Correct Answer: b. Mydriasis
Mydriasis (pupil dilation) is NOT observed in organophosphate poisoning; instead, miosis (pupil constriction) is a hallmark muscarinic sign of cholinergic excess 1.
Why Each Option is Correct or Incorrect:
Option b (Mydriasis) - CORRECT ANSWER
Mydriasis is the opposite of what occurs in organophosphate poisoning. Organophosphates cause excessive acetylcholine accumulation at muscarinic receptors, leading to miosis (pupil constriction), not mydriasis 1, 2. Mydriasis would suggest anticholinergic toxicity, not cholinergic excess.
Option a (Diarrhea) - INCORRECT
Diarrhea IS observed in organophosphate poisoning. The muscarinic overstimulation causes increased gastrointestinal motility and secretions, leading to the classic "SLUDGE" syndrome (Salivation, Lacrimation, Urination, Defecation, Gastric cramps, Emesis), which explicitly includes diarrhea 1, 3, 4.
Option c (Miosis) - INCORRECT
Miosis IS a cardinal feature of organophosphate poisoning. Pupillary constriction results from muscarinic receptor overstimulation and is one of the most consistent clinical findings used to diagnose organophosphate toxicity 2, 3.
Option d (Bradycardia) - INCORRECT
Bradycardia IS observed in organophosphate poisoning. The excessive acetylcholine at cardiac muscarinic receptors causes parasympathetic overstimulation, leading to bradydysrhythmias and potential hemodynamic collapse 1, 5, 2.
Option e (Bronchospasm) - INCORRECT
Bronchospasm IS a life-threatening manifestation of organophosphate poisoning. Muscarinic receptor activation in bronchial smooth muscle causes bronchoconstriction, which along with excessive bronchial secretions (bronchorrhea), contributes to respiratory failure—a leading cause of death in these patients 1, 5.
Key Clinical Pitfall:
The distinguishing feature is remembering that organophosphates cause cholinergic excess (muscarinic and nicotinic overstimulation), producing miosis, NOT mydriasis. Mydriasis would suggest you're dealing with an anticholinergic toxidrome instead, which is the pharmacologic opposite.