Dermoscopy of nonpigmented nail lesions

INTRODUCTION — Nail dermoscopy, also known as onychoscopy, is a useful technique that complements the clinical examination in the evaluation of numerous nail conditions, including nail pigmentations; melanocytic and nonmelanocytic nail tumors; and inflammatory, traumatic, and infectious disorders [1].

This topic will discuss the dermoscopic features of nonpigmented nail lesions. The dermoscopic features of nail pigmentations are discussed separately. Nail disorders are also discussed separately. (See "Dermoscopy of nail pigmentations" and "Overview of nail disorders".)

TECHNIQUE — The dermoscopic examination of the nail plate and periungual tissues can be performed using both polarized and nonpolarized instruments. (See "Overview of dermoscopy", section on 'Types of dermatoscopes'.)

Nonpolarized contact dermoscopy of the nail plate requires the use of ultrasound gel as an interface medium, as it allows a better contact with the convex nail surface. For the examination of the free nail edge, gel or alcohol can be used as the interface medium. Alcohol is suitable for the evaluation of the proximal and lateral nail folds and hyponychium.

Areas to be examined include the nail plate, the nail plate free edge, the hyponychium, and the nail folds (picture 1 and figure 1). Dermoscopy can also be utilized intraoperatively to assess the morphology and margins of the lesion and optimize excision. Intraoperative dermoscopy is usually performed with polarized instruments.

NONMELANOCYTIC NAIL TUMORS — In the evaluation of nonpigmented lesions suspicious for nail unit tumors, the dermoscopic examination of the nail plate may provide important clues to the diagnosis. The examination of the nail plate free margin is of particular value for the diagnosis of uncommon nail tumors such as onychomatricoma and onychopapilloma.

Onychomatricoma — Onychomatricoma is a benign fibroepithelial tumor that originates in the nail matrix and penetrates the nail plate with multiple digitations. Clinical examination reveals a thickened yellowish or pigmented nail plate with transverse over-curvature and multiple holes at the free margin (picture 2A-B) [2]. (See "Overview of nail disorders", section on 'Onychomatricoma'.)

Nail plate dermoscopy shows longitudinal, parallel white lines that correspond to the tumor digitations within the nail plate (picture 3). Splinter hemorrhages are very common and may affect the proximal nail plate. Distal edge dermoscopy showing woodworm-like cavities of the distal free edge (picture 4) is pathognomic. In a series of 34 cases of onychomatricoma, the preoperative diagnosis was suggested by the presence of parallel white lines and sharp lateral demarcation of the lesion at nail plate dermoscopy [3]. In this study, the authors describe the woodworm cavities at the free edge as dark dots and pitting.

Onychomycosis may occur in association with onychomatricoma, as fungi can easily penetrate the channels within the nail plate. In these cases, dermoscopy of the nail plate will show the typical features of onychomatricoma, whereas dermoscopy of the distal free edge reveals a "ruin appearance" of subungual keratosis usually seen in onychomycosis [4].

Glomus tumor — Glomus tumor (picture 5A-C) is a benign tumor of the glomus body that most frequently develops in the subungual areas of the hand, representing approximately 1 to 2 percent of all hand tumors [5,6]. It usually occurs in adult and middle-aged individuals, predominantly in women. Paroxysmal pain in the fingertips, tenderness, and cold intolerance are typical initial symptoms and may occur before the lesion is evident at clinical inspection.

On dermoscopic examination of the nail plate, glomus tumor appears as an irregular, red or purple spot with small telangiectasias (picture 6) [7]. The examination of the nail free edge may show a red hue in the lesion (picture 7). On ultraviolet light dermoscopy, glomus tumor shows a characteristic "pink glow," which denotes the vascular nature of the tumor [8]. (See "Overview of benign lesions of the skin", section on 'Glomus tumor'.)

Digital myxoid cysts — Digital myxoid cysts (DMCs), also called digital mucous cysts, most commonly involve the distal interphalangeal joint or the proximal nail fold but can occasionally have a subungual location. DMCs result from a leakage of synovial fluid through a breach in the joint capsule. Dermoscopy is useful to detect the keratotic plug that corresponds to the cyst opening and indicates the cyst location (picture 8) [9]. (See "Overview of benign lesions of the skin", section on 'Digital myxoid cyst'.)

Onychopapilloma — Onychopapilloma is a benign tumor of the nail bed and distal matrix. It usually presents as longitudinal erythronychia and, less commonly, as longitudinal leukonychia, longitudinal melanonychia, or just splinter hemorrhages, with or without distal fissuring [10].

Dermoscopy of the nail plate shows a pale band with single or double splinter hemorrhages; examination of the free edge is diagnostic and shows a characteristic subungual keratotic mass, which may contain hemorrhagic vessels (picture 9A-B). (See "Overview of nail disorders", section on 'Onychopapilloma'.)

Pyogenic granuloma — Pyogenic granuloma is a relatively common, benign vascular tumor that frequently involves the nail unit, including the periungual tissues and nail bed. The dermoscopic examination of the lesion shows a reddish homogeneous area, often with a white collarette at the periphery. White lines similar to a double rail may intersect older lesions. Differentiating pyogenic granuloma from amelanotic melanoma can be difficult as they may have very similar dermoscopic features. (See "Pyogenic granuloma (lobular capillary hemangioma)".)

