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| REVIEW ARTICLE |
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| Year : 2020 | Volume
: 38
| Issue : 4 | Page : 205-216 |
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Dermoscopic manifestations of nail diseases
Sushmita Pradhan, Xin Ran, Siliang Xue, Yuping Ran
Department of Dermatovenereology, West China Hospital, Sichuan University, Chengdu, China
| Date of Submission | 01-Jan-2020 |
| Date of Decision | 17-Mar-2020 |
| Date of Acceptance | 21-Mar-2020 |
| Date of Web Publication | 16-Dec-2020 |
Correspondence Address:
Prof. Yuping Ran
Department of Dermatovenereology, West China Hospital, Sichuan University, No. 37, Guo Xue Xiang, Wuhou, Chengdu, Sichuan Province 610041
China
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/ds.ds_26_20
Nail dermoscopy in recent years has become an auxiliary noninvasive tool for the diagnosis of nail diseases. It detects the differentiating characteristics of the nail units and assesses in the management of nail diseases. Dermoscopy may not be a diagnostic tool for all nail diseases; however, it is very useful for early observation with high magnification. This article discusses the important and common dermoscopic manifestations of nail disease cases in the daily practice. Currently, the indications of dermoscopy include viral, bacterial, fungal, inflammatory, pigmented, traumatic nail diseases, nail tumors, and connective tissue disease.
Keywords: Beau line, connective tissue disease, dermoscopy, hand foot and mouth disease, nail lichen planus, nail pigmentation, nail psoriasis, nail tumors, onychomadesis, onychomycosis, paronychia, periungual warts, traumatic nails
How to cite this article:
Pradhan S, Ran X, Xue S, Ran Y. Dermoscopic manifestations of nail diseases. Dermatol Sin 2020;38:205-16 |
| Introduction | |  |
Dermoscopy of nails is an auxiliary method in the assessment of nail diseases. It is a simple yet very important diagnostic tool for physicians and nail surgeons. Dermoscopy makes the physical examinations of nails easier by helping to diagnose the disease that is insufficient with naked eyes avoiding preliminary misdiagnosis and sometimes biopsy. Different parts of the nail unit invisible to the naked eyes can be magnified and studied to conclude a probable diagnosis to guide the management and prognosis of different nail diseases. Nail dermoscopy is usually evaluated dry in the nail plate surfaces or matrix varying from lower to higher magnification. Dermoscopic observation can be performed using handheld dermatoscope or USB port connected videodermoscope. Nonpolarized dermoscopy allows us to evaluate the nail surface with detailed structural change. Polarized dermoscopy allows us to evaluate the nail unit deeper and avoid the reflectance of light to the nail surface. Ultraviolet (UV) dermoscopy show some special characteristics based on the density of absorbing nature of nail structure change. This article discusses the importance of the common dermoscopic manifestations of nail diseases in daily practice. Dermoscopic manifestations vary according to the characteristics of viral, bacterial, fungal, inflammatory, pigmented, traumatic nail diseases, nail tumors, and connective tissue disease. Even though dermoscopy may not be a diagnostic tool for some nail diseases, it may aid in the rapid abnormality detection of nail diseases.
| Dermoscopic Characteristics of Different Nail Diseases | | |
Viral disease
Hand, foot, and mouth disease
Hand, foot, and mouth disease is a common viral infection caused by Coxsackievirus A16 in children occurring during spring or autumn.[1] It is mainly characterized by vesicular eruptions in the palms, soles, oral cavity, and nail units. Dermoscopy of nail shows painless, noninflammatory condition with proximal shedding of the nail plate from nail matrix [Figure 1].[2] It indicates a sequelae of virus infection several weeks ago where the new nail begins to grow forward and forms a junction line with the separated damaged nail, and careful inquiry of the fever history could get the confirmed diagnosis. Beau lines appear as transverse ridges of the nail plate [Figure 2].[2] Onychomadesis may occur in severe systemic illness, infection, high fever, medications, nutritional deficiency, periungual inflammation, and trauma.[1] | Figure 1: (a) Cartoon illustration of onychomadesis. (b) Clinical feature of onychomadesis on the right thumb (patient). (c and d) Polarized dermoscopy of onychomadesis with proximal shedding (red asterisk) of the nail plate (blue arrows) from the nail matrix (×40)
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 | Figure 2: (a) Cartoon illustration of Beau line. (b) Clinical feature of Beau line on the right big toenail (patient). (c) Polarized dermoscopy of Beau line appearing as transverse ridges (yellow asterisks) of the nail plate (blue arrows) (×40)
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Periungual warts
Periungual warts can be seen both in fingernails and toenails. It is mostly caused by human papillomavirus 1, 2, and 4. Differential diagnosis of periungual warts is ungula Bowen disease and squamous cell carcinoma commonly presented with a verrucous lesion confirmed by histopathology.[3] Dermoscopy of periungual warts typically presents hyperkeratotic and rough lesions with micropapules and small black dots corresponding to dilated capillaries of the papillary dermis as cutaneous warts [Figure 3].[4] Dermoscopy may be useful in doubtful cases. | Figure 3: (a) Cartoon illustration of periungual warts. (b) Clinical feature of the periungual wart on the right fourth fingernail (patient). (c) Polarized dermoscopy of the periungual wart with hyperkeratotic and rough lesions (blue arrows); and red bleeding point (yellow asterisks) (×40)
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Fungal disease
Onychomycosis
Onychomycosis refers to the fungal infection of the nail bed and nail plate mainly caused by dermatophytes (Trichophyton spp., Microsporum spp., and Epidermophyton spp.), nondermatophyte mold and yeasts. Various dermoscopic patterns in onychomycosis are reported. Dermoscopy of distal subungual onychomycosis of the nail plate shows a jagged proximal border of the onycholytic area, with yellow-spikes projecting into the proximal dark yellow background nail plate, as well as the broken comb damage and hyperkeratosis at the far end [Figure 4].[5] Dermoscopy of superficial onychomycosis and proximal subungual onychomycosis of the nail plate shows white opaque friable patches irregularly distributed having KOH-positive [Figure 5].[6] Dermoscopy of subungual hyperkeratosis in the distal-free edges shows ruined appearance and collection of scales corresponding to fungal presence [Figure 6].[7] Yorulmaz and Yalcin reported the most common dermoscopic manifestations in 81 patients with onychomycosis was jagged-spike pattern of onycholysis in 52% followed by subungual ruin pattern and whitish patches (leukonychia).[8] In our experience, dermoscopy is diagnostics for onychomycosis. | Figure 4: (a) Cartoon illustration of distal subungual onychomycosis. (b) Clinical feature of distal subungual onychomycosis on the left big toenail (patient). (c and d) Polarized dermoscopy of distal subungual onychomycosis of the nail plate showing a jagged proximal border of the onycholytic area (red asterisk), with yellow-spikes (blue arrows) projecting into the proximal nail plate (×40)
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 | Figure 5: (a) Cartoon illustration of superficial and proximal subungual onychomycosis. (b) Clinical feature of superficial and proximal subungual onychomycosis on the right big toenail (patient). (c and d) Polarized dermoscopy of superficial and proximal subungual onychomycosis of the nail plate showing white opaque friable patches (red asterisks) irregularly distributed (blue arrows) having KOH-positive (×40)
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 | Figure 6: (a) Cartoon illustration of subungual hyperkeratosis. (b) Clinical feature of subungual hyperkeratosis on the right big toenail (patient). (c) Polarized dermoscopy of subungual hyperkeratosis in the distal free edges showing ruined appearance (blue arrows) and collection of scales (red asterisks) corresponding to fungal presence (×40)
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Bacterial infection
Paronychia is an inflammatory disease affecting the proximal and lateral nail folds mainly occurring as acute and chronic paronychia.
