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Can Dermoscopy Be Beneficial For Point Of Care Diagnosis Of Onychomycosis?

Onychomycosis is one of the most frequent pathologies presenting in podiatry practices. However, at times, more subtle differences in the clinical presentation may delay an accurate diagnosis and timely treatment. Accordingly, this author discusses the technique and benefits of using a dermatoscope to improve patient care of this common disorder. 

As podiatric physicians, we feel confident in diagnosing toenail onychomycosis clinically due to the vast number of cases we see daily in the office. However, one may have second thoughts about that ability or feel frustrated by the lack of clinical correlation after the return of a few negative clinical laboratory tests such as periodic acid Schiff stain (PAS), KOH and fungal culture, or polymerase chain reaction (PCR) testing. 

Explanations for a negative fungal test might include the area of the nail unit one samples and its influence on the chosen test as well as the numerous differential diagnoses that are visually identical to onychomycosis. A dermatoscope is a tool that allows one to provide both point-of-care diagnosis and formulate a stronger differential diagnosis while waiting for the fungal test results to return. 

The development of dermoscopy, or the use of a device that provides non-invasive handheld imaging, was originally intended to assess pigmented lesions on the skin and the potential need for biopsy. Over the years, dermatologists have utilized dermoscopy in areas beyond assessing pigmented lesions such as diagnosing inflammatory skin disorders, hair issues and nail disease. Considering that onychomycosis constitutes 50 percent of the nail disease that physicians see in the office, having a device that takes some of the guesswork out of the equation is practical and cost-efficient.1 

From the clinical perspective, the average dystrophic nail may visually be equivalent to onychomycosis but a different world emerges with the use of a dermatoscope. For instance, dermoscopy can assist in determining if the nail dystrophy is trauma-related (like from a sport that has hard stops like basketball), surface staining from nail polish or a sock, or even a benign nail matrix tumor known as an onychomatricoma. 

In general, what are the clinical characteristics of onychomycosis? Findings include yellow to white to brown discoloration (chromonychia), onycholysis (separation of the nail bed from the nail plate), subungual debris, geographical disturbances of the nail plate surface (Beau’s lines, onychorrhexis, pitting), brittleness and subungual hematoma. These findings are not unique to onychomycosis and can appear with other nail pathologies. When the clinician uses a dermatoscope, he or she can magnify these findings, which provides a rapid way to confirm suspicion of onychomycosis and pursue subsequent clinical lab testing to ensure the correct diagnosis. 

Applying A Dermatoscope To The Nail Unit 

Most dermatoscopes fit into a clinician’s pocket and can attach to a smartphone in order to take photos and/or visualize it on a larger screen. However, as the nail plate is a convex surface, it may cause a learning curve for the practitioner to apply the dermatoscope to the nail and obtain the focus of the pathology. 

In order to visualize the nail plate clearly, I first apply the dermatoscope to a dry nail without contacting the surface directly. However, if I want to examine the distal nail edge or the proximal nail fold, I apply either ultrasound gel or hand sanitizer as an interface between the nail and the scope to visualize deeper structures. I use a dermatoscope that provides 10x magnification and is considered a “hybrid” as it has both polarized light and non-polarized light illumination capabilities. This allows me to use an interface gel if I desire or provide non-contact dermoscopy. 

Most of the time, I use non-contact, polarized light dermoscopy for the toenails. I apply the scope about one to two cm above the area in question and then place my eye a few centimeters above the scope until the field appears in focus. I also examine the distal nail plate in addition to the dorsal nail plate. For example, the longitudinal white lines that we often see with onychomycosis on the dorsal surface of the nail plate can provide confirmation (when you view them from the distal nail) that a benign tumor from the nail matrix is present (onychomatricoma). I can then repeat the dermatoscope nail exam by attaching my scope to my smartphone via a magnetic phone case and taking photos to show the patient the pathology in question, and upload those images in the electronic medical record. 

Understanding The Evidence On Dermatoscopic Findings Of Onychomycosis 

Various authors have correlated onychomycosis-related patterns with the dermatoscope and a positive fungal test (KOH, culture, PAS, Gomori methenamine silver (GMS)). For the purposes of this article, I will focus on distal subungual onychomycosis dermoscopy findings only as that is the most frequent type of onychomycosis we see. 

