KMU Past Paper Practice
Organophosphate, Nerve-Gas and Mushroom Poisoning
3rd Year MBBS • 20 A-Type Single Best Answer MCQs
MCQ 1
A 36-year-old pesticide sprayer develops profuse sweating, salivation and abdominal cramps after accidental organophosphate exposure. A student is surprised that sweating is prominent despite sweat glands receiving sympathetic innervation. Which physiological feature best explains this finding?
Sympathetic fibers to sweat glands release acetylcholine
Postganglionic sympathetic fibers supplying sweat glands are cholinergic. Acetylcholine accumulation therefore produces marked sweating despite sympathetic innervation.
MCQ 2
A 28-year-old man with pesticide poisoning is receiving atropine. His chest becomes clearer and oxygenation improves, but his pupils remain markedly constricted. Which interpretation is most appropriate?
Improved respiratory secretions are more important than normalization of pupils
The immediate life-saving effect of atropine is reduction of bronchial secretions and bronchoconstriction. Persistent miosis alone does not indicate inadequate respiratory muscarinic control.
MCQ 3
A farm worker is brought after a concentrated organophosphate pesticide spilled over his clothes and skin. He is conscious but develops sweating and increasing salivation during transport. Which early measure most directly limits continuing absorption?
Remove contaminated clothing and decontaminate exposed skin
Dermal organophosphate exposure can continue while contaminated clothing and liquid remain on the body. Early external decontamination reduces further absorption.
MCQ 4
During a toxicology discussion, students are asked to identify an organophosphate developed primarily as a nerve agent rather than as an agricultural insecticide. Which compound best fits this description?
VX
VX is a highly potent organophosphate nerve agent. The remaining compounds listed are encountered primarily as organophosphate insecticides.
MCQ 5
A poisoned agricultural worker is treated with atropine and a cholinesterase-regenerating drug. The examiner asks for another compound belonging to the same antidotal class as pralidoxime. Which is the best answer?
Obidoxime
Obidoxime, like pralidoxime, belongs to the oxime group of cholinesterase-regenerating compounds used in organophosphate poisoning.
MCQ 6
A 40-year-old man with confirmed organophosphate poisoning has miosis and bronchorrhea but is found to have a pulse of 108/min rather than bradycardia. Which explanation best accounts for this apparent inconsistency?
Ganglionic and mixed autonomic effects can make heart rate variable
Organophosphate toxicity affects muscarinic and nicotinic autonomic sites simultaneously. Heart rate may therefore vary rather than showing obligatory bradycardia.
MCQ 7
A severely poisoned patient has already received appropriate antidotal therapy but remains hypoventilated because of respiratory muscle weakness and depressed consciousness. Which intervention is most important at this stage?
Provide assisted ventilation and respiratory support
Antidotes do not replace supportive care. Persistent hypoventilation from neuromuscular and central effects requires direct respiratory support.
MCQ 8
At autopsy of a man suspected to have died from pesticide poisoning, the lungs are congested and edematous and frothy material fills the major airways. Why should these findings be interpreted cautiously?
They are supportive findings but are not specific to one poison
Pulmonary congestion, edema and frothy secretions support severe cholinergic poisoning but can occur in other conditions, so forensic interpretation requires corroboration.
MCQ 9
Two patients ingest similar volumes of different organophosphate formulations. One dies rapidly while the other survives after prompt treatment. Which factor best explains why a single fatal period cannot be applied to the whole group?
Clinical course varies with compound potency, exposure severity and treatment
Different organophosphates vary markedly in toxicity, and outcome is strongly influenced by absorbed amount and speed of supportive and antidotal treatment.
MCQ 10
A chemical-warfare casualty develops severe cholinergic toxicity after exposure to an unknown agent. Which additional compound, if identified at the scene, would belong to the same nerve-agent group as sarin and soman?
Tabun
Tabun is an organophosphate nerve agent, whereas malathion, diazinon, chlorpyrifos and dimethoate are primarily insecticides.
