Don’t prescribe anything for nail infections until you do this! And 2 other important rules.
Rule #1: Don’t assume that every funny-looking toenail is caused by a fungus! The American Academy of Dermatology (AAD) and this 2017 article reported that only half of the suspected fungal nail infections are actually caused by a fungus. Other common causes of thick, discolored nails include:
- Repetitive trauma
- Psoriasis
- Onychogryphosis (Ram’s horn nail)
- Subungual malignant melanoma (don’t miss this one)
Rule #2: Don’t treat without confirmation. Given the risk of misdiagnosis and treatment failure ranging from 30-60% depending on the preferred agent, it’s highly recommended to identify the actual dermatophyte causing the infection. Diagnostic modalities for potential nail fungus include:
- Fungal culture (the expensive Gold standard that can take 2-6 weeks)
- PCR (provides quick turnaround but can detect nonpathogenic or dead fungi)
- KOH with microscopy
- PAS staining of nail clippings
Rule #3: Go systemic and give it time! The most effective treatment for onychomycosis or tinea unguinum is oral terbinafine at 250 mg per day for adults for 6-12 weeks (depending on the location of the infected nail). Though treatment is only 12 weeks at most, the medication is detectable in the nail for up to 7 and a half months following treatment. And given the slow rate of nail growth, it can be 6-12 months before the patient has a clean, clear nail.
Pearls:
- Oral terbinafine has minimal drug-drug interactions.
- While baseline liver function studies are reasonable, periodic monitoring is falling out of favor due to the low likelihood of abnormalities.
- If a proven nail fungus is hard to clear, consider combining both oral and topical therapies.
How do you approach fungal infections of the nail?
This article was medically reviewed by Phil DaVisio, DMSc, PA-C.
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