[Academic Presentation] Advances in the Application of Dermoscopy to Skin Diseases in Atypical Sites

Article reprinted from: Chinese Medical Abstracts – Dermatology, Issue 3, 2017.

Authors: Li Qiannan, Kong Xiangjun, Liu Yuanyuan, Zhou Jing, Jin Ke, Zhang Junling

Dermoscopy is a non‑invasive in vivo diagnostic technique whose fundamental principle involves using an optical system to magnify the area of interest and, through liquid immersion or polarized light, minimizing unwanted reflections from the stratum corneum. This process generates a magnified image on the retina, closely linking macroscopic and microscopic features of skin lesions. Dermoscopy not only aids in diagnosis and differential diagnosis but also helps assess treatment efficacy and guide pharmacologic management. In clinical practice, many dermatologic conditions present with inconspicuous characteristic findings, necessitating ancillary diagnostic modalities; however, such methods often have site‑specific limitations. For example, histopathologic biopsy of the lip or genital region may cause functional impairment and is therefore poorly tolerated by patients. By contrast, dermoscopy is easy to perform and entirely non‑invasive, making it widely applicable across a broad spectrum of skin disorders and particularly advantageous for evaluating lesions in challenging anatomical locations.

1. Microscopic Features of Certain Scalp Disorders

1. Hair loss category

1. 1. 1 Alopecia Areata Among the microscopic features of alopecia areata, the yellow dot sign is the most frequently observed; it has high sensitivity but low specificity and can serve as an initial screening indicator. The black dot sign, broken hairs, and exclamation‑mark hairs all exhibit high specificity, suggesting active disease; among these, exclamation‑mark hairs are diagnostically significant and tend to disappear earliest following treatment. In patients with acute alopecia areata, microscopy reveals exclamation‑mark hairs and/or vellus‑like hairs, with some hair shafts showing proximal thickening accompanied by increased pigmentation. In chronic alopecia areata, the findings include markedly dilated follicular openings, sometimes associated with keratin plugs.

1. 1. 2 Androgenetic alopecia Androgenetic alopecia is more common in men, and its dermoscopic features include hair diameter thinning in more than 20% of hairs, an increase in vellus hairs, localized areas of alopecia, hyperpigmentation, and the yellow dot sign. Hair diameter thinning in more than 20% of hairs is an important early indicator; the yellow dot sign corresponds to sebaceous gland enlargement and may appear during the progressive phase; hyperpigmentation may be associated with prolonged direct sun exposure following hair loss. In female pattern hair loss, the hallmark finding is localized areas of alopecia, with less pronounced variation in hair shaft thickness compared to male patients.

1. 1.3 Discoid lupus erythematosus In alopecia associated with discoid lupus erythematosus (DLE), microscopic findings may include a reduction or disappearance of follicular openings, telangiectasia, scalp atrophy, follicular keratin plugs, erythematous‑white lesions, and scaling. Prominent features include branched telangiectasias, a decreased number of follicular openings, and keratin plugs; the complete obliteration of follicular openings typically occurs in the late stage.

1. 1. 4 Other In patients with tinea capitis, microscopic examination may reveal comma‑shaped hairs, perifollicular white patches, and greasy scales. Among these, infection with Microsporum canis shows only comma‑shaped hairs, whereas infection with Trichophyton gypsum reveals both comma‑shaped hairs and spiral‑shaped hairs; reports regarding the presence of these features in infections caused by Trichophyton violaceum remain inconsistent. In patients with trichotillomania, microscopy demonstrates not only the “black dot sign,” broken hairs, newly emerging short hairs, and an increase in vellus hair, but also blood crusts, scratch marks, hair follicle openings devoid of shafts, “V‑shaped” hairs, and structural abnormalities such as split and curled distal ends of the hair shafts. Folliculitis with alopecia is characterized by clustered hairs and may also present with follicular or perifollicular pustules; in advanced stages, the follicular ostia may disappear. In the acute phase of mucinous alopecia, broken hairs and the black dot sign are observed, with follicular ostia appearing depressed as the hallmark feature. In pseudo‑alopecia due to lichen planopilaris, perifollicular scales, white dots, and bluish‑gray punctate lesions around the follicular structures are evident; under the microscope, wickham‑like structures are often identifiable.

1. 2 Other diseases Under microscopic examination, the principal features of scalp psoriasis are white scales; at low magnification, one can observe punctate or globular vessels arranged in a regular pattern, while at high magnification, glomerular‑like vascular structures predominate. In contrast, scalp seborrheic dermatitis reveals yellowish scales under the microscope; at low magnification, various types of vessels are seen, and at high magnification, fine branching vessels and atypical vessels appear in an irregular arrangement. Other inflammatory conditions of the scalp have been reported less frequently to date.

