From ATLANTA Medicine, Vol. 85, No. 5
With an estimated 35 million cases each year, Onychomycosis (fungal infection of the nail unit) is one of the most common dermatological problems in the United States. While oral medications carry risks and often do not produce a lasting cure, new topical medications provide viable monotherapy alternatives.
Medical and consumer organizations are focusing on quality and safety in the diagnosis and treatment of nail fungus. The American Academy of Dermatology has collaborated with Choosing Wisely, a trademarked national initiative of the American Board of Internal Medicine (ABIM), to promote the most appropriate, cost-effective, evidence-based treatment. One of their five recommendations is to confirm nail fungus prior to starting oral therapy. This article will present information that may assist clinicians in diagnosing and treating this condition.
Types of Nail Fungus
It is estimated that only half of the cases diagnosed as fungal nails, and in some cases treated as fungal nails, are fungal. The other 50 percent of dystrophic nails are conditions that mimic fungal nails. Of the 50 percent that are fungal, 90 percent are dermatophyte. Ten percent are mold or other opportunistic organism. (Bologna)
There are several types of nail fungus:
1. Distal/lateral nail – commonly T. rubrum
2. Superficial white – often T. metagrophytes, cephalosporium, Aspergillus, Fusarium and, in HIV patients, T. rubrum.
3. Proximal subungual – less common and often with immunosuppression.
4. Destructive nail plate_– with marked hyperkeratosis and often with paronychial involvement. This is seen in immunosuppressed cases or chronic mucocutaneous candidiasis. (Andrews)
Testing and Diagnosis
Dystrophic nails may appear as fungus, but a culture is needed to confirm fungus. No single method to confirm nail fungus provides 100 percent sensitivity. When a culture is taken, the dystrophic nail and subungual debris at the junction of the attached nail and nail bed must be submitted.
To obtain a nail culture, clip away loose nail plate and take the culture from the junction where the nail plate attaches to the nail bed. Having the proper tools to obtain this specimen is key. Many labs will accept nail clippings, so maintaining various media in the office is not necessary.
The nail plate may also be sent for PAS stain. This has a higher degree of accuracy (41-93 percent) than culture. Taking this sample requires a full thickness nail plate clipping. This does not require a biopsy of the nail bed, an invasive procedure. The sample is submitted to a pathology lab.
KOH shaving, which requires a very thin sample of the distal nail, is reported at 57 percent sensitive. The KOH result is impacted by collection technique and experience/training of the microscopic examiner.
The KOH and the PAS tissue stain confirm hyphal elements but cannot provide species identification. A fungal culture may provide species identification, but this may not add value to treatment. Additionally, KOH is an office procedure, while the PAS stain is a lab test. (Weinberg JM et al. J Am Acad dermatog 2003,49193-197)
If the fungal culture returns negative, be sure the patient has not used topical antifungal preparation prior to the culture. Taking a second culture for fungus of the nails is helpful. If the second culture is negative, the problem may not be nail fungus.
The differential diagnosis of nail fungus includes psoriasis, lichen planus, squamous cell carcinoma, verruca, and other eczematous dermatosis. Squamous cell carcinoma is the most challenging and is a rare occurrence in dystrophic nails. It is more common in the fingernail than toenail, but does occur in both.
Periungual erythema and pain may be clues to squamous cell carcinoma. Onycholemmal carcinoma is a distinct type of squamous cell carcinoma arising from the nail isthmus. It is an indolent carcinoma confirmed by biopsy. (Chaser, BE, Renszel, KM, Crowson et al Oncholemmal carcinoma: A morphologic comparison of 6 reported cases. JAAD.2012.07.015)
If the nail culture is negative on two samples, consider a podiatry or dermatology consultation. If the nail is painful, bleeding or shows erythema, it may be important to send the patient for a nail bed biopsy.
Treatment of nail fungus is challenging. The toenail grows slowly, only 1mm per month, fully regrowing in 12 to 18 months. The fingernail may regrow in six months.
Oral medications are not always effective, have systemic risk and may interact with other medications. When informed of the risks, many patients decline treatment. Lab testing prior to, and during, treatment is recommended, based on the oral medication selected.
Pulse oral treatment may provide higher cure rates and reduced systemic risk. Treatment with oral medication has a high relapse rate. Clinical cure, where the nail appears normal, may not be confirmed by a mycological cure.
There are other considerations in treating fungal nails. The infected nails may infect others in the home. Studies have shown that the specific genetic type of T. rubrun infection is the same from adults with fungal infection in the same household.
There are new topical medications for fungus of the nail.
Efinaconazole 10 percent is the first topical triazole antifungal agent approved by the FDA. Tavaborole 5 percent is a boron-based benzoxaborole that has completed phase 3 trials.
Laser treatment with Nd:Yag is currently approved in the U.S. for temporary increase in clearing of nail fungus. The reports from randomized controlled trials do not show significant mycological or clinical clearance. (Hollmig, T et al JAAD 2013. 12.024 p911 923)
1. Dermatology Essentials, Bolognia, Schaffer, Duncan, Ko Elservier Saunders C 1914
2. Dermatology Third Edition Bolognia, Jorizo, Schaffer, Elservier Suanders c 2012 reprinted 2013
3. Dermatoloical Signs of Internal Disease Fourth Edition Callen, Jorizzo, Bolognia, Piett3 ZoneSaunders, Elsevier c2003
4. Andrews Diseses of the skin Eleventh Editiion James, Berger, Elston Elsevier Saunders c 2011
5. Clinical Dermatology Fifth Edition Habif Mosby Elsevier c 2010
Choosing Wisely is a registered trademark of the ABIM Foundation