Piraccini and colleagues were the first to describe the patterns of distal subungual onychomycosis in comparison to traumatic onycholysis via dermoscopy.2 Since traumatic onycholysis and onychomycosis can be virtually impossible to distinguish without mycological tests, this study aimed to define the dermatoscopic characteristics of the 57 patients who had dermoscopy, clinical photography and mycological testing (KOH and culture) of their affected great toenail. For distal subungual onychomycosis specimens, the most specific dermatoscopic patterns that the study authors saw were the “jagged edge with spikes” and “longitudinal striae.” 

The jagged edge with spikes pattern describes a serrated knife-like edge appearance of white streaks at the tip of the onycholysis pointing toward the proximal nail fold. Longitudinal striae are white to yellow finger-like projections that also point toward the proximal nail. The study authors also reported blackish globules that were subungual hemorrhages in nails with distal subungual onychomycosis, but this finding was not as specific as the two aforementioned patterns.2 The authors were also the first to coin the “aurora” pattern term, which describes the pigmentation produced in linear figures reminiscent of the aurora borealis phenomenon. In comparison to the distal subungual onychomycotic nails, the investigators noted linear edges of white discoloration in specific traumatic onycholysis 100 percent of the time.2 

Kaynak and team reported the frequency of dermatoscopic findings in onychomycosis that were confirmed to be distal subungual onychomycosis by either PAS or hematoxylin and eosin (H&E) stain/fungal culture in 97 patients.3 Unlike the work by Piraccini and colleagues, Kaynak and coworkers did not observe as high a frequency of the jagged edge pattern. Their laboratory confirmation of the following patterns they saw with the dermatoscope yielded a high diagnostic sensitivity of distal subungual onychomycosis. “The ruin appearance” and various manifestations of leukonychia were their highest-rated dermatoscopic patterns that correlated to distal subungual onychomycosis. The ruin appearance describes the visual appearance of the subungual debris and its ability to affect the underside of the nail plate. 

Subungual debris is the skin’s inflammatory reaction pattern to the process of fungal invasion. One can best view this by positioning the dermatoscope at the distal edge of the nail plate. Leukonychia or white discoloration may appear on the nail plate in a punctate (spots), homogeneous (discrete areas) or longitudinal (thin streaks) fashion. These patterns are thought to correlate with the presence of the fungus in the ventral surface of the nail plate. In addition, Kaynak and colleagues observed the distal irregular termination pattern, which presents as an irregular and crumbly nail plate edge at the hyponychium.3 While one can obviously see this clinically, a dermatoscopic view gives the clinician a whole new appreciation for the dryness and brittleness of the nail plate distally. 

The findings of Yorulmaz and Yalcin, who only utilized KOH as their means of mycologic testing, correlated with the findings of in the studies of Piraccini and Kaynak and their respective coauthors.2-4 Their study of 81 patients with onychomycosis had consistent patterns of jagged edges with spikes, longitudinal streaks, subungual hyperkeratosis (ruin appearance) and leukonychia. The consistent longitudinal patterns speak to the anatomy of the nail unit. The nail plate has longitudinal rete ridges that fit into the ridges of the nail bed.4 In distal subungual onychomycosis, the fungal invasion advances from the hyponychium distally and travels proximally. The hyponychium serves as a weak barrier between the world and the nail unit, which dermatophytes exploit. The weak adhesions at the hyponychium are of little concern as the fungus metabolizes keratin and colonizes the nail unit while following the linear pattern created by the longitudinal rete ridges.4 

Practitioners can also see another anomaly of onychomycosis, the dermatophytoma, both clinically and via the dermatoscope. A dermatophytoma is an amalgamation of hyphae and scales, and appears as a distinct yellow to brown digitation in the nail plate.5 With the dermatoscope, the dermatophytoma appears as a “homogeneous, matte, yellow-orange discoloration” subungually and connects to the distal margin of the nail by a linear yellow-white band.5 

Personally, I use the dermatoscopic patterns of distal subungual onychomycosis to help me determine which nails to sample for mycologic testing. Once I have observed one or more of the patterns described above, I focus on that nail to retrieve as much proximal subungual debris as possible to provide a better sample for fungal culture or PAS, polymerase chain reaction, etc. 

