A 6-year-old child has scaly alopecic patches on the scalp. Hair plucks show arthrospores filling the hair shaft on KOH mount. Which is the most likely causative agent?
- A Microsporum canis
- B Microsporum audouinii
- C Trichophyton tonsurans ✓
- D Epidermophyton floccosum
Correct answer: C. Trichophyton tonsurans
Explanation
Spores within the hair shaft define an endothrix pattern, classically caused by Trichophyton tonsurans (and Trichophyton violaceum). Microsporum canis and Microsporum audouinii produce an ectothrix pattern with a mosaic sheath of small spores outside the hair shaft, which is the fact that eliminates them. Epidermophyton does not invade hair at all, infecting only skin and nails.
Reference: Paniker's Textbook of Medical Parasitology and Mycology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.