Acute paronychia
Acute paronychia is a nail infection due to bacterial penetration of the cuticle or the nail fold from direct or indirect trauma with inoculation of pathogens, mainly Staphylococcus aureus and ß-hemolytic Streptococcus.[9] It is presented with swelling, erythema, tenderness, throbbing, and pus formation.[10] Dermoscopy of acute paronychia shows erythematous pus discharge from proximal or lateral nail folds or uplifting of nail plate due to infection of the nail bed [Figure 7].[11] | Figure 7: (a) Cartoon illustration of acute paronychia. (b) Clinical feature of acute paronychia on the left fifth fingernail (patient). (c) Polarized dermoscopy of acute paronychia with erythematous pus discharge (blue arrows) from proximal or lateral nail folds or uplifting of nail plate due to infection of the nail bed (×40)
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Chronic paronychia
Chronic paronychia refers to the swelling of the proximal nail fold and the disappearance of the cuticle mainly caused by finger sucking in children.[12] Dermoscopy shows painful acute inflammation due to secondary colonization with Candida albicans and/or bacteria [Figure 8]. Chronic paronychia in proximal nail fold is caused by the irritative reaction, contact allergy, food hypersensitivity, Candida hypersensitivity, and true Candida paronychia.[11] | Figure 8: (a) Cartoon illustration of chronic paronychia. (b) Clinical feature of chronic paronychia on the left big toenail (patient). (c) Polarized dermoscopy of chronic paronychia with acute erythematous (yellow asterisk) inflammation (blue arrows) due to secondary colonization with Candida albicans and/or bacteria (×40)
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Inflammatory disease
Nail psoriasis
Nail psoriasis usually affects nail plate, nail bed, hyponychium, and nail matrix. Nail psoriasis is characterized by pitting, nail discoloration (salmon patch and oil drop), onycholysis, subungual hyperkeratosis, and splinter hemorrhage.[13] Pitting, crumbling, and leukonychia are involved in nail matrix; red spots in lunula; and onycholysis, oil spots, subungual hyperkeratosis and splinter hemorrhages are involved in nail bed.[14] Pitting are small punctuate depressions of the nail plate surface that results from defective keratinization of the foci of the cells of the proximal nail matrix commonly seen in psoriasis and alopecia areata.[4] Dermoscopy shows pitting as large, deep, and irregular in size, and distribution covered by large scales [Figure 9].[4] UV dermoscopy of pits shows light-green fluorescence [Figure 10]. Onycholysis in psoriatic fingernails is characterized by an erythematous border surrounding the distal edge of the detachment, by signs of nail bed inflammation, on dermoscopy shows bright yellow/white, slightly dented margin of the detachment [Figure 11].[4] Leukonychia of psoriatic nails is due to internal desquamation of keratinocytes that is unable to flake off because of the parakeratosis of the distal nail matrix.[15] Dermoscopy of leukonychia shows single or multiple opaque white irregular spots on the nail plate surface [Figure 12].[4] Nail discoloration, namely “oil drop” or “salmon patch” is characterized by a reddish yellow color on the nail bed like a drop of oil under the nail plate which is caused by parakeratosis and tightly arranged acanthosis under the nail plate.[13],[16] Dermoscopy of oil drop or salmon patch shows a circular translucent yellow-red area of discoloration in the middle of the nail of surrounding onycholysis [Figure 13].[4] Splinter hemorrhage can be seen as a small line with 3 mm length in the distal nail plate.[16] Dermoscopy of splinter hemorrhage shows the longitudinal orientation of the red lines allowing the observation of nail bed capillary dilations that precede rupture [Figure 14].[4] Subungual hyperkeratosis is characterized by the accumulation of scales under the nail plate, which is detached and uplifted due to excessive proliferation of nail bed/hyponychium keratinocytes.[4] Diffuse subungual hyperkeratosis is seen in psoriasis and distal subungual onychomycosis.[4] Dermoscopy of subungual hyperkeratosis in psoriasis shows accumulation of scales under the nail plate [Figure 15]. In a recent study done by Sari et al. showed pitting (58.8%), onycholysis (46.6%), Beau's line (46.6%), splinter hemorrhage (46.6%), salmon patch (33.3%), and subungual hyperkeratosis (33.3%) as the common dermoscopic findings in nail psoriasis.