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Differentiating Nail Diseases With Dermoscopy

The precise use of dermoscopy can make a difference in getting an accurate diagnosis of nail disease. This author offers practical pearls in using dermoscopy to get a clear clinical picture of conditions including nail pigmentation and onychomycosis.

Dermoscopy, a non-invasive technique that allows the magnification of lesions not visible to the naked eye, was originally for the evaluation of pigmented lesions. Its use has expanded to the evaluation of inflammatory skin conditions, non-pigmented lesions like warts, and hair and nail disorders. As podiatric physicians, the use of dermoscopy for nail disorders is a practice enhancer.  

Before delving into the specifics of nail diseases and dermoscopy, it is relevant to discuss the basics of a dermatoscope. Most physicians use a handheld device that they can keep in a coat pocket or attach to a smartphone.

A dermatoscope is much more complex than a simple magnifying glass; it is a magnification lens (generally 10 x magnification) with polarized lights placed circumferentially that allow for visualization of sub-surface structures, patterns and colors that are not visible clinically.1 The devices with polarized lights allow for dry dermoscopy, or the lack of using a liquid interface (such as ultrasound gel or alcohol based hand sanitizer) as in immersion dermoscopy. If there is no contact between the dermatoscope’s lens and the skin/nail lesion, then one does not have to cleanse the lens in between uses. Both dry and immersion dermoscopy can evaluate nails and there are devices that allow the use of both types of dermoscopy. The devices themselves do not take photographs but do have attachments that allow one to use the devices with a smartphone or digital camera.

The use of the dermatoscope during the skin/nail evaluation is part of the routine exam and is not an extra procedure or billable service. Once the practitioner has mastered the technique of using the dermatoscope and feels comfortable utilizing it during the exam, it is an evaluation that takes seconds to do and can greatly enhance decision-making. This decision-making aspect is incredibly useful with nail disorders. Since most nail disease is onychomycosis, the remainder can range from psoriasis to nail dystrophy secondary to biomechanics and beyond.

Nail dermoscopy or onychoscopy can evaluate pigmented streaks in nails to onychomycosis.2 According to Piraccini and colleagues, nail dermoscopy can visualize common findings of certain nail diseases, reinforce a diagnosis, and guide the management of the nail issue.2 One may begin evaluating the nail using dry dermoscopy and then can switch to using a liquid interface to analyze the nail plate further as well as analyze the distal and proximal nail areas.  

This article aims to distinguish various toenail issues using a dermatoscope and how it is an important first step in determining course of action.  

Evaluating Pigmentation Of The Nail Unit

The original purpose of dermoscopy was in distinguishing skin lesions as either melanocytic or non-melanocytic. We can apply the same to pigmentation of the nail unit. Dermoscopy can be useful in determining if there is a subungual hematoma or surface staining (following dye or nail polish use) versus a benign nevus originating at the nail matrix. A nevus may be visible as a longitudinal melanonychia described as brown to black to gray discoloration in the nail unit. In certain populations, this will be a common and natural variation, but in the Caucasian adult population, consider this malignant until proven otherwise. A dermatoscope allows evaluation of the longitudinal melanonychia and prevents an unnecessary biopsy of a benign nail pigmentation no matter the patient population.

Consider three points when performing a dermoscopic evaluation of nails for pigmentation: 1) Is the pigmentation melanocytic in origin? 2) If it is melanocytic, is the pigmentation a result of melanocyte activation or proliferation in the nail matrix? 3) If the pigmentation results from proliferation, is it benign or malignant?2  

The pigmentation resulting from a subungual hematoma is often a concern for patients. In some cases, patients may remember the inciting trauma, or may not have felt the restriction of a tight toe-box in the case of diabetic neuropathy. Either way, the resulting black to brown color may alert the patient or primary care physician. Using the dermatoscope, one can quickly diagnose a subungual hematoma, a non-melanocytic lesion, due to its distinguishing characteristics: the pigmentation appears red to brown to purple, often with a homogeneous patch and globules at the proximal edge with a more linear pattern at the distal edge.2 Of course, if the hematoma does not progress distally with time, there needs to be further evaluation.  

