Onychomycosis

See Nail Disorders — Approach for the broader nail-complaint differential.

Condition

Affects 3–5% of the population, and 40% of people over 60. Toenails are affected more commonly than fingernails. Classified as superficial, distal, or proximal:

• Distal subungual onychomycosis — the first stage: hyperkeratosis of the internal surface of the distal nail plate and distal nail bed (hyponychium). Caused by Trichophyton mentagrophytes var. interdigitale (typical of toe web-space tinea, responds well to terbinafine) or Trichophyton rubrum (common on the sole of the foot, more resistant).
• White superficial onychomycosis — also common, usually confined to the toenails, with small superficial white plaques with distinct edges; caused by T. mentagrophytes var. interdigitale.
• Total dystrophic onychomycosis — progressive nail involvement: whole nail affected, thickened, opaque, and yellow-brown; caused by Trichophyton sp.

Diagnosis

Always confirm by culture and histology — use clippings (distal nail plate) for thickened, crumbling nails, or scrapings from under/on the nail surface.

Treatment

Many topical nail preparations are available OTC but have limited efficacy and lack evidence for their use. Onychomycosis needs oral antifungal treatment:

• Terbinafine 250mg daily for 12 weeks (toenails) or 6 weeks (fingernails).
• Or itraconazole 200mg twice daily for 1 week each month, for 3–4 months (toenails) or 2 months (fingernails).
• Or fluconazole 150–300mg once weekly for 24–52 weeks (toenails) or 12–24 weeks (fingernails).

Terbinafine has a cure rate of 70–80% — more effective than itraconazole or fluconazole.

Most nails with extensive onychomycosis still look abnormal after 3 months’ treatment, as a new nail takes up to 9 months to grow. When disease is extensive:

• If healthy, clear nail starts appearing at the proximal nail fold after one course of treatment, give a second course.
• If no clear nail appears at the proximal nail fold after one course, refer to an expert.

Assessing response: make a scratch with a scalpel blade at the proximal end of the dystrophy after the first course; the patient can follow the scratch as the nail grows out. If the dystrophy stays distal to the scratch, no more treatment is needed; if it moves proximal to the scratch, refer to an expert.