[17] They also found that dermoscopy cannot be replaced to histopathological examination as a diagnostic tool to nail psoriasis.[17] Yorulmaz and Artuz described “pseudo-fiber sign” as a new dermoscopic feature of nail psoriasis resembling red and black filamentous structures located along the cuticle, underneath the distal free edge on the hyponychium of nail plate detached areas suggested that it was related to nail bed psoriasis with bare capillaries.[18] | Figure 9: (a) Cartoon illustration of pitting in nail psoriasis. (b) Clinical feature of pitting on the right third fingernail (patient). (c) Nonpolarized dermoscopy of pitting in nail psoriasis with large, deep, and irregular pits in size (yellow asterisks), and distribution covered by large scales (×40)
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 | Figure 10: (a) Cartoon illustration of pitting in nail psoriasis. (b) Clinical feature of pitting on the left fourth fingernail (patient). (c) Polarized dermoscopy of pitting in nail psoriasis with large, deep and irregular pits in size (yellow asterisks) (×62). (d) Ultraviolet dermoscopy of pits (yellow asterisks) showing light-green fluorescence (×40)
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 | Figure 11: (a) Cartoon illustration of onycholysis in nail psoriasis. (b) Clinical feature of onycholysis on the right little fingernail (patient). (c) Polarized dermoscopy of onycholysis in nail psoriasis with bright white (red asterisks) slightly dented margin (blue arrows) of the detachment (×40)
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 | Figure 12: (a) Cartoon illustration of leukonychia in nail psoriasis. (b) Clinical feature of leukonychia on the left third toenail (patient). (c) Polarized dermoscopy of leukonychia in nail psoriasis with single or multiple opaque white irregular spots (red asterisks) on the nail plate surface (×40)
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 | Figure 13: (a) Cartoon illustration of oil spot or salmon patch in nail psoriasis. (b) Dermoscopy of oil spot or salmon patch on the left fourth fingernail with circular translucent yellow-red area (red asterisks) of discoloration surrounded by onycholysis (blue arrows) (×10)
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 | Figure 14: (a) Cartoon illustration of splinter hemorrhage in nail psoriasis. (b) Clinical feature of splinter hemorrhage on the left fourth fingernail (patient) (blue arrow). (c) Nonpolarized dermoscopy of splinter hemorrhage in nail psoriasis with the longitudinal orientation of the red lines (yellow asterisks) and allows observation of nail bed capillary dilations that precede rupture (×40)
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 | Figure 15: (a) Cartoon illustration of subungual hyperkeratosis of nail psoriasis. (b) Clinical feature of subungual hyperkeratosis on the right big toenail (patient). (c) Polarized dermoscopy of subungual hyperkeratosis in psoriasis with the accumulation of scales (red asterisks) under the nail plate, which is detached and uplifted (blue arrows) (×40)
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Nail lichen planus
Nail lichen planus is seen in 10% of the cases with lichen planus affecting fingernails than toenails.[19] The most common signs of nail lichen planus affecting nail plate are thinning, splitting, fissuring, longitudinal ridging, grooving, and atrophy. Dorsal pterygium is due to the irreversible damage to part of the nail matrix allowing adhesion of dorsum skin of the digit to the nail bed, forming a V-shaped extension of the proximal nail fold splitting the nail plate into two parts.[4] Dermoscopy shows formation from skin continuing with the skin of the proximal nail fold [Figure 16].[4] The color is pink red with elongated capillaries in early lesions.[4] Trachyonychia or “20-nail dystrophy” is characterized by a benign disease with rough nails-like sandpaper in a longitudinal direction. It can also be caused by psoriasis, lichen planus, or alopecia areata. Dermoscopy of the nail plate shows multiple fine and superficial longitudinal fissures covered by thin scales [Figure 17].[4] Longitudinal fissuring and distal splitting are the typical signs of nail matrix lichen planus where the nails are thinned showing longitudinal ridging and fissuring with distal splitting.[4] Dermoscopy shows multiple deep longitudinal fissures reaching the distal part of the nail as well as partial absence of the nail plate.