MCQ 11
A patient with organophosphate poisoning reaches hospital late. The clinician explains that newly synthesized acetylcholinesterase may eventually be required for full recovery of enzyme function. Which event would make this explanation most relevant?
Aging of phosphorylated acetylcholinesterase
Aging produces a highly stable inhibited enzyme complex that is poorly responsive to oxime reactivation, making recovery dependent on restoration of functional enzyme.
MCQ 12
A soldier received pyridostigmine before entering an area with anticipated nerve-agent exposure. He remains unexposed and the drug is later withdrawn. What allows previously protected acetylcholinesterase molecules to regain activity?
Spontaneous reversal of reversible carbamylation
Pyridostigmine temporarily carbamylates acetylcholinesterase. Subsequent decarbamylation restores functional enzyme because the interaction is reversible.
MCQ 13
A patient with acute organophosphate poisoning has fasciculations that progress to flaccid weakness. Which sequence best explains this change at the neuromuscular junction?
Persistent nicotinic stimulation followed by impaired neuromuscular transmission
Excess acetylcholine initially overstimulates nicotinic receptors, producing fasciculations; persistent stimulation later interferes with effective neuromuscular transmission and causes weakness.
MCQ 14
A 52-year-old man presents with severe cholinergic poisoning after ingesting a farm chemical. Which history would most strongly support exposure to an organophosphate insecticide rather than a nerve agent?
Access to a chlorpyrifos-containing agricultural preparation
Chlorpyrifos is primarily an agricultural organophosphate insecticide, whereas VX, sarin, soman and tabun are nerve agents.
MCQ 15
Several hours after eating wild mushrooms, a 24-year-old woman has repeated vomiting and watery diarrhea with clinical dehydration but no salivation, miosis or bronchorrhea. Which management principle is most appropriate initially?
Correct fluid and electrolyte losses while assessing the toxin syndrome
Mushroom poisoning is toxin-dependent. Significant gastrointestinal losses require supportive fluid and electrolyte correction while the clinical syndrome is further assessed.
MCQ 16
A man eats unidentified wild mushrooms and soon develops salivation, lacrimation, wheezing, abdominal cramps and bradycardia without muscle fasciculations. Which pharmacological target is most appropriate for immediate symptomatic treatment?
Muscarinic acetylcholine receptors
This pattern is compatible with muscarinic mushroom toxicity. Atropine acts by competitively antagonizing muscarinic receptors and reduces these manifestations.
MCQ 17
A patient with mushroom poisoning develops agitation, altered perception and confusion but has no prominent secretory or cardiovascular cholinergic findings. Which conclusion is most appropriate?
Different mushroom toxins can produce predominantly neurological syndromes
Mushroom poisoning is not one uniform toxidrome. Some toxins produce CNS manifestations such as confusion, agitation, altered perception or seizures.
MCQ 18
An unconscious patient with organophosphate poisoning has copious secretions and weak respiratory effort. Atropine and an oxime are available. Which management sequence best reflects the immediate priorities?
Support airway and ventilation while providing appropriate antidotal therapy
Severe poisoning requires immediate stabilization of airway and breathing together with atropine and an appropriate oxime; antidotes do not substitute for ventilation.
MCQ 19
A forensic examiner reviews a fatal pesticide case. Toxicology confirms an organophosphate, but the available information does not establish whether exposure was accidental, suicidal or homicidal. Which conclusion is most appropriate?
The poison identifies the cause of toxicity but not the manner of exposure by itself
Toxicological identification supports the poisoning diagnosis, but manner requires correlation with scene, history and other medico-legal evidence.
MCQ 20
A clinician compares two poisoned patients. One has organophosphate exposure with weakness and bronchorrhea; the other has gastrointestinal symptoms after mushroom ingestion without a defined toxidrome. Which therapeutic principle best distinguishes their management?
Organophosphate therapy targets cholinergic excess, whereas mushroom treatment depends on the toxin syndrome
Organophosphate toxicity has a defined cholinergic mechanism with specific antidotal therapy, while mushroom poisoning varies by toxin and requires syndrome-directed management.