Onychomycosis

Onychomycosis - Fungal Nail Invaders

• Definition: Fungal infection of the nail unit (nail plate, bed, matrix).
• Epidemiology: Common, prevalence ↑ with age; significant in India.
• Risk Factors:
  • Diabetes mellitus
  • Peripheral Vascular Disease (PVD)
  • Immunosuppression
  • Chronic tinea pedis
  • Occlusive footwear
• Etiology:
  • Dermatophytes (Most common):
    • Trichophyton rubrum
    • Trichophyton mentagrophytes
  • Yeasts:
    • Candida albicans (esp. fingernails, associated with chronic paronychia)
  • Non-Dermatophyte Molds (NDMs):
    • Aspergillus spp., Fusarium spp., Scopulariopsis brevicaulis
    • Often soil saprophytes, opportunistic pathogens.

⭐ Trichophyton rubrum is the most common etiological agent for onychomycosis globally and in India.

Onychomycosis - Nail's Many Woes

Clinical classification is based on the pattern of nail invasion.

⭐ Proximal Subungual Onychomycosis (PSO) is strongly associated with HIV infection and indicates underlying immunosuppression.

Onychomycosis - Spotting the Spores

Diagnosis confirmation is crucial before systemic therapy.

• Specimen Collection:
  • Nail clippings (distal, crumbling) & subungual debris.
  • Avoid topical antifungals for 1-2 weeks prior.
• Diagnostic Tests:
  • Direct Microscopy (KOH Mount): Rapid, inexpensive. Uses $10-40%$ KOH solution $\pm$ DMSO. Visualizes hyphae, arthrospores. Sensitivity $\approx extbf{60-80}%$.
  • Fungal Culture: Gold standard for species ID. Sabouraud Dextrose Agar (SDA) $\pm$ cycloheximide. Slow growth (2-6 weeks). Sensitivity $\approx extbf{40-60}%$.
  • Histopathology (Nail Biopsy with PAS stain): Periodic Acid-Schiff stain highlights fungal elements. Highest sensitivity ($ extbf{80-95}%$). Useful if KOH/culture negative but high suspicion.
  • Dermoscopy: Shows patterns (e.g., longitudinal striae, spiked pattern, ruin-like appearance).
  • Newer Methods: PCR (high sensitivity, rapid), Dermatophyte Test Medium (DTM - color change).

⭐ PAS staining of a nail clipping is the most sensitive diagnostic test for onychomycosis.

Onychomycosis - Kicking the Fungus

• Goals: Achieve mycological and clinical cure, and prevent recurrence. Treatment choice depends on clinical type, severity, specific organism, and patient factors.
• Topical: For mild-moderate cases (e.g., WSO, <50% nail involvement, no lunula). Examples: Ciclopirox 8% lacquer, Amorolfine 5% lacquer. Duration: 6-12 months.
• Systemic: For moderate-severe cases (DLSO with lunula involvement, PSO, or multiple nail involvement).
  • 📌 'Terbinafine for Toes, Itraconazole in Pulses' | Drug | Dose | Duration (FN/TN) | Key S/E / Monitor | |--------------|------------------------------------------|----------------------------------|-------------------| | Terbinafine | 250 mg/day | 6w / 12w | Monitor LFTs | | Itraconazole | 200 mg/day OR 200mg BID 1wk/mo | 6w/12w or 2/3-4 pulses | Monitor LFTs | | Fluconazole | 150-300 mg weekly | 6-12 months | GI upset |
• Combination: Systemic + topical may ↑ cure.
• Adjuncts: Nail debridement/avulsion, laser therapy.
• NDM/Candida: Itraconazole often preferred. Resistance common.
• Prevention: Treat tinea pedis, hygiene, avoid trauma.

⭐ Terbinafine 250 mg/day for 12 weeks is first-line for dermatophyte toenail onychomycosis (high efficacy, fungicidal).

High-Yield Points - ⚡ Biggest Takeaways

• Most common cause: Trichophyton rubrum.
• DLSO (Distal Lateral Subungual Onychomycosis) is the most frequent clinical type.
• Diagnosis: KOH mount (septate hyphae) and fungal culture are key; PAS stain for nail biopsy.
• Oral terbinafine is first-line for dermatophyte onychomycosis; requires LFT monitoring.
• Topical therapy (e.g., ciclopirox, efinaconazole) for superficial white onychomycosis or mild DLSO.
• PSO (Proximal Subungual Onychomycosis) is often linked to immunosuppression (e.g., HIV).