[4] Dermoscopy is a useful diagnostic tool for therapeutic evaluation of the proximal nail plate to observe the emerging nail fold showing the regrowing of the nail plate in nail lichen planus.[4] In a study of dermoscopy of nail lichen planus done by Nakamura et al. showed abnormalities of the nail matrix with trachyonychia (40.51%), pitting (34.18%); anomalies of nail bed with chromonychia (55.7%), fragmentation of nail body (50.63%), splinter hemorrhage (35.44%), onycholysis (27.85%), subungual keratosis (7.59%); anomalies of nail matrix, bed and perionychial region with longitudinal streaks (82.28%), anonychia (1.27%); and paronychia (31.65%).[20] | Figure 16: (a) Car toon illustration of dorsal pterygium in nail lichen planus. (b) Clinical feature of dorsal pterygium on the left thumb (patient). (c) Polarized dermoscopy of dorsal pterygium in nail lichen planus with formation from skin continuing with the skin of proximal nail fold (yellow asterisks) forming “V” shaped (blue arrows) extension (×40)
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 | Figure 17: (a) Cartoon illustration of trachyonychia. (b) Clinical feature of trachyonychia on the right first fingernail (patient). (c) Nonpolarized dermoscopy of trachyonychia of nail lichen planus shows multiple fine and superficial longitudinal fissures (blue arrows) covered by thin scales (yellow asterisks) (×40)
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Nail pigmentation
Longitudinal melanonychia
Longitudinal melanonychia refers to the black-brown pigmentation of the nail due to the presence of melanin within the nail plate.[4] Longitudinal band starting from the proximal margin that extends to the distal margin involving the whole nail plate is called total melanonychia.[4] Longitudinal melanoma is present in 70% of the cases.[21] Nail melanoma is rare in Caucasian (1%–2% of melanomas), however, common in Asians (10%–20%) and Africans (25%).[21] Three important steps in evaluating melanonychia are to establish the pigment is melanin or not; to determine the development of melanonychia is due to activation or proliferation of matrix melanocytes, and; to assess if there is a proliferation to determine the disease is benign or malignant.[22] The ABCDEF rule for nail pigmentation[23] should be applied while using dermoscopy.[24] Dermoscopy of longitudinal melanonychia in children with low specificity suggest melanoma includes a brown background involving most of the nail plate with longitudinal brown to black lines with an irregular color, spacing, thickness, and abrupt ending [Figure 18].[25] Dermoscopy pattern for nevus shows brown background with longitudinal brown-black regular and parallel lines with regular spacing and thickness, whereas in children black dot due to pigment accumulation occurs in the nail plate.[4] Benati et al. identified three important dermoscopic pattern in nail band pigmentation that helped to distinguish a band from benign to malignant: width of the band, involving more than two-thirds of the nail plate in melanoma; presence of a gray-to-black color; and presence of nail dystrophy that increased the risk of nail melanoma detection three times more.[26] There lies high probability of diagnosis of nail melanoma in the presence of micro-Hutchinson sign indicating early or in situ lesions.[4] Micro-Hutchinson sign could be associated with a band of melanonychia or with amelanotic melanoma, characterized by the lack of melanin pigment [Figure 19].[4] Dermoscopy of nail melanoma suggest a brown-to-black background of the band with longitudinal lines irregular in their thickness, spacing, color, or parallelism where sometimes ABCDEF rule may not be applied with findings of irregular width or color observed in benign lesions [Figure 20].[27] Hirata et al. identified four intraoperative dermoscopic patterns: regular gray pattern typical for hypermelanosis, regular brown pattern typical for benign melanocytic hyperplasia, regular brown pattern with globules or blotches typical for melanocytic nevi, and an irregular pattern, typical for melanoma assisted in selecting best site for performing biopsy.[28] Although ABCDEF rule is applied in the dermoscopy of longitudinal melanonychia, histopathology is still a definitive method for nail pigmentation.[29] | Figure 18: (a) Car toon illustration of longitudinal melanonychia. (b) Clinical feature of longitudinal melanonychia on the right third fingernail (patient). (c and d) Polarized dermoscopy of longitudinal melanonychia with a brown background (yellow arrows) involving most of the nail plate with longitudinal brown to black lines (blue arrow) with an irregular color, spacing, thickness and abrupt ending (×40)
