A 32-year-old industrial worker develops excruciating burning pain in the feet and distal weakness over 4 weeks. He then notices rapid shedding of scalp hair, axillary and limb hair, and loss of the lateral two-thirds of his eyebrows. There is hyperkeratosis of the palms. Hair analysis is planned. Which additional finding would MOST strongly point to thallium rather than arsenic as the culprit?
- A Rain-drop hyperpigmentation over the trunk
- B Diffuse non-scarring alopecia with relative sparing of the inner third of the eyebrows ✓
- C Palmoplantar punctate keratoses
- D Transverse white bands across all fingernails
Correct answer: B. Diffuse non-scarring alopecia with relative sparing of the inner third of the eyebrows
Explanation
Thallium characteristically attacks rapidly growing hair follicles, producing diffuse non-scarring alopecia with classical sparing of the medial third of the eyebrows, along with extremely painful distal neuropathy. Rain-drop pigmentation and palmoplantar keratoses are hallmarks of chronic arsenicism, so options A and C argue against thallium. Mees-type transverse nail bands occur in both poisons and therefore cannot discriminate between them.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.