Sunday, July 19, 2009

Question 13

65 year old farmer was brought to the hospital by his wife at midnight. She says he is having severe headache since last 8 hours after he returned from work. He is sweating a lot and tears are falling from his eyes. He says he is feeling weak and tired and has vomited once. The vomitus just contains what he has eaten in the evening and there was no blood. On examination his skin is cool and wet. His BP is 124/82 mm Hg and Pulse is 64/min. He appears to be confused and answers only a few questions. During the interview, he was repeatedly spitting in the thrash bin in the ER. Systemic examination is non significant, except his pupils are smaller and few twitches can be seen in his limb muscles. He is diagnosed as insecticide toxicity and atropine is administered. What is the mechanism of action of the toxin?

A) Blocks Acetylcholine receptor at the post synaptic membrane
B) Stimulates Acetylcholine receptor at the post synaptic membrane
C) Blocks the enzymes that produce choline & Acetate in the synapse
D) Blocks the reuptake of choline in the presynaptic membrane
E) Block release of Acetylcholine
F) Blocks the Ryanodine receptors
G) Blocks the enzyme that metabolizes Catecholamines after uptake in the presynapse

1 comments:

Usmle Challenger July 20, 2009 at 12:46 AM  

Answer: C) Blocks the enzyme that produces choline and Acetate in the synapse.

The vignette describes a case of insecticide (Organophosphate Poisoning). The usual presenting symptoms are headache, abdominal cramping, and etcetera.
Classic symptoms can be memorized as mnemonic SLUDGE & M
Salivation
Lacrimation
Urinary incontinence
Defecation
GI upset
Emesis &
Miosis
These compounds are potent nerve agents and function by inhibiting acetylcholinesterase (AChE) enzyme which metabolize Acetylcholine into Choline and acetate.
Treatment consists of Atropine & Pralidoxime.

Other Options:
A) Blocks Acetylcholine receptor at the post synaptic membrane: Anticholinergic
B) Stimulates Acetylcholine receptor at the post synaptic membrane: Ca+2
E) Block release of Acetylcholine: Botulinum
F) Blocks the Ryanodine receptors: Dantrolene
G) Blocks the enzyme that metabolizes Catecholamines after uptake in the presynapse: MAOI

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