Green pigmentation is often indicative of a Pseudomonas aeruginosa colonization. The organism produces a pigment called pyocyanin, which adheres to the nail plate or the nail bed (in the cases where there is onycholysis).2 Application of the dermatoscope will yield a bright green color that fades to yellow in the periphery. This pigmentation also does not start from the nail matrix, and debridement of the onycholytic nail plate will allow an even more impressive evaluation of the color.  

Longitudinal melanonychia, or the pigmented dark streaks in nails, can be present for a variety of reasons: origins that are fungal, endocrine in nature, medication-induced, or due to melanocyte activation or proliferation. Many physicians and patients have noticed that pigmented streaks that are fungal in origin resolve when patients use oral or topical antifungal medication. If this occurs, then the streak was due to Trichophyton rubrum var. melanoides or by another fungi.2 Dermoscopy of these lesions reveals a multicolor (yellow, gray, black, red) streak that is wider at the distal end than the proximal and is homogeneous. Further evaluation of the nail is warranted to inspect for other signs of nail mycosis, which I will discuss elsewhere in this article.  

Determining If The Nail Has Melanocyte Activation Or Proliferation

If nail pigmentation is melanocytic in nature rather than due to a fungal or a systemic cause, one must determine melanocytic activation versus proliferation. Present pigmentation has been deposited months to weeks earlier, but dermoscopy is a first step beyond a history and physical examination to determine the next step.3

Before applying the dermatoscope to the lesion, it is important to ask the patient how long the streak has been present, if it has changed, how many digits are involved, and if there is any personal or family history of skin cancer or nail pigmentations. After this, apply the dermatoscope to the distal tip or free edge of the nail plate and observe if the pigment is present in the lower (deeper) part or the superficial (dorsal) aspect of the nail plate. If it is in the lower part of the nail plate, it is most likely originating in the distal nail matrix in comparison to pigmentation located in the dorsum of the nail plate is most likely originating in the proximal nail matrix.2 Next, determine if the pigmented lines on the dorsum of the nail plate are have homogeneous color, are a few millimeters wide, are parallel and continuous, and have well-defined borders.  

Armed with this information, the physician should determine if melanocyte activation or proliferation is present. Melanocyte activation will appear as homogeneous, thin, longitudinal gray lines with regular borders.2 This may be visible on multiple nails in adults and children. Melanocyte proliferation, which when benign is known as a nevus of the nail matrix, presents as a brown background with parallel lines of even color and width in adults.

In children, melanocyte proliferation may present as a brown background with lines that have “different color and irregular width.”2 With children and nail pigmentation, the rules of dermoscopy for adults do not apply and dermoscopy for pediatric patients is beyond the scope of this article.   

In contrast, melanocytic proliferation that is malignant (nail matrix melanoma, a form of acral melanoma), appears as a brown background with longitudinal lines that are “irregular in color, width, and parallelism.”2 This commonly occurs on one digit (in order of frequency: thumb, hallux, index finger) and the pigmentation is rapidly enlarging and multicolored. This occurs in adults. From an algorithm standpoint, in an adult patient, first determine the history of the pigmentation, then examine the nail and periungual tissue for pigmentation visible to the naked eye. Apply the dermatoscope and view the nail plate as well as the periungual tissue for any pigmentation leaking onto the periungual skin (known as micro-Hutchinson’s sign and Hutchinson’s sign).

If the lesion meets the above criteria for malignant melanocytic proliferation or if there is any ulceration of the nail bed, a biopsy of the nail unit is warranted.2 If dermoscopy of the nail plate is confusing or doesn’t fit the patterns as described, then a histopathologic confirmation is also warranted.  

How Dermoscopy Can Distinguish Onychomycosis From Other Nail Conditions

Dermoscopy of the nail unit is useful as a first step in distinguishing onychomycosis from traumatic onycholysis from nail dystrophy secondary to a biomechanical cause.

Onycholysis, or a separation of the nail plate from the nail bed, may affect the nails in a bilateral and symmetrical pattern and have no pain associated with it. Under the dermatoscope, the border of onycholysis may be smooth and regular, with the distal nail plate appearing white from the air in that pocket.2 From a nail dystrophy perspective, onycholysis and discoloration are often present in a hammered, mallet or adductovarus digit. In nails affected by these digital deformities, dermoscopy of the onycholysis and patches is necessary, followed by an evaluation of the dermoscopic patterns of onychomycosis are present.  

