– The way Neal Bhatia, MD, sees it, there is no such thing as a classical presentation of onychomycosis.

Dr. Neal Bhatia, director of clinical dermatology research at  Therapeutics Clinical Research, San Diego. Doug Brunk/MDedge News

Dr. Neal Bhatia

“This is where proving your diagnosis is half the battle, even though we are sometimes using empiric therapy in suspected cases,” he said at Skin Disease Education Foundation’s annual Las Vegas Dermatology Seminar. “Prove the diagnosis and get the extra tests necessary.”

According to Dr. Bhatia, director of clinical dermatology research at San Diego-based Therapeutics Clinical Research, tinea unguium, tinea corporis, tinea cruris, and tinea pedis account for more than half of all visits for dermatophytosis. With onychomycosis, the ultimate treatment goal from the standpoint of clinicians is no more fungus, he noted, while the desired endpoint from the standpoint of some patients is normal-looking nails.

“Endpoint failures in a research trial are not the same as what we tell patients in the clinic,” Dr. Bhatia said. “If you have a patient using something topical for 52 weeks and they see two-thirds of their nail improve, you’re not going to say, ‘Stop; you’re a failure now.’ You tell them, ‘Keep going and we’ll keep watching.’ But in the research world, it’s very different when you look at all of the different endpoints that have to be met at the finish line. It’s very important to measure success based on what that patient’s experiencing.”

According to Dr. Bhatia, diagnosing onychomycosis by visual assessment has a sensitivity of 77% and a specificity of 47%, while KOH has a sensitivity between 67% and 93% and specificity between 38% and 78%. PCR, meanwhile, “is quick, but it’s expensive and it has a high false-positive rate. So, in those difficult patients who aren’t responding [to treatment], maybe we can’t just trust our eyes alone [to make a diagnosis].”

Tests such as a KOH stain have low sensitivity, with high costs of more sensitive tests such as the periodic acid–Schiff (PAS) stain. In a recent study, researchers conducted a retrospective cohort analysis of 600 patients with toenail clippings sent for PAS stain during January 2000–December 2013 (J Am Acad Dermatol. 2015 May; 72(5):AB116). They reviewed records to determine which PAS stains were performed to confirm probable clinical diagnosis of onychomycosis.

The researchers found that 30% of toenail clippings were sent for confirmatory PAS staining by dermatologists, compared with 37% by podiatrists and 34% by other clinicians. Of these tests, 75% ordered by dermatologists were positive for fungus, compared with 81% ordered by podiatrists, and 66% ordered by other physicians. “The positive predictive value of clinical suspicion for true onychomycosis was high, and the findings question whether or not a confirmatory test is really necessary,” Dr. Bhatia said.

Preventative strategies to control recurrence of onychomycosis include using maintenance regimens of the recommended antifungal agent, discarding old shoes, alternating wearing different pairs of shoes, periodically disinfecting shoes, washing feet regularly, and alerting the physician to the first sign of infection.

In an effort to investigate strategies to minimize recurrence of onychomycosis, Dr. Bhatia and colleagues evaluated 73 patients over the course of 7 years who were taking either terbinafine or itraconazole (J Drugs Dermatol. 2016;15[3]:279-82). Thirty-six months later, the overall mean recurrence rate among patients was 14%. Prognostic factors influencing recurrence included patient’s family history; lifestyle; underlying physiology (presence of a very thick nail, extensive involvement of the entire nail unit, lateral nail disease and yellow spikes); physical trauma, especially in the elderly; concomitant disease, such as peripheral artery disease and/or diabetes; immunocompromised or immunosuppressed patients, and the presence of tinea pedis.

Based on their analysis, they recommended the following strategies to prevent or limit recurrence: prophylactic use of a topical antifungal twice-weekly for 2-3 years; periodic application of a topical antifungal to plantar surface and/or interdigital spaces; treatment of any coexisting tinea pedis; treating immediate family members; footwear and sock decontamination with antifungal powder; ultraviolet light or ozone; avoidance of activities known to risk spread of disease, such as communal swimming pools.

Dr. Bhatia concluded his presentation by noting that the ideal treatment for onychomycosis would not pose a systemic risk to the liver, heart, or other organs; would not require monitoring of labs; would not require debridement; and would not interact with other drugs. It would also penetrate the nail plate – especially the diseased nail – and would be quick drying.

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Dr. Bhatia disclosed having affiliations with Actavis, Allergan, Anacor, Aqua, Bayer, Biofrontera, BiopharmX, Cipher, Dermira, Dusa, Exeltis, Ferndale, Foamix, Galderma, Intraderm, ISDIN, LaRoche-Posay, Leo, Novan, Novartis, PharmaDerm, Promius, Regeneron, Sanofi, Sun Pharma, and Valeant.