Differentiating Distal Subungual Onychomycosis From Other Nail Diseases 

As I mentioned earlier, traumatic onycholysis yields a linear edge pattern in comparison to the jagged or digitated edge of distal subungual onychomycosis. Onycholysis is often surrounded by a pale-pink nail bed.5 Beyond traumatic onycholysis, if the practitioner suspects a psoriatic nail, he or she will notice an erythematous border at the edge of detachment or onycholysis as well as a yellow discoloration.5 

When working up nail issues as a result of an inflammatory skin issue, the practitioner may also use the dermatoscope on the hyponychium and even the proximal nail fold. With psoriatic nails, dermoscopy of the hyponychium will reveal an irregular and dilated capillary pattern.5 Dermoscopy will also show onychorrhexis and Beau’s lines clearly as well as superficial staining that may result from nail polish or socks. 

I utilize dermoscopy to confirm that a nail attached to a hammertoe or mallet toe is truly dystrophic versus onychomycotic. In these cases, the nail will be devoid of the patterns for distal subungual onychomycosis but will have significant Beau’s lines or onychorrhexis due to the chronic repetitive trauma from the pathomechanics involved. 

Dermoscopy will also allow the practitioner to differentiate a subungual hematoma from onychomycosis.5 The dark discoloration one sees in onychomycosis clinically may be fungal melanonychia or an accumulation of subungual blood. Subungual hematoma is the most common cause of brown-black discoloration in the nails and is often a result of chronic repetitive trauma from shoes or direct injury. A true subungual hematoma will show a round area with small dots or globules at the edges of the lesion.5 

Final Thoughts 

Dermoscopy of the nail unit provides a simple and efficient technique to further define a diagnosis. The reason for highlighting the distinctive features of distal subungual onychomycosis through dermoscopy is to increase diagnostic accuracy at the point of care while waiting for the mycological test results. Ultimately, dermoscopy cannot substitute for mycological testing but it can provide definite insight into nail disease, which allows for initiation of a treatment plan. 

For the patients who prefer topical therapy, dermoscopy of the nail unit may reduce diagnostic delay.6 For those who prefer oral antifungal therapy, dermoscopy can provide a diagnostic tool that can direct specimen collection for mycology and refinement of a differential diagnosis. 

Overall, dermoscopy is a useful tool that podiatrists should utilize more given the amount of nail cases most of us see on a weekly basis. After a bit of a learning curve, time and practice, the podiatric physician should be able to efficiently and accurately assess a nail with the dermatoscope, which ultimately will benefit the patient’s care.  

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

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

1. Ameen M, Lear JT, Madnan V, et al. British Association of Dermatologists’ guidelines for the management of onychomycosis. Br J Dermatol. 2014;171(5): 937-958. 

2. Piraccini BM, Balestri R, Starace M, Rech G. Nail digital dermoscopy (onychoscopy) in the diagnosis of onychomycosis. J Eur Acad Dermatol Venereol. 2013;27(4):509–513. 

3. Kaynak E, Gotkay F, Gunes P, et al. The role of dermoscopy in the diagnosis of distal lateral subungual onychomycosis. Arch Dermatol Res. 2018;310:57–69. 

4. Yorulmaz A, Yalcin B. Dermoscopy as a first step in the diagnosis of onychomycosis. Adv Dermatol Allergol. 2018;XXXV(3):251–258. 

5. Piraccini BM, Alessandrini A, Bruni F, Starace M. Dermoscopy in the diagnosis of onychomycosis. In: Rigopoulos D, Elewski B, Richert B, eds. Onychomycosis: Diagnosis and Effective Management. Hoboken, N.J.: John Wiley & Sons;2018. 

6. Bodman MA. Point-of-care diagnosis of onychomycosis by dermoscopy. J Am Podiatr Med Assoc. 2017;107(5):413-418. 

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