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 | Figure 19: (a) Cartoon illustration of longitudinal melanonychia with micro-Hutchinson sign. (b) Clinical feature of longitudinal melanonychia with micro-Hutchinson sign on the left fifth fingernail (patient). (c) Polarized dermoscopy of longitudinal melanonychia with micro-Hutchinson sign (yellow asterisks) (×40)
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 | Figure 20: (a) Cartoon illustration of melanoma. (b) Dermoscopy of melanoma on right first fingernail appearing as black pigmentation (white arrows). (×10)
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Green nail
Green nail is characterized by a green or black discoloration due to colonization by Pseudomonas aeruginosa producing a pigment named pyocyanin adhering to the irregular nail plate surface or located under an onycholytic nail plate.[30] Dermoscopy shows yellow-green discoloration and its localization [Figure 21]. Differential diagnosis consists of paronychia, onycholysis, and chemical exposures to solutions such as pyocyanin or pyoverdine.[31] | Figure 21: (a) Cartoon illustration of the green nail. (b) Dermoscopy of the green nail on a left thumb with yellow-green discoloration (red asterisks) and its localization (×10)
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Subungual hematoma
Subungual hematoma or subungual hemorrhages are a collection of blood in the space between the nail bed or matrix and the nail plate resulting from an acute painful injury or repetitive minor trauma to the nail apparatus.[32] Subungual melanoma or longitudinal melanonychia should be kept in the differential diagnosis as it can easily be misdiagnosed.[33] An acute subungual hematoma is easy to diagnose which explains the history of trauma. However, the chronic subungual hematoma is caused by repeated microtraumas where brown-black pigmentation of a toenail should be differentiated from melanotic pigmentation, i.e., from nail melanoma.[4] Dermoscopy shows the round shape of hematoma and its homogenous pigmentation [Figure 22]. The studies show that subungual hemorrhages exhibit a variety of colors upon dermoscopic examination. Ronger et al. first described the dermoscopic pattern of 22 cases of subungual hemorrhages by following terms: rounded proximal edge, purple-blue to brown color, and distal edges with a somewhat liner distortion.[24] Recently, Mun et al. studied 90 cases of subungual hemorrhages demonstrated the structures of blood spots in homogeneous pattern (n = 83, 92%), globular pattern (n = 38, 42%) and streaks (n = 35, 39%); peripheral fading (n = 49, 54%), periungual hemorrhages (n = 20, 22%) and destruction or dystrophy of the nail plate (n = 14, 16%).[34] They also exhibited a combination of more than one color in 84% of cases and only one color in 16% of cases.[34] | Figure 22: (a) Cartoon illustration of a subungual hematoma. (b) Clinical feature of the subungual hematoma on the right first fingernail (patient). (c) Polarized dermoscopy of subungual hematoma with homogenous pigmentation showing black (yellow asterisk) to red (white asterisk) areas, and the new developed normal nail line from proximal base (×40)
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Traumatic nail abnormalities
Traumatic onycholysis
Traumatic onycholysis is one of the most common toenail abnormalities consisting of bilateral and symmetrical. Dermoscopy of traumatic onycholysis shows a line of a detachment of the plate from the bed appearing linear, regular, and smooth surrounded by a normally pale pink bed without hyperkeratosis [Figure 23].[35] Meanwhile, secondary fungal infection as onychomycosis with brown to yellow-spikes might occur. Subungual space is usually whitish to yellow.[4] | Figure 23: (a) Cartoon illustration of traumatic onycholysis. (b) Clinical feature of traumatic onycholysis on the right second toenail (patient). (c) Polarized dermoscopy of traumatic onycholysis due to trauma with a detachment of the plate from the bed appearing linear, regular, and smooth (red asterisks) surrounded by a normally pale pink bed without hyperkeratosis (blue arrows). On the right-side, brown to yellow-spikes extending to proximal nail indicated onychomycosis (×40)
