Six hours after eating reef fish at a coastal resort, a 40-year-old man develops vomiting, diarrhoea, and then complains that cold water feels hot to his hands and hot tea feels cold. The toxin responsible acts by:

• A Blocking voltage-gated sodium channels at the node of Ranvier
• B Irreversibly inhibiting acetylcholinesterase
• C Blocking acetylcholine release at the neuromuscular junction
• D Opening voltage-gated sodium channels in neuronal membranes ✓

Explanation

This is ciguatera poisoning from reef fish such as grouper and barracuda. Ciguatoxin binds to voltage-gated sodium channels and holds them open, causing neuronal hyperexcitability, which explains the pathognomonic reversal of temperature sensation along with gastrointestinal and neurological features. Tetrodotoxin and saxitoxin block sodium channels instead, and organophosphates inhibit cholinesterase, none of which produce temperature reversal.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.