Onychomycosis

Onychomycosis is a fungal infection of the nail unit, most commonly affecting toenails. It is caused predominantly by dermatophytes such as Trichophyton rubrum and Trichophyton mentagrophytes, but yeasts (notably Candida species) and nondermatophyte molds can also produce nail infection. The fungus invades the nail plate and nail bed, leading to gradual nail dystrophy.

Clinically, nails become thickened, discolored (yellow or brown), and brittle. Subungual hyperkeratosis and onycholysis (separation of nail from the nail bed) are common. Pain or discomfort can occur with shoe pressure; functional impairment is more likely with multiple nails involved.

Diagnosis relies on clinical assessment supported by laboratory tests. Direct microscopy of nail clippings or debris with potassium hydroxide reveals fungal elements; fungal culture can identify the organism; histopathology with periodic acid–Schiff stain is an option; newer molecular methods (PCR) are available in some centers. Distinguishing from trauma, psoriasis, or other nail conditions is important.

Treatment depends on severity, number of nails involved, and patient factors. Topical antifungals (ciclopirox, efinaconazole, tavaborole) may be suitable for mild disease or when only a few nails are affected. Systemic therapy with terbinafine is the preferred option for most cases of distal and proximal subungual onychomycosis or extensive disease, with itraconazole or fluconazole as alternatives. Therapy lasts weeks to months; nails take many months to regrow. Systemic agents require liver function monitoring and attention to drug interactions and contraindications, including pregnancy.

Prevention and management include good foot hygiene, keeping nails short and dry, avoiding trauma, treating tinea pedis, using separate nail tools, and wearing breathable footwear. Recurrence is common after treatment.