Expert Shares Her Tips for Diagnosing, Treating Onychomycosis

NEW ORLEANS — Don't treat suspected cases of onychomycosis before confirming the diagnosis with a laboratory test, Boni E. Elewski, MD, advises.

"The PAS [periodic acid-Schiff] stain is very popular because it can identify the presence or absence of fungal elements, but a fungal culture will identify the organism living in the nail," Elewski, professor and chair of dermatology at the University of Alabama, Birmingham, said at the annual meeting of the American Academy of Dermatology. "You also could do a PCR to identify the organism, with or without a KOH or PAS stain. It is often helpful to know what organism is causing the infection."

Dr Boni E. Elewski

While waiting for lab results, there are three clinical clues to look for — the first being that an infection likely resides in the toenail. "You almost never see dermatophyte onychomycosis in the fingernails without it being in the toenails, too," Elewski said.

The presence of tinea pedis is a second clinical clue. "Sometimes it's subtle, so I will ask the patient, 'Have you been treating yourself for athlete's foot?' If they say 'no, I've never had it,' put down on your list that it's unlikely they have onychomycosis. How is the fungus going to jump from the floor into the nail without taking a little vacation on the bottom of the foot? It just isn't going to happen."

The presence of dermatophytoma is the third clinical clue. "These are dermatophyte abscesses encased in a biofilm, and they're really hard to treat," she said.

Treatments

Clinicians typically turn to one of three oral drugs for treating onychomycosis: terbinafine, itraconazole, and fluconazole, Elewski noted. Referring to terbinafine as "the gold standard," she said that she typically writes a prescription for 90 250-mg pills. "When I give terbinafine, I often do baseline liver profiling, depending on the patient's age, their state of health, their comorbidities, and other medications they're taking," she said. "If they're 18 years old and otherwise healthy, I probably don't." While she generally prescribes 90 pills, she added, "keep in mind that 90 pills are not going to cure everybody. I see the patient 4 months later because the drug should stay in the nail for 30 days or more at therapeutic levels after you take that 90-day course."

Another option is itraconazole, which can be taken at a dose of 200 mg a day for 12 weeks, or at a pulse dose, where patients take 400 mg every day for 1 week, 1 week a month, for 4 consecutive months. "I'll often do a baseline liver profile with itraconazole, too," Elewski said. "I don't think you have to, but it makes sense if it's feasible for you. Decide that based on each patient."

Itraconazole can't be given concomitantly with statins because of the potential for rhabdomyolysis. For patients taking statins, she consults with their physicians to make sure it's safe to stop the statin a couple of days before and after their scheduled pulse dose of itraconazole. "This involves 1 week per month of taking itraconazole without the statin," she said. "Or they could stop statins for the time you treat, if cleared by their doctor."

As for fluconazole, Elewski usually prescribes 200 mg once or twice per week until the nail is normal. She offers patients the mnemonic for "Fungal Fridays" or "Toesdays" as a way for them to remember which day to take the fluconazole.

According to data in the package inserts, rates of complete and mycologic cures are 38% and 70% for terbinafine, respectively, 14% and 54% for itraconazole, and 37% to 48% and 47% to 62% for fluconazole. "These cures are not 100% based on the standard course [of the drug]," Elewski noted. "I don't use the standard course. I believe in treating to terminate. You want to kill the fungus."

Resistant Dermatophytes 'Are Coming'

Halting treatment with an oral drug at a particular time point instead of when the nail is fungal-free likely contributes to resistant strains, she added, noting that she has at least two dozen patients in her practice with dermatophyte resistance documented in labs. "We need to be antifungal stewards, because resistant dermatophytes are coming to us," she said. "They're here already, and we don't want it to be endemic in the US."

In a published study from 2020, researchers from India enrolled 200 patients with relapsing tinea corporis, tinea cruris, and tinea faciei and allocated 50 each to treatment with either fluconazole, griseofulvin, itraconazole, or terbinafine. At week 4, all treatment arms had cure rates of less than 8%. At week 8, the cure rates were 42% for fluconazole, 16% for griseofulvin, 28% for terbinafine, and 66% for itraconazole.

Based in part on these study findings, Elewski said that she has become more aggressive in her therapeutic approach, including treating some of her patients on terbinafine for a minimum of 6 months. "If that's not enough, I keep treating," she said. "But, patients may not respond to terbinafine; we see resistance. So, itraconazole may be our best drug going forward for treating onychomycosis. You just have to watch out for side effects of itraconazole, mainly drug-drug interactions."

Elewski reported having no relevant financial disclosures related to her presentation.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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Cite this: Doug Brunk. Expert Shares Her Tips for Diagnosing, Treating Onychomycosis - Medscape - Mar 23, 2023.