Warts — Warts are the most common nail tumor. They predominantly affect children and young adults. Periungual warts are usually caused by human papillomavirus 1, 2, and 4. Maceration and trauma, especially nail biting, are favoring factors.

Warts of the nail folds usually present as periungual hyperkeratotic lesions. Although in most cases the diagnosis is clinically obvious, dermoscopy may be useful to confirm diagnosis in doubtful cases. Lesions show a typical rough surface with black to red dots and globules corresponding to dilated capillaries, as seen in cutaneous warts (picture 10). (See "Cutaneous warts (common, plantar, and flat warts)".)

Bowen disease and squamous cell carcinoma — Bowen disease and squamous cell carcinoma may affect the periungual skin and gradually destroy the nail plate. Melanonychia due to melanocyte activation may occur. The diagnosis is often delayed, since these lesions are commonly misdiagnosed as warts. (See "Overview of nail disorders", section on 'Squamous cell carcinoma'.)

Dermoscopy of Bowen disease shows dotted and/or glomerular vessels, islands of whitish scales, and hyperkeratotic, targetoid structures (picture 11) [11]. White circles can be seen in squamous cell carcinoma.

In some patients, longitudinal melanonychia may be the only manifestation of Bowen disease. In a reported case, dermoscopy showed an inhomogeneous, blocky pigment streak that faded in color toward the distal side [12]. Pigmented Bowen disease presenting with brownish dots along imaginary lines has also been reported [13].

DIFFERENTIAL DIAGNOSIS OF ONYCHOLYSIS — The term onycholysis describes the detachment of the nail plate from the nail bed. It can be caused by a wide range of nail disorders, including inflammatory diseases (eg, psoriasis, lichen planus), bacterial or fungal infections, subungual tumors, and trauma. Dermoscopy may be helpful in the differential diagnosis of onycholysis, both in fingernails and toenails.

Onycholysis of the fingernails

Psoriatic onycholysis — The diagnosis of psoriasis can be difficult in patients in whom onycholysis (picture 12) is the only clinical manifestation of the disease. In these cases, the dermoscopic examination of the hyponychium can provide valuable clues to the diagnosis, such as the presence of irregularly distributed, dilated, tortuous, elongated capillaries that resemble those seen in scalp psoriasis or in cutaneous psoriatic plaques. The number of vessels is positively correlated with disease severity and response to treatment. Magnification of at least 40 times is required to visualize twisted capillaries, which otherwise appear as red dots on low magnification (picture 13) [14]. (See "Nail psoriasis".)

Hemorrhagic onycholysis — The presence of a large number of splinter hemorrhages within the onycholytic area suggests drug-induced onycholysis, as seen in photo-onycholysis or onycholysis from taxanes (picture 14). Although a few splinter hemorrhages can be seen in onycholysis associated with eczema, psoriasis, or onychomycosis, a large number of splinter hemorrhages and blood suffusion of the onycholytic area are typical of drugs.

Pseudomonas colonization — Pseudomonas colonization is a common complication of onycholysis, regardless of its cause. The presence of a bright green color at dermoscopy is typical (picture 15).

Onycholysis of the toenails

Onychomycosis — In distal subungual onychomycosis, dermoscopy of the nail plate reveals a jagged proximal border of the onycholytic area, with yellow-white spikes projecting into the proximal nail plate (picture 16) [15]. Examination of the distal free edge shows subungual hyperkeratosis with a ruined appearance (picture 17) [16].

Dermoscopy can also be helpful in selecting the area to sample for mycologic examination, as it visualizes yellow streaks and patches, where fungi are more abundant (picture 17) [17]. (See "Onychomycosis: Epidemiology, clinical features, and diagnosis".)

Traumatic onycholysis — Traumatic onycholysis is one of the most common toenail lesions. On dermoscopy, the shape of the proximal border of the onycholytic area allows the differentiation of traumatic onycholysis from onychomycosis. A linear, sharp proximal border suggests traumatic onycholysis (picture 18). The presence of small hemorrhages within the onycholytic area is an additional clue to the diagnosis.

SELF-INDUCED NAIL DISORDERS — Onychotillomania is a common nail disorder, although frequently misdiagnosed and underreported [18]. Repeated nail manipulation causes nonspecific, varied, and bizarre findings that are not specific. Dermoscopy typically shows linear nail bed hemorrhages, periungual crusts, scales, and hemorrhages; melanonychia due to melanocyte activation is common (picture 19A-B). (See "Skin picking (excoriation) disorder and related disorders", section on 'Nail picking disorder'.)

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

●Dermoscopy is a useful tool in the evaluation of all nail disorders. Although in many cases dermoscopy simply enhances features that are already visible with the naked eye, it may be of invaluable help in the diagnosis of a number of nail conditions, including benign and malignant tumors, inflammatory disorders, and trauma. (See 'Introduction' above and 'Technique' above.)

●In the evaluation of lesions suspicious for nail unit tumors, the examination of the nail plate and, in particular, of the nail free edge under a dermatoscope often provides important clues to the diagnosis. (See 'Nonmelanocytic nail tumors' above.)

●Dermoscopy is also useful in the differential diagnosis of onycholysis, a nonspecific nail lesion that can be caused by inflammatory diseases, bacterial and fungal nail infections, and trauma. (See 'Differential diagnosis of onycholysis' above.)