Onychomycosis (dermatophytosis of the nail) is a chronic fungal infection affecting toenails or fingernails that can involve the nail matrix, nail bed, or nail plate. Although not life-threatening, it causes significant physical discomfort and considerable psychological distress due to altered nail appearance.

Clinical Concept: Particularly in patients with comorbid conditions such as diabetes mellitus, onychomycosis can lead to serious secondary complications including cellulitis, osteomyelitis, and tissue necrosis.

1. Clinical Presentation & Subtypes

Patients typically present after months of unsuccessful home or over-the-counter remedies. Infected nails are dull, thickened, lusterless, and have a pithy consistency, with parts of the nail often breaking off.

• Distal Lateral Subungual Onychomycosis: Yellow-white appearance due to subungual hyperkeratosis and onycholysis.
• Endonyx Onychomycosis: Milky white discoloration of the nail plate without subungual hyperkeratosis.
• Total Dystrophic Onychomycosis: Characterized by a thickened, opaque, and yellow-brown nail.

Differential Diagnosis: Conditions mimicking onychomycosis include contact dermatitis, nail psoriasis, traumatic onycholysis, and lichen planus.

2. Diagnostic Workup

Because non-fungal conditions can mimic onychomycosis, diagnostic confirmation is essential:

• Microscopic KOH Exam: Microscopic examination of nail scrapings mixed with potassium hydroxide (KOH) checks for hyphae (though false-negative rates are relatively high).
• Fungal Culture & PCR: Cultures should be obtained from pulverized scrapings or clippings. Polymerase chain reaction (PCR) analysis offers advanced detection of fungal DNA.
• Dermoscopy: Useful in distinguishing fungal infection (irregular margins with yellow-white spikes projecting into the proximal nail plate) from traumatic injury.

3. Oral Antifungal Therapy & Dosing Protocols

Oral antifungals—specifically itraconazole (Sporanox®), terbinafine (Lamisil®), and fluconazole (Diflucan®)—are the most effective treatments. Older agents like griseofulvin require months of treatment and carry a high relapse rate.

Pulse Dosing Protocol: Itraconazole 400 mg daily for the first week of the month (given for 2 months for fingernails or 3 months for toenails) alternates drug use with abstinent periods. The medication accumulates in the nail matrix for months post-therapy, yielding high efficacy at lower cost and significantly reduced hepatotoxicity.