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) 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
  • 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:

How do you approach fungal infections of the nail? 

See what’s next in our Clinical Medicine series:

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