Toxicology: botulism mechanism: practice question

A Forensic Medicine question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Forensic Medicine · Toxicology: botulism mechanism

Sample item

Three family members have blurred vision, drooping eyelids, dilated pupils, difficulty swallowing and descending flaccid weakness a day after eating home-canned vegetables. They are afebrile and alert. What is the mechanism of the toxin?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Blocks release of acetylcholine at the nerve terminal

Botulinum toxin is a preformed toxin that cleaves SNARE proteins and prevents the release of acetylcholine from the motor nerve ending. The result is a descending symmetrical flaccid paralysis with cranial nerve involvement and autonomic features, with the patient alert and afebrile. Antitoxin and ventilatory support are the treatment.

Option by option

  • A. Blocks release of acetylcholine at the nerve terminal (correct)

    Correct. Blocked acetylcholine release gives flaccid paralysis with autonomic signs.

  • B. Inhibits acetylcholinesterase at the synapse

    Acetylcholinesterase inhibition is the mechanism of organophosphates and causes cholinergic excess.

  • C. Blocks sodium channels in the axon

    Sodium channel blockade is the mechanism of tetrodotoxin.

  • D. Antagonises glycine receptors in the spinal cord

    Glycine receptor antagonism is the mechanism of strychnine, which produces spasms.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is A, Blocks release of acetylcholine at the nerve terminal. Botulinum toxin is a preformed toxin that cleaves SNARE proteins and prevents the release of acetylcholine from the motor nerve ending.

Why is "Inhibits acetylcholinesterase at the synapse" not the answer?

Acetylcholinesterase inhibition is the mechanism of organophosphates and causes cholinergic excess.

Why is "Blocks sodium channels in the axon" not the answer?

Sodium channel blockade is the mechanism of tetrodotoxin.

Why is "Antagonises glycine receptors in the spinal cord" not the answer?

Glycine receptor antagonism is the mechanism of strychnine, which produces spasms.

What concept does this question test?

It tests Toxicology: botulism mechanism in Forensic Medicine. The result is a descending symmetrical flaccid paralysis with cranial nerve involvement and autonomic features, with the patient alert and afebrile. Antitoxin and ventilatory support are the treatment.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Toxicology: botulism mechanism?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.