Onycholysis is an early sign in distal subungual onychomycosis and may be visible in one or both hallux toenails. Onycholysis commonly presents in this subtype as whitish spikes that start distally and point towards the proximal nail fold. These spikes most likely represent the path of dermatophyte invasion from the hyponychium to the proximal aspect of the nail unit. It may also present as a white-yellow discoloration or as a multicolor parallel banded area called the aurora borealis pattern.4 From the distal tip of the nail, the dermatoscope will reveal a “ruin” appearance in which the subungual debris creates a cave or cavern-like appearance that is distinctive of a mycotic nail.5

Yorulmaz and Yalcin studied 81 patients with onychomycosis to determine the most common patterns via dermoscopy.6 They confirmed that the jagged spike pattern of onycholysis was present almost 52 percent of the time, followed by the subungual ruin pattern and whitish patches (leukonychia).

If the clinician suspects white superficial onychomycosis, it is best to evaluate the nail plate via dry dermoscopy to better observe the white, friable patches as immersion dermoscopy would mask these areas. Also, if the patient wears nail polish, dermoscopy helps visualize superficial staining from a nail varnish versus the discoloration visible in onychomycosis. After dermoscopic evaluation, the clinician can then choose his or her lab test of choice to confirm the presence of dermatophytes to further create a treatment plan.  

From a clinical perspective, onychomycosis and nail psoriasis can be indistinguishable. Onycholysis is also highly present in affected psoriatic nails, but more so on the fingernails than the toenails. That said, the proximal border of onycholysis in psoriatic nails looks pink clinically, but dermoscopy reveals a yellow-orange color.2 Application of the dermatoscope to the hyponychium of affected nails in these patients will show tortuous dilated capillaries.7  

Final Thoughts

Onychoscopy or any type of dermatoscopic evaluation is useful to make and refine diagnoses. However, it is a technique that takes time and practice to learn. The best way to start using the dermatoscope is use it to evaluate as many patients as possible while confirming your findings with pictures from articles, texts and helpful blogs that exist to help the motivated self-learning clinician. Following a solid history and physical exam, the clinician can follow the algorithm of: evaluate the nail unit clinically, apply the dermatoscope and try to determine the source of the pigmentation.

Keep in mind that nail pigmentation may be an extension of dermatophyte infection, systemic medical issues, medications, trauma, or a natural variation. If the pigmentation is gray, melanocyte activation is likely present. If the pigmentation is brown-black, melanocyte proliferation is present and we must further classify it as benign or malignant.

Routine use of this tool will yield information that will direct the course of the office visit. In the end, you will have a satisfied patient who can walk out of your office with an idea of the nail diagnosis and ultimately, a treatment plan.

Dr. Vlahovic is a Clinical Professor in the Department of Podiatric Medicine at Temple University School of Podiatric Medicine.

References

1.    Micali G and Lacarrubba F. Dermatoscopy instrumental update. Dermatol Clin. 2018; 36(4):345–348.
2.    Piraccini BM, Alessandrini A, Starace M. Onychoscopy dermoscopy of the nails. Dermatol Clin. 36(4):431–438.
3.    Hirata SH, Yamada S, Almeida FA, et al. Dermoscopy of the nail bed and matrix to assess melanonychia striata. J Am Acad Dermatol. 2005;53(5):  884–6.
4.    De Crignis G, Valgas N, Rezende P, et al. Dermatoscopy of onychomycosis. Int J Dermatol. 2014;53(2):e97–9.
5.    Kaynak E, Goktay F, Gunes P, et al. The role of dermoscopy in the diagnosis of distal lateral subungual onychomycosis. Arch Dermatol Res. 2018; 310(1):57–69.
6.    Yorulmaz A, Yalcin B. Dermoscopy as a first step in the diagnosis of onychomycosis. Adv Dermatol Allergol. 2018; 35(3):251–258.
7.    Grover C, Jakhar D. Onychoscopy: A practical guide. Indian J Dermatol Venereol Leprol. 2017;83(5):536-49.

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By Tracey C. Vlahovic, DPM, FFPM RCPS (Glasg)
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