Two patients present with painful peripheral neuropathy and alopecia. In patient X, examination of plucked hairs under light microscopy shows a band of dark pigmentation at the base of the hair shaft. In patient Y there is raindrop pigmentation of skin and transverse white bands across all nails. Patients X and Y have been poisoned respectively by:

• A Arsenic and thallium
• B Thallium and arsenic ✓
• C Mercury and lead
• D Thallium and mercury

Explanation

Thallium concentrates in the hair root, producing a characteristic dark band at the base of the hair shaft on microscopy, along with painful neuropathy and alopecia. Arsenic causes raindrop pigmentation of skin and transverse white bands (Mees' lines) on nails. Both metals cause neuropathy and hair loss, so the hair root band versus nail bands and raindrop pigmentation is the discriminating finding.

Reference: Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology, 7th ed.

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