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Traumatic or frictional melanonychia
Traumatic or frictional melanonychia occurs in the fingernails of individuals who bite or traumatize the proximal nail fold and cuticle.[36] It may also appear in the fourth and fifth toenails which are exposed to chronic friction from the shoes. Dermoscopy of traumatic melanonychia shows a homogeneous gray pale brown or gray band [Figure 24]. | Figure 24: (a) Car toon illustration of traumatic or frictional melanonychia. (b) Clinical feature of traumatic or frictional melanonychia on the right fourth toenail (patient) (white arrow). (c) Polarized dermoscopy of traumatic or frictional melanonychia with a lateral homogeneous gray pale brown or gray band (yellow asterisk) (×10)
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Onychotillomania
Onychotillomania is a nail-picking disorder that is characterized clinically by general dystrophy and abnormal morphology of the nail plate, as well as damage to the nail bed and periungual skin.[23] Onychotillomania is commonly misdiagnosed and often confused with and treated as other nail disorders such as lichen planus, psoriasis, or onychomycosis.[37] Dermoscopy shows linear nail bed hemorrhages, periungual crusts, scales, hemorrhages, and wavy lines [Figure 25].[23] Maddy et al. evaluated dermoscopic features of 36 onychotillomania cases showed scales (n = 34, 94.4%), absence of nail plate (n = 30, 83.3%), wavy line (n = 25, 69.4%), hemorrhages (n = 23, 63.9%), crust (n = 22, 61.1.%), nail bed pigmentation (n = 17, 47.2%), speckled dots (n = 14, 38.9%), and nail plate melanonychia (n = 4, 11.1%).[23] They concluded that the absence of nail plate with multiple obliquely oriented nail bed hemorrhages, nail bed gray pigmentation, and presence of wavy lines were characteristic features of onychotillomania not observed in other nail diseases.[23] | Figure 25: (a) Cartoon illustration of onychotillomania. (b) Dermoscopy of onychotillomania on a right first fingernail with periungual crusts, scales and wavy lines (blue arrows) (×10)
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Nail tumors
Bowen disease
Bowen disease may affect periungual skin gradually destroying the nail plate. Dermoscopy of Bowen disease reveals dotted and/or glomerular vessels, islands of whitish scales, and hyperkeratotic, targetoid structures [Figure 26].[38] Dermoscopy of subungual Bowen disease also showed an inhomogeneous, blocky pigment streak fading toward the distal side.[39] Dermoscopy of woodgrain appearance of nail plate due to transepidermal elimination of tumor cell nests was also reported.[40] Brownish dots along the imaginary lines in pigmented Bowen disease has also been reported.[41] Longitudinal melanonychia may only be seen in some cases of Bowen disease. | Figure 26: (a) Cartoon illustration of Bowen disease. (b) Dermoscopy of the Bowen disease on the right thumb (patient) with hyperkeratotic, ruptured structure (red asterisks) (×10)
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Onychopapilloma
Onychopapilloma is a benign tumor arising from the distal matrix or proximal nail bed, including a band of longitudinal erythronychia, longitudinal leukonychia, longitudinal melanonychia or just splinter hemorrhages, with or without distal fissuring.[42] Dermoscopy shows a longitudinal red band, starting from the lunula and reaching to the distal margin, often associated with splinter hemorrhages [Figure 27].[4] Tosti et al. performed a dermoscopic study of 47 patients with onychopapilloma observed distal edge showing a keratotic subungual mass in correspondence to the streak and splinter hemorrhages as the only dermoscopic sign.[42] Onychopapilloma often shows a subungual filiform mass from the distal margin, whereas onychomatricoma shows characteristic features of multiple holes.[4] Dermoscopy of onychomatricoma shows honeycomb aspect of the distal part of the nail plate which is a diagnostic feature.[4] | Figure 27: (a) Cartoon illustration of onychopapilloma. (b) Dermoscopy of the onychopapilloma on the right thumb (patient) with longitudinal red band (yellow asterisk), starting from the lunula and reaching to the distal margin (blue arrows) (×10)
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Glomus tumor
