A 7-year-old boy presents with patches of hair loss on the scalp dotted with broken-off hairs at the follicular openings. There is mild scaling but no inflammation. Culture grows Trichophyton tonsurans. What will Wood's lamp examination show?

• A No fluorescence of affected hairs ✓
• B Coral-red fluorescence of scales
• C Bright green fluorescence of affected hairs
• D Pale yellow fluorescence of scales

Explanation

Trichophyton tonsurans is the commonest cause of endothrix black-dot tinea capitis and does not fluoresce under Wood's lamp because it lacks pteridine production. Bright green fluorescence of hairs is characteristic of Microsporum species such as Microsporum canis and Microsporum audouinii. Therefore a negative Wood's lamp never excludes tinea capitis, and KOH or culture is required when suspicion persists.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.