A 2-year-old with brittle, sulfur-deficient hair, ichthyosis, intellectual disability and decreased fertility undergoes hair microscopy. Under polarised light, the hair shafts show alternating light and dark bands. This finding, called tiger-tail banding, is characteristic of:
- A Menkes disease
- B Monilethrix
- C Trichothiodystrophy ✓
- D Netherton syndrome
Correct answer: C. Trichothiodystrophy
Explanation
Trichothiodystrophy involves sulfur-deficient hair due to reduced cystine-rich matrix proteins, producing tiger-tail banding on polarised microscopy. Mutations affect NER genes such as ERCC2/XPD, yet unlike xeroderma pigmentosum there is no increased skin cancer risk despite shared repair defects. Monilethrix shows beaded hair with elliptical nodes, Menkes shows pili torti, and Netherton shows trichorrhexis invaginata (bamboo hair) with elevated IgE, each distinguishable microscopically.
Reference: Rook's Textbook of Dermatology, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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