A 6-year-old girl is brought with intense scalp itching. On examination, small white oval structures are seen attached to the hair shafts close to the scalp. Which feature best distinguishes true nits from hair casts (pseudonits)?
- A Nits are firmly cemented to the hair shaft, while hair casts slide freely along it ✓
- B Nits are yellow-white, while hair casts are pearly white
- C Nits are found only at the hair tip, while hair casts are near the scalp
- D Nits fluoresce under Wood's lamp, while hair casts do not
Correct answer: A. Nits are firmly cemented to the hair shaft, while hair casts slide freely along it
Explanation
Nits are firmly cemented to the hair shaft with a tough proteinaceous cement secreted by the louse, making them difficult to remove. Hair casts (pseudonits) are remnants of the root sheath that encircle the hair shaft and slide freely along it. This distinction is the most reliable clinical differentiator. Color and fluorescence are unreliable distinguishing features.
Reference: Andrews' Diseases of the Skin, 13th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.