A child from a rural family presents with patches of scalp hair loss studded with yellowish, cup-shaped crusts (scutula) that are matted to the scalp and give off a mousy odour. Direct microscopy of plucked hairs shows hyphae and air spaces within the hair shafts. The most likely causative dermatophyte is:
- A Microsporum canis
- B Microsporum audouinii
- C Trichophyton schoenleinii ✓
- D Epidermophyton floccosum
Correct answer: C. Trichophyton schoenleinii
Explanation
Favus, the most severe form of tinea capitis, presents with scutula, yellowish cup-shaped crusted lesions with a characteristic mousy smell. It is caused by Trichophyton schoenleinii, an endothrix fungus that invades the hair shaft itself, producing air spaces visible microscopically. Microsporum canis and M. audouinii are ectothrix species producing spores on the outside of the shaft, and Epidermophyton floccosum infects skin and nails but never hair.
Reference: Fitzpatrick's Dermatology, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.