Question

A 28-year-old male develops muscarinic toxicity following consumption of a mushroom. Which clinical manifestation is expected?

• A. Tachycardia
• B. Mydriasis
• C. Bradycardia
• D. Urinary retention

Hint:

Muscarinic excess means parasympathetic overactivity, so think of a slow heart rate and small pupils.

Answer 1

The Correct Option is C

Step 1: Understand the poisoning:
Some mushrooms, such as Inocybe and Clitocybe species, contain muscarine. Muscarine is a direct agonist at muscarinic acetylcholine receptors.
It is not broken down by acetylcholinesterase, so its action lasts for hours. The patient shows features of excess parasympathetic stimulation (a cholinergic picture).

Step 2: Recall the effects of muscarinic stimulation:
Every organ with muscarinic receptors responds. The eye shows miosis (small pupil) and spasm of accommodation.
Glands give excess salivation, sweating, lacrimation and bronchial secretions. The lung shows bronchoconstriction.
The gut shows cramps, vomiting and diarrhoea. The bladder wall contracts and the sphincter relaxes, so there is urgency and incontinence.
The heart shows a fall in heart rate, because M2 receptors on the SA node slow the rate. This is bradycardia.

Step 3: Pick the expected finding:
Among the options, only bradycardia fits this picture. So option (C) is correct.
The usual antidote is atropine, which blocks the muscarinic receptors.

Step 4: Check option (A) Tachycardia:
A fast heart rate is a sign of vagal blockade, which happens with atropine or other anticholinergic drugs. Muscarine does the opposite. So (A) is wrong.

Step 5: Check option (B) Mydriasis:
Mydriasis (wide pupil) is caused by blocking the muscarinic receptor of the sphincter pupillae. Muscarinic toxicity gives miosis, not mydriasis. So (B) is wrong.

Step 6: Check option (D) Urinary retention:
Retention of urine is a feature of anticholinergic toxicity, because the detrusor muscle relaxes. In muscarinic toxicity the detrusor contracts, so the patient passes urine often or loses control. So (D) is wrong.

Final Answer:
Muscarinic toxicity from a mushroom produces bradycardia. This is option (C).