Glomus tumor is a painful benign nail tumor mostly occurring in the subungual area of the hand (first and second fingernails) presenting approximately 1%–2% of all hand tumors.[43],[44] The classic triad of symptoms include intense paroxysmal pain, pinpoint tenderness, and cold sensitivity.[45] Dermoscopy of glomus tumor appears as an oval deep red-purple discolored area with blurred borders or a band of longitudinal erythronychia that does not usually reach the distal margin [Figure 28].[46] Intraoperative dermoscopy of the nail matrix and bed after nail plate removal before tumor excision aids in tumor localization and in visualization of the vascular pattern of the lesion appearing as ramified telangiectasis over a blue background suggesting the diagnosis of glomus tumor.[47] | Figure 28: (a) Cartoon illustration of glomus tumor. (b) Clinical feature of glomus tumor on the left thumb (patient). (c) Dermoscopy of glomus tumor with an oval deep red-purple discolored area (red asterisks) with blurred borders that do not usually reach the distal margin (×10)
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Pyogenic granuloma
Pyogenic granuloma is a benign vascular tumor that occurs in the periungual tissues, and nail bed mainly due to trauma, in growing nails, drugs appearing as a bleeding vascular nodule, peripheral nerve injury, and inflammatory disease.[48] Dermoscopy of pyogenic granuloma shows a vascular pattern with red color and milky-red veil and a regular pattern of the vessels [Figure 29].[4] The center of the lesion is red and darker, whereas the periphery is paler.[4] Brown color is seen with necrotic lesions.[4] Dermoscopy may not be diagnostic for pyogenic granuloma in cases of masses present on the nail bed which can be differentiated from squamous cell carcinoma and melanoma only through histopathological examination.[4] However, dermoscopy can be used to detect the masses on the lateral and proximal nail folds.[4] | Figure 29: (a) Car toon illustration of pyogenic granuloma. (b) Clinical feature of the pyogenic granuloma on the right fourth fingernail (patient). (c) Dermoscopy of pyogenic granuloma appearing as a vascular nodule (yellow asterisks) (×10)
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Connective tissue disease
Structural capillary abnormalities can be documented in periungual connective tissue diseases such as systemic sclerosis, dermatomyositis, mixed connective tissue disorder, Raynaud's phenomenon, and other systemic diseases.[49] Based on the severity of the connective tissue disease capillary abnormalities they can be classified as early changes (enlarged capillaries and hemorrhage), active disease (frequently enlarged capillaries and frequent hemorrhage), and late changes (irregular enlargement and severe loss of capillaries and avascular areas).[49] Dermoscopy of systemic lupus erythematous shows early nail fold hemorrhagic capillaries [Figure 30]. Dermoscopy of dermatomyositis shows active structural dilated capillary abnormalities also known as “scleroderma pattern” similar to systemic sclerosis [Figure 31].[49] | Figure 30: (a) Cartoon illustration of systemic lupus erythematous. (b) Clinical feature of the systemic lupus erythematous on the right first fingernail (patient). (c) Polarized dermoscopy of systemic lupus erythematous appearing as early nail fold hemorrhagic capillaries (blue arrows) (×40)
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 | Figure 31: (a) Cartoon illustration of dermatomyositis. (b) Clinical feature of the dermatomyositis on the right middle fingernail (patient). (c) Polarized dermoscopy of dermatomyositis appearing as active proximal dilated capillaries (blue arrows) (×40)
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| Conclusion | | |
This review demonstrates the importance of nail units' dermoscopy affecting the subungual regions rapidly assisting in the diagnosis of various nail diseases in daily practices. Distinctive dermoscopic signs of various nail diseases have also been described and allowed a differential diagnosis [Table 1]. Its importance must be taken into consideration in cases of doubtful diagnosis before histopathological examinations. Further studies may help clarify the importance of recent advances of dermoscopy in nail diseases. Nevertheless, it is important for general practitioners and dermatologists to be able to diagnose nail diseases using dermoscopy.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19], [Figure 20], [Figure 21], [Figure 22], [Figure 23], [Figure 24], [Figure 25], [Figure 26], [Figure 27], [Figure 28], [Figure 29], [Figure 30], [Figure 31]
[Table 1]
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