2. Microscopic Features of Disease Type A

2.1 Diseases with black nails as a clinical manifestation

2. 1. 1 Melanocytic nevus of the nail bed Under the microscope, the nail matrix nevus exhibits pigmented bands composed of regularly arranged, longitudinally parallel pigment lines. The pigment lines are generally uniform in thickness and spacing, with no obvious interruptions. Occasionally, small, regular black granules measuring less than 0.1 mm in diameter may be observed, which could represent intracellular melanin inclusions.

2. 1. 2 Melanoma of the skin The most common dermoscopic findings in nail melanoma are irregular brown linear structures against a brownish-gray background of the nail plate, with uneven color, thickness, and spacing, as well as loss of parallelism. In some lesions, dermoscopy may reveal nail plate disruption or sharply demarcated, differently colored punctate or linear hemorrhages. The lunula or periungual skin is often involved as well, resulting in hyperpigmentation (Hutchinson’s sign). The ABCDEF criteria proposed by Levi et al. provide useful guidance for the early diagnosis of nail melanoma.

2. 1. 3 Subungual hemorrhage The most common dermoscopic finding in subungual hemorrhage is a homogeneous pattern, though pigmentation may also appear as banding or involve the entire nail. Depending on the duration of the injury, dermoscopy reveals uniform reddish to dark red‑black pigmentation; proximally, small reddish‑black globules may be observed, while distally, reddish‑black lines are sometimes seen.

2. 1. 4 Onychomycosis The definitive diagnosis of onychomycosis relies on the results of fungal testing. Dermoscopy offers a degree of diagnostic utility; under dermoscopy, yellow‑white longitudinal striations with a serrated appearance may be observed, with the serrated peaks oriented toward the proximal nail bed, along with other pigmented parallel bands that resemble an aurora. In fungal black nail, dermoscopy reveals longitudinal black discoloration, with a proximally broad and distally tapering pigmentary band indicating a distal‑to‑proximal progression of infection; multiple punctate expanding pigmented spots may also be seen in the proximal portion of the band.

2. 2 Other On dermoscopy, nail psoriasis typically presents with punctate or linear vascular structures and white scales against a red or gray‑red background; the nail plate may show onycholysis, splinter hemorrhages, and hyperkeratosis of the nail bed. In lichen planus of the nails, longitudinal ridging, nail plate fragmentation, pitting, and wing‑like paronychia are observed. Green nails demonstrate subungual green pigmentation on dermoscopy, with a fading border marking the onset of nail plate separation. Dermoscopic features of onychophagy include shortening of the nail plate, exposure of the nail bed epithelium, and wrinkling of the nail folds, often accompanied by bleeding.

3. Microscopic Features of Diseases in Other Special Sites

3. 1 Genital area Under dermoscopy, pubic lice appear as brownish‑tan parasites measuring approximately 0.9 mm × 1.2 mm, with crab‑like legs that firmly grasp the hair shafts. For genital warts, the lesion surface is typically rough, and one or more of the following patterns—finger‑like, globular, mosaic‑like, or irregular—can be observed on the same base. Vascular structures resembling hairpins, punctate vessels, and glomerular‑like formations are also evident, with glomerular‑like patterns being most common. In reported cases of Bowenoid papulosis, linearly arranged, regularly spaced brownish or grayish punctate pigmentary structures at the lesion margins, along with widely dispersed, irregularly organized punctate vascular structures, can be seen under dermoscopy.

3. 2 lips Research has shown that, under the microscope, oral lichen planus presents as pearly‑white striae; chronic discoid lupus erythematosus of the lip reveals irregular white patches and linear vascular patterns; and chronic cheilitis is characterized by glomeruli and white or yellowish scales. In the early stages, all three conditions exhibit desquamation, erythema, erosion, and crusting. Furthermore, in melasma of the lips, the microscopic findings include a homogeneous brown to black structure with linear or curvilinear pigmentary strands arranged in parallel; whereas in Laugier–Hunziker syndrome, lip lesions display a regular brown reticular pattern resembling parallel grooves, within which linear or branching vessels can be observed.

4. Summary

Skin diseases of special anatomical sites are frequently encountered in clinical practice. The limitations and invasiveness of conventional diagnostic modalities can hinder accurate diagnosis and management, causing patient discomfort. The convenient use of dermoscopy in these challenging locations has ushered in a new era for definitive diagnosis. Dermoscopy enables visualization of vascular structures and other subtle cutaneous features, opening up novel avenues in dermatologic morphology; moreover, the preservation of imaging data facilitates long-term follow-up and more in-depth research. While its advantages in atypical sites are undeniable, dermoscopy is not without the potential for false‑positive and false‑negative results. Although it cannot replace histopathologic biopsy, the combination of both approaches allows for a multidimensional, comprehensive assessment of the disease, holding promising prospects for clinical application.

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