On Wood's lamp examination of vitiligo lesions, the depigmented patches appear chalk-white and enhance. This is due to:
- A Increased collagen reflecting UV light
- B Complete absence of melanin allowing urocanic acid in the stratum corneum to fluoresce
- C Total absence of melanin pigment which acts as the normal UV absorber, unmasking fluorescence from dermal components ✓
- D Keratinocyte hypertrophy causing increased backscattering
Correct answer: C. Total absence of melanin pigment which acts as the normal UV absorber, unmasking fluorescence from dermal components
Explanation
Wood's lamp (365 nm UV-A) examination enhances the contrast of vitiligo patches. Melanin normally absorbs UV light; its complete absence in vitiligo patches removes this absorption. The residual fluorescence from urocanic acid and other naturally fluorescent compounds in the skin is then unmasked, making the patches appear brilliant white. This enhancement is most useful in fair-skinned individuals where clinical detection is difficult. Wood's lamp also helps distinguish complete from incomplete depigmentation (chemical leukoderma shows less fluorescence).
Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.