When A Patient Presents With Linear Streaks In A Nail

A 53-year-old woman presents with discoloration in both hallux toenails and has previously tried topical ciclopirox for over a year. Despite the use of the medication, there was no resolution of the nail issue.

She has concomitant tinea pedis in most interspaces. There is no pruritus. The patient notes that she doesn’t even think about the dryness there but adds that it does not go away with her regular moisturizer. She works out at a barre class daily that requires being barefoot in the studio. The patient likes to get pedicures regularly because she is concerned that her toenails are on display during the barre class. She presented for a second opinion for her nail concern.

The patient has a history of hypertension but relates no other comorbidities. The examination reveals that both halluces have a yellow spike extending from the hyponychium to a few millimeters before the cuticle. She has circular scale in between the toes on both feet but it does not extend to the plantar foot.

There are no open wounds, maceration or fluorescence with a Wood’s lamp examination. 

Key Questions To Consider

1. What are the characteristic skin lesions in this disease?
2. What is the most likely diagnosis?
3. What is your differential diagnosis?
4. What are the characteristic nail lesions in this disease?
5. What is the treatment?

Answering The Key Diagnostic Questions
1. The characteristics most associated with this nail condition are a focal linear band, multiple bands or a patch that can begin at or near the hyponychium, and extend into or stop short of the lunula. The condition is also characterized by large fungal filaments and microscopic spores that are conglomerated together into a fungal ball formation.    
2. The most likely diagnosis is a dermatophytoma.
3. The differential diagnosis includes onychomycosis.
4. The characteristic nail deformity with this condition is the linear discolored streak, streaks or a patch that can be visible in conjunction with longstanding distal subungual onychomycosis, white superficial onychomycosis and total dystrophic onychomycosis.  
5. Treatment ranges from topical antifungals to oral antifungals to surgery.

What You Should Know About Dermatophytomas
Roberts and Evans first described dermatophytoma in 1998 as a dermatophyte fungal ball that occurs in longstanding cases of onychomycosis.¹ There are few published articles on dermatophytomas so determining the frequency and the various clinical manifestations can be difficult. One can examine a sample of the debris from the dermatophytoma via KOH and culture to identify the specific dermatophyte. Judging from the literature, it appears that dermatophytomas are difficult to treat and are often recalcitrant to therapies.² There are currently no formally published papers on this entity in the podiatric literature but several case studies and letters to the editor have been published in the dermatologic literature.^2-4 That said, the concurrent onychomycosis is easily recognizable to the podiatric practitioner but the specific dermatophytoma will not be.  

The hallmark of this nail condition is a lateral streak or patch that may or may not connect with the hyponychium distally, and co-present with various types of onychomycosis.² The streak or patch may present as white, yellow, orange or brown. Authors have described it as a “fungal abscess surrounded by a biofilm.”³ A biofilm is a polysaccharide matrix that enrobes microorganisms and creates a fortress impenetrable to antimicrobials. This biofilm, encompassing dermatophyte colonies that adhere together, creates a challenge for antifungals, which ultimately make their presence an exclusion from clinical trials of new antifunguals.⁴ This creates frustration for clinicians and patients alike.  

Pertinent Treatment Insights
It is important to recognize this subtype of onychomycosis due to its difficulty in responding to treatment. Baran and coworkers recommended surgical avulsion in addition to topical therapies.² Martinez-Herrera and coworkers agreed, discussing the use of urea to dissolve the nail with subsequent application of a topical antifungal.^2,5 There is no evidence-based medicine to support the best treatment for a dermatophytoma but a combination of debridement, whether mechanical, surgical or chemical (urea), along with an antifungal therapy seems to be the best practice at this time. If the patient allows, I would prefer to debride the hyperkeratotic, onycholytic streak as much as possible (as opposed to surgical removal of the nail) and follow with either a topical or oral antifungal.  

