinical appearance, dermoscopy, confocal microscopy and histopathology. J Eur Acad Dermatol Venereol 2014;28:1199-206.