Correct Answer: B. Datura
Datura poisoning presents with a classic anticholinergic toxidrome characterized by the triad of mydriasis (dilated pupil), dry skin, and altered mental status. Datura species (Datura stramonium, D. inoxia) contain tropane alkaloids—scopolamine, hyoscyamine, and atropine—which competitively block muscarinic acetylcholine receptors. The dry, dilated pupil results from unopposed sympathetic activity and loss of parasympathetic tone. Dry skin reflects inhibition of sweat glands. Slurred speech and altered sensorium occur due to central anticholinergic effects on the CNS. In India, Datura poisoning is common in rural areas where the plant grows as a weed; seeds are sometimes ingested accidentally or intentionally. The presentation fits the mnemonic "Red as a beet, dry as a bone, blind as a bat, mad as a hatter"—all anticholinergic signs. Management includes supportive care and physostigmine (a cholinesterase inhibitor that crosses the blood-brain barrier) in severe cases. The combination of mydriasis + dry skin + altered sensorium is pathognomonic for anticholinergic poisoning, and Datura is the most common plant source in the Indian subcontinent.
Why the other options are wrong
A. Cannabis — Cannabis causes miosis (pinpoint pupils), not mydriasis, and produces conjunctival injection (red eyes). While it causes altered sensorium and dry mouth, the pupillary finding is opposite to Datura. Cannabis is a sympathomimetic CNS stimulant, not an anticholinergic agent. The dry pupil (dilated) is the key discriminator here. C. Alcohol — Alcohol poisoning causes constricted or normal pupils, not dilated pupils. While it causes altered sensorium and slurred speech, it does not produce the characteristic dry skin and mydriasis seen in anticholinergic poisoning. Alcohol is a CNS depressant affecting GABA receptors, not muscarinic receptors. D. Morphine — Morphine causes pinpoint pupils (miosis), the opposite of the dilated pupil described. While it causes altered sensorium, it produces wet skin (diaphoresis) and increased salivation due to opioid receptor activation, not the dry skin characteristic of anticholinergic poisoning. Opioid toxidrome is distinct from anticholinergic toxidrome.
High-Yield Facts
- Anticholinergic toxidrome = mydriasis + dry skin + dry mouth + altered sensorium + tachycardia + hyperthermia (mnemonic: 'Red, Dry, Blind, Mad').
- Datura alkaloids (scopolamine, hyoscyamine, atropine) block muscarinic M1–M5 receptors, causing unopposed sympathetic effects.
- Physostigmine (not atropine) is the antidote for Datura poisoning because it crosses the blood-brain barrier and reverses both peripheral and central anticholinergic effects.
- Mydriasis vs. miosis: Datura = dilated pupils; Cannabis, morphine, alcohol = normal/constricted pupils—this is the key discriminator in toxicology MCQs.
- Indian epidemiology: Datura poisoning is common in rural India due to accidental ingestion of seeds or intentional use; it is a leading cause of plant poisoning in forensic cases.
Mnemonics
Anticholinergic Toxidrome (Red, Dry, Blind, Mad) Red as a beet (flushed skin, tachycardia), Dry as a bone (dry skin, dry mouth, anhidrosis), Blind as a bat (mydriasis, cycloplegia), Mad as a hatter (altered sensorium, agitation, hallucinations). Use this when you see mydriasis + dry skin + CNS changes. Pupil Clues in Toxicology DAMP = Datura/Anticholinergics = Mydriasis (dilated); SLUDGE = Sympathomimetics/Stimulants = normal/dilated; PINPOINT = Opioids/Organophosphates = Miosis (constricted). Pupil size is the fastest discriminator.
NBE Trap
NBE pairs dilated pupil with altered sensorium to trap students who confuse anticholinergic poisoning (Datura) with sympathomimetic poisoning (cocaine, amphetamines). The key is recognizing that dry skin + mydriasis + slurred speech = anticholinergic, not sympathomimetic. Alcohol and morphine are included as distractors because they also cause altered sensorium, but their pupillary findings are opposite.
Clinical Pearl
In Indian emergency departments, Datura poisoning is a common presentation in rural admissions, especially during monsoon when the plant thrives. Early recognition of the anticholinergic triad (mydriasis, dry skin, altered sensorium) allows rapid diagnosis and initiation of physostigmine therapy, which can be life-saving in severe cases with respiratory depression or cardiac arrhythmias.
_Reference: Forensic Medicine & Toxicology (Reddy, 34th ed.) Ch. 24 (Plant Poisons); Parikh's Textbook of Medical Jurisprudence, Forensic Medicine & Toxicology (7th ed.) Ch. 15 (Poisoning)_