A 24-year-old woman presents with a pruritic, ring-shaped, scaly lesion on her inner thigh with central clearing. KOH mount of skin scraping shows septate hyphae and arthrospores. The organism responsible fluoresces under Wood's lamp. Which dermatophyte is most commonly responsible for this infection at this site?
- A Trichophyton rubrum
- B Epidermophyton floccosum ✓
- C Microsporum gypseum
- D Trichophyton tonsurans
Correct answer: B. Epidermophyton floccosum
Explanation
Tinea cruris (groin ringworm, 'jock itch') is most commonly caused by Epidermophyton floccosum and Trichophyton rubrum. Epidermophyton floccosum is notable for infecting skin and nails (but not hair) and is a common cause of tinea cruris and tinea pedis. T. rubrum is actually the most prevalent dermatophyte overall in tinea cruris; however, E. floccosum is classically emphasised as the cause. T. tonsurans is the leading cause of tinea capitis in children. Microsporum gypseum is a geophilic dermatophyte primarily causing tinea capitis.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.