MNT Onychomycosis and Fungal Infections 1 — Questions and Answers
Question 1: The most common causative organism of onychomycosis is:
- Candida albicans
- Trichophyton rubrum (Correct answer)
- Aspergillus niger
- Epidermophyton floccosum
Correct answer: Trichophyton rubrum
Trichophyton rubrum is the most prevalent dermatophyte causing onychomycosis worldwide, accounting for approximately 70% of cases.
Question 2: Distal-lateral subungual onychomycosis (DLSO) characteristically begins at the:
- Proximal nail fold
- Distal and lateral nail bed, progressing proximally (Correct answer)
- Nail matrix
- Ventral nail plate surface
Correct answer: Distal and lateral nail bed, progressing proximally
DLSO is the most common clinical pattern, starting at the hyponychium (distal nail bed) and spreading proximally beneath the nail plate.
Question 3: Which clinical sign distinguishes proximal subungual onychomycosis (PSO) from other types?
- Yellow discoloration starting at the free edge
- White opacity beginning at the proximal nail plate near the cuticle (Correct answer)
- Total nail plate destruction
- Green discoloration throughout
Correct answer: White opacity beginning at the proximal nail plate near the cuticle
PSO presents with white/opaque discoloration at the proximal nail, near the cuticle, as fungi enter through the proximal nail fold; it is often associated with immunosuppression.
Question 4: Nail debridement in onychomycosis management primarily aims to:
- Cure the fungal infection permanently
- Reduce fungal load and improve topical antifungal penetration to the nail bed (Correct answer)
- Prevent regrowth of the nail plate
- Eliminate all keratin debris permanently
Correct answer: Reduce fungal load and improve topical antifungal penetration to the nail bed
Mechanical debridement removes infected nail material, reducing fungal burden and allowing topical agents to penetrate more deeply to the infection site.
Question 5: KOH (potassium hydroxide) preparation is used in onychomycosis diagnosis to:
- Identify bacterial coinfection
- Dissolve keratin and visualize fungal hyphae microscopically (Correct answer)
- Culture the specific species
- Stain the nail for photographic documentation
Correct answer: Dissolve keratin and visualize fungal hyphae microscopically
KOH dissolves keratin without destroying fungal cell walls, allowing microscopic visualization of hyphae, pseudohyphae, or spores to confirm fungal infection.
Question 6: White superficial onychomycosis (WSO) is characterized by:
- Deep nail bed invasion
- Chalky-white patches on the dorsal nail plate surface that scrape off easily (Correct answer)
- Proximal white leukonychia
- Subungual hyperkeratosis only
Correct answer: Chalky-white patches on the dorsal nail plate surface that scrape off easily
WSO affects only the surface of the nail plate, presenting as white, powdery or chalky patches that can be scraped off; it is most commonly caused by T. mentagrophytes.
MNT Onychomycosis and Fungal Infections 1
The most common causative organism of onychomycosis is: