Author:

• Sarah Kinsey

Faculty Reviewer:

• Aaron Secrest

Publish date: Posted on March 8, 2021May 17, 2022
Last updated: May 17, 2022

Keywords #

dermatophyte
fungal culture
fungal nail infection
nondermatophyte
onychomycosis
tinea pedis
Trichophyton rubrum
yeast

Diagnosis #

Onychomycosis is a fungal infection of the nail caused by dermatophytes, nondermatophytes and yeast. Onychomycos is commonly presents with nail dystrophy or an abnormal appearing nail and can cause patients embarrassment, pain, difficulty performing activities of daily living and can be a source for secondary bacterial infections. Confirmatory mycologic testing should be done prior to initiating treatment.[1] Though onychomycosis rarely self-resolves, treatment is not always necessary and depends on the degree of nail involvement, causative organism, comorbidities(diabetes), other medications, and patient preferences.[2]

Key Concepts #

• Onychomycosis is a chronic fungal infection of the nail.
• The most common cause of onychomycosis is Trichophyton rubrum, adermatophyte.[1]
• It is seen more frequently on toenails (especially the great toe) than fingernails.
• Onychomycosis accounts for only about half of all abnormal-appearing nails, making confirmatory testing an important part of diagnosis prior to treatment.
• The mainstays of onychomycosis treatment are oral and topical antifungals.

Epidemiology #

The worldwide prevalence of onychomycosis is 5.5%.[1] It is more common in adults than children; prevalence increases with age. In a multicenter study of 15,000 Canadian patients, onychomycosis confirmed by mycologic examination accounted for approximately 47.8% of abnormal appearing nails.[3] Patients with diabetes, psoriasis, immunosuppression (from HIV or kidney transplant) and patients on dialysis are at increased risk of contracting onychomycosis.[4] Nail trauma, concomitant tinea pedis and onychomycosis in other household members represent additional risk factors.[5,6,7]

Clinical Features #

• The hallmark of onychomycosis is nail dystrophy or an abnormal appearing nail that worsens slowly overtime, often without an inciting event (though trauma is a risk factor).
• Yellowing or discoloration of the nail.
• Subungual hyperkeratosis (scaling underneath the nail) .
• Onycholysis (separation of the nail from the nail bed).
• Nail thickening, nail splitting and nail brittleness.
• Onychomycosis is more common in toenails (especially the great toenail).
• Dermoscopy can demonstrate a fringed proximal border or longitudinal striae in the area of onycholysis.[1]
• Onychomycosis subtypes vary by the pattern of nail invasion. Distal and lateral subungual onychomycosis (DLSO) is most common. Proximal subungual onychomycosis (PSO) is much less common and should raise concern for immunosuppression.[1,8]

Differential Diagnoses #

• Psoriasis
• Lichen planus
• Verruca vulgaris
• Squamous cell carcinoma
• Cutaneous squamous cell carcinoma
• Idiopathic or traumatic onycholysis
• Subungual exostosis
• Paronychia
• Onychomatricoma
• Yellow nail syndrome
• Subungual melanoma

Diagnostic Workup #

As only half of nail dystrophy appears due to onychomycosis, when onychomycosis is suspected based on history, exam findings and/or dermoscopy, confirmatory testing is beneficial prior to initiating treatment. Appropriate diagnostic tests are as follows:

• Potassium hydroxide and microscopy –rapid and cost effective but requires expertise
• Histopathology –rapid, most sensitive technique, good for ruling out nail psoriasis, need access to pathology services, expensive, more difficult to evaluate PSO.
• PCR –rapid (1-2 days), sensitive, identifies organism, more expensive, may not be covered by insurance, may detect nonviable fungi
• Fungal culture –identifies causative organism, slow(3-4 weeks), low sensitivity

Treatment #

If any one of the rapid diagnostic tests is positive, initiate empiric treatment for dermatophyte infection while awaiting fungal culture results. Patient characteristics including nail findings, pathogenic organisms and comorbidities will determine response to treatment. Onychomycosis severity index can be used to predict response to antifungal therapy. Oral and topical antifungals are the mainstays of onychomycosis treatment. The decision to use oral vs topical medications will depend on a variety of factors including clinical judgement. Indications for oral antifungals include PSO, more severe DLSO, greater than 3-4 nails effected, poor prognostic factors and factors limiting patient compliance with topical therapy. Terbinafine is the first-line oral medication, followed by itraconazole. Indications for topical therapy include mild/moderate DLSO disease burden as defined by affecting <50% of nail plate, nail plate <2mm thick, and sparing the nail matrix, up to 3-4 nails affected, patients at risk of adverse response to systemic therapy, and pediatric patients. Topicals include:

• Ciclopirox (8% nail lacquer) –inhibits cytochromes, complete cure rate 5.5-8.5%, pregnancy category B, also approved for fingernails
• Efinaconazole (10% solution) –inhibits lanosterol 14a-demethylase, complete cure rate 15.2-17.8%, pregnancy category C, not forfingernails
• Tavaborole (5% solution) –inhibits fungal tRNA synthetase, complete cure rate 6.5-9.1%, pregnancy category C

All topicals listed have broad spectrum efficacy against dermatophytes, nondermatophytes and candida and should be applied daily to toenails for 48 weeks. Additional strategies to improve treatment efficacy and prevent recurrence include concomitant treatment of tinea pedis, avoidance of occlusive footwear, wearing flip-flops in public gyms and swimming pools, discarding or treating infected socks and footwear, and avoidance of nail trauma by keeping nails short.[2]

References #

1. Lipner, Shari R., and Richard K. Scher. “Onychomycosis: clinical overview and diagnosis.”Journal of the American Academy of Dermatology80.4 (2019): 835-851.
2. Lipner, Shari R., and Richard K. Scher. “Onychomycosis: Treatment and prevention of recurrence.”Journal of the American Academy of Dermatology80.4 (2019): 853-867.
3. Gupta, Aditya K., et al. “Prevalence and epidemiology of onychomycosis inpatients visiting physicians’ offices: a multicenter Canadian survey of 15,000 patients.”Journal of the American Academy of Dermatology43.2 (2000): 244-248.
4. Gupta, A. K., D. Daigle, and K. A. Foley. “The prevalence of culture‐confirmed toenail onychomycosis in at‐risk patient populations.”Journal of the European Academy of Dermatology and Venereology29.6 (2015): 1039-1044.
5. Avner, S., N. Nir, and T. Henri. “Fifth toenail clinical response to systemic antifungal therapy is not a marker of successful therapy for other toenails withonychomycosis.”Journal of the European Academy of Dermatology and Venereology20.10 (2006): 1194-1196.
6. Molecular Analysis of Dermatophytes Suggests Spread of Infection Among Household Members
7. Ghannoum, Mahmoud A., et al. “Molecular Analysis of Dermatophytes Suggests Spread of Infection Among Household Members.” Cutis, vol. 91, no. 5, 2013, pp. 237–245.
8. Hay, Roderick J., and Robert Baran. “Onychomycosis: a proposed revision of the clinical classification.” (2011): 1219-1227.