A man develops rapidly progressive painful distal paraesthesiae, diffuse scalp alopecia with sparing of the outer third of the eyebrows, hyperkeratotic scaly skin lesions, and polyneuropathy. Hair microscopy shows blackened pigmented bands at the follicular base. Which antidote is specific?
- A Prussian blue (ferric ferrocyanide) ✓
- B Dimercaprol (BAL)
- C Calcium disodium EDTA
- D Penicillamine
Correct answer: A. Prussian blue (ferric ferrocyanide)
Explanation
Thallium poisoning classically combines painful peripheral neuropathy with alopecia that characteristically spares the inner two thirds of the eyebrows, plus the blackened hair follicle sign on microscopy. Prussian blue acts by exchanging potassium for thallium in the gut, interrupting enterohepatic circulation and increasing faecal excretion. BAL, EDTA and penicillamine chelate other metals and have no significant role in thallium toxicity.
Reference: The Essentials of Forensic Medicine and Toxicology, K.S. Narayan Reddy, 33rd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.