Rule #1: Don’t assume that every funny-looking toenail is caused by a fungus! The American Academy of Dermatology (AAD) reports that less than half of suspected fungal nail infections are actually caused by a fungus. Other common causes of thick, discolored nails include:
- Repetitive trauma
- 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.
- 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.
How do you approach fungal infections of the nail?
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