A 30-year-old man working in an electronics recycling unit presents with rapidly progressive painful distal paresthesias, diffuse alopecia including loss of lateral eyebrows, and hyperhidrosis of palms and soles. Examination of plucked scalp hairs under polarized light shows darkly pigmented bands at the roots. The most likely poison is:
- A Arsenic
- B Thallium ✓
- C Mercury
- D Lead
Correct answer: B. Thallium
Explanation
Thallium classically causes painful peripheral neuropathy with dysesthesia plus total alopecia, and darkened (blackened) hair roots on microscopic examination due to melanin deposition. Arsenic also causes neuropathy and alopecia but its hair finding is transverse white bands (Mees' lines pattern in hair) rather than pigmented roots, which is the fact that separates the key from the best distractor. Mercury causes erethism and tremor, lead causes colic and basophilic stippling.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.