The first topical antifungal formally reported in the literature to eradicate a dermatophytoma is efinaconazole 10% solution (Jublia, Valeant Pharmaceuticals).⁴ However, when reviewing the literature for topical onychomycosis therapies, dermatophytomas have inadvertently made their way into clinical trials for poly-ureaurethane 16% solution (Nuvail, Cipher Pharmaceuticals) and tavaborole 5% solution (Kerydin, PharmaDerm). Nuvail has an FDA-approved indication for nail dystrophy but Nasir and colleagues described the use of the product for onychomycosis, and Kerydin is indicated for mild to moderate onychomycosis of the toenail.^6,7 Although the published reports on the clinical trials of these products did not formally present or discuss patients with dermatophytomas, these patients did have a positive change in their appearance. This is evident in Nuvail’s six-month follow-up data post-treatment and in the original poster presented by Elewski and co-workers for Kerydin.^6,7

Keys To The Differential Diagnosis Of Dermatophytomas
Onychomycosis or tinea unguium is the result of invasion of the nail unit by dermatophytes, non-dermatophyte molds and/or Candida albicans. Clinicians may see concomitant tinea pedis or tinea cruris in patients with onychomycosis. As a practitioner, it is important for you to recognize a dermatophytoma in the presence of an onychomycosis presentation.  

The most common form of onychomycosis in the lower extremity is distal lateral subungual onychomycosis caused by Trichophyton rubrum. Clinically, it may be difficult to distinguish onychomycosis from other existing nail pathologies. KOH preparation, periodic acid Schiff (PAS) staining and fungal culture can aid in determining the presence of a dermatophyte-caused infection.

The best evidence for treatment for onychomycosis includes the topical antifungals (tavaborole, efinaconazole, ciclopirox) and oral antifungals (terbinafine, itraconazole, griseofulvin). The FDA statement regarding devices like the laser for treatment of onychomycosis do not imply efficacy by saying “temporary improvement in the appearance of the nail.” Consider lasers as ancillary therapy to a topical or oral antifungal instead of monotherapy for a dermatophytoma as the use of lasers for this clinical entity has not yet been established.  

Final Notes  
For this patient, I chose nail debridement of the streak as aggressively as the patient would allow. I sent the subungual debris for KOH and fungal culture to confirm the diagnosis of onychomycosis. Lab studies confirmed the dermatophytoma’s clinical appearance. After this confirmation and normal liver function testing results, I placed the patient on oral terbinafine 250 mg once daily for three months to cover both the nail disease and the concomitant tinea pedis. In addition to the oral antifungal, I also prescribed a topical antifungal solution once daily at bedtime until the streak grew out. The patient will have periodic monitoring for nail changes.

Dr. Vlahovic is an Associate Professor and J. Stanley and Pearl Landau Fellow at the Temple University School of Podiatric Medicine. She writes a monthly blog for Podiatry Today. Readers can access Dr. Vlahovic’s blog at https://tinyurl.com/qbe6s4w .

References

1. Roberts DT, Evans EGV. Subungual dermatophytoma complicating dermatophyte onychomycosis. Br J Dermatol. 1998;138:189-90.
2. Martinez-Herrera E, Moreno-Coutiño G, Fernández-Martínez RF, et al. Dermatophytoma: description of 7 cases. J Am Acad Dermatol. 2012;66(6):1014-6
3. Burkhart, CN, Burkhart, CG, Gupta, AK. Dermatophytoma: Recalcitrance to treatment because of existence of fungal biofilm. J Am Acad Dermatol. 2002; 47(4):629–631.
4. Cantrell W, Canavan T, Elewski B. Report of a case of a dermatophytoma successfully treated with topical efinaconazole 10% solution. J Drugs Dermatol. 2015;14(5):524-6.
5. Baran R, Hay R, Haneke E, Tosti A. Mycological Examination: Onychomycosis: The Current Approach to Diagnosis and Therapy, Second Edition. Taylor and Francis Group, Boca Raton, FL, 2006, pp. 49-70.
6. Nasir A, Goldstein B, van Cleeff M, Swick L. Clinical evaluation of safety and efficacy of a new topical treatment for onychomycosis. J Drugs Dermatol. 2011;10(10)1186-1191.
7. Elewski BE, et al. Effectiveness and safety of tavaborole, a novel boron-based molecule for the treatment of onychomycosis: results from two phase 3 studies. Presented at Desert Foot 2013, November 20-22, 2013, Phoenix, AZ.

For further reading, see “Keys To Managing Severe Onychomycosis” in the May 2013 issue of Podiatry Today or “Roundtable Insights On Treating Onychomycosis” in the May 2011 issue.

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