Forensic Toxicology — MCQs

Forensic Toxicology Indian Medical PG Practice Questions and MCQs

Question 41: In which of the following poisonings is emesis not contraindicated?

A. Kerosene poisoning
B. Nux vomica poisoning
C. Oxalic acid poisoning
D. Arsenic poisoning (Correct Answer)

Explanation: **Explanation:** In forensic toxicology, the decision to induce emesis (or perform gastric lavage) depends on the risk of secondary injury during the act of vomiting. **Why Arsenic is the correct answer:** Arsenic is a **non-corrosive, non-volatile metallic irritant**. It does not damage the esophageal mucosa upon re-exposure during vomiting, nor does it pose a high risk of aspiration pneumonitis. Therefore, emesis is **not contraindicated** and is often encouraged in the early stages of acute poisoning to remove the unabsorbed toxin from the stomach. **Why the other options are contraindicated:** * **Kerosene (Hydrocarbons):** These have low viscosity and high volatility. Inducing emesis carries a massive risk of **aspiration pneumonitis**, which is more lethal than the systemic effects of the poison itself. * **Nux Vomica (Strychnine):** This is a potent spinal stimulant. Any sensory stimulus, including the act of gagging or vomiting, can precipitate **violent tetanic convulsions** and opisthotonus, leading to respiratory failure. * **Oxalic Acid (Corrosives):** Corrosives cause "liquefactive" or "coagulative" necrosis. Inducing emesis re-exposes the esophagus to the acid, increasing the risk of **perforation** and chemical burns. **High-Yield Clinical Pearls for NEET-PG:** * **General Contraindications for Emesis:** Corrosives, Hydrocarbons, Comatose patients (risk of aspiration), and Convulsant poisonings. * **Arsenic Presentation:** Look for "Rice water stools" (mimicking Cholera) and "Garlicky breath." * **Antidote of Choice:** BAL (British Anti-Lewisite) or DMSA (Succimer). * **Vomitus in Arsenic:** Often contains streaks of blood due to severe gastrointestinal irritation (sub-endocardial hemorrhages are a classic autopsy finding).

Question 42: Rectified spirit is NOT used as a preservative in the case of:

A. Phenol (Correct Answer)
B. Cyanide
C. Insecticides
D. Alphos

Explanation: In forensic toxicology, the choice of preservative for viscera is critical to prevent the degradation of poisons or interference with chemical analysis. **Why Phenol is the Correct Answer:** Rectified spirit (95% ethyl alcohol) is the standard preservative for most viscera. However, it is strictly contraindicated in cases of **Phenol (Carbolic acid)** poisoning. This is because phenol is highly soluble in alcohol. Using rectified spirit would dissolve the phenol, making its extraction and quantification during chemical analysis extremely difficult. For phenol poisoning, **saturated saline** is the preferred preservative. **Analysis of Incorrect Options:** * **Cyanide:** Rectified spirit is the preservative of choice. While some sources suggest it may slightly inhibit certain reactions, it is standard practice. (Note: Saturated saline is avoided here as it may hasten the conversion of cyanide to thiocyanate). * **Insecticides (Organophosphates):** Rectified spirit is used to preserve viscera in these cases. It prevents the enzymatic hydrolysis of the toxin. * **Alphos (Aluminum Phosphide):** Rectified spirit is used. It helps preserve the tissues for the detection of phosphine gas or its metabolites. **High-Yield Clinical Pearls for NEET-PG:** * **General Rule:** Saturated saline is used for most poisons EXCEPT corrosive acids and salts of heavy metals (where it may cause chemical reactions). * **The "Alcohol Exception":** Rectified spirit is used for almost all poisons **EXCEPT** Alcohol, Phenol, Chloral hydrate, Chloroform, and Ether (as these are soluble in or related to alcohol). * **Preservative for Blood:** Sodium fluoride (10 mg/ml) is used, especially for alcohol estimation, as it inhibits glycolysis and prevents neo-formation of alcohol by bacteria.

Question 43: Chocolate brown postmortem staining is seen in which type of poisoning?

A. Potassium cyanide poisoning (Correct Answer)
B. Opium poisoning
C. Hydrogen sulfide poisoning
D. Cyanide poisoning

Explanation: **Explanation:** Postmortem staining (livor mortis) typically appears bluish-purple. However, specific poisons alter the color of hemoglobin, leading to characteristic changes in staining. **1. Why Potassium Chlorate is Correct:** The question contains a common typographical error often seen in exams; while the option says "Potassium cyanide," the classic cause of **chocolate brown** staining is actually **Potassium chlorate** (or Nitrites/Aniline). These are strong oxidizing agents that convert hemoglobin into **methemoglobin**. Methemoglobin is dark brown, giving the skin and blood a characteristic chocolatey appearance. *(Note: If the option intended was Potassium Chlorate, it is the classic answer. If the examiner specifically links Cyanide to this color, it is often a distractor or a specific variant of "Potassium" salt poisoning leading to methemoglobinemia).* **2. Analysis of Other Options:** * **Cyanide Poisoning:** Classically produces **bright cherry-red** postmortem staining. This occurs because cyanide inhibits cytochrome oxidase, preventing tissues from utilizing oxygen. Consequently, the venous blood remains highly oxygenated (oxyhemoglobin). * **Opium Poisoning:** Produces **deep lividity** (bluish-black) due to asphyxia and secondary respiratory depression, leading to increased reduced hemoglobin. * **Hydrogen Sulfide Poisoning:** Can produce a **bluish-green** discoloration due to the formation of sulfhemoglobin. **High-Yield Clinical Pearls for NEET-PG:** * **Cherry Red:** Carbon Monoxide (Carboxyhemoglobin). * **Bright Red/Pink:** Cyanide, Cold exposure. * **Chocolate Brown:** Potassium chlorate, Nitrites, Aniline, Nitrobenzene (Methemoglobinemia). * **Dark Blue/Black:** Opium, Asphyxial deaths. * **Greenish:** Hydrogen sulfide.

Question 44: A 35-year-old man was found unconscious. Examination revealed bilateral constricted pupils, bradycardia, excessive sweating, and secretions. What is the most likely cause?

A. Opium poisoning
B. Acute alcohol intoxication
C. Organophosphorous poisoning (Correct Answer)
D. Pontine hemorrhage

Explanation: **Explanation:** The clinical presentation of **bilateral constricted pupils (miosis)**, **bradycardia**, and **excessive secretions** (sweating, salivation, lacrimation) points toward a **cholinergic crisis**, which is the hallmark of **Organophosphorous (OP) poisoning**. **1. Why Organophosphorous Poisoning is Correct:** OP compounds inhibit the enzyme **Acetylcholinesterase**, leading to an accumulation of Acetylcholine at the synapses. This results in overstimulation of: * **Muscarinic receptors:** Causing the "SLUDGE" syndrome (Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis) plus **Miosis**, **Bradycardia**, and **Bronchospasm**. * **Nicotinic receptors:** Leading to muscle fasciculations and weakness. The presence of "excessive sweating and secretions" is the key differentiator here, as OP poisoning is a "wet" presentation. **2. Why Other Options are Incorrect:** * **Opium Poisoning:** While it presents with "pinpoint" pupils and respiratory depression, it typically causes **dry skin and mouth** and decreased bowel sounds, unlike the "wet" presentation of OP poisoning. * **Acute Alcohol Intoxication:** Usually presents with **dilated pupils** (or normal), tachycardia, and ataxia. It does not cause excessive secretions. * **Pontine Hemorrhage:** This also presents with **pinpoint pupils** and coma, but it is usually associated with **hyperpyrexia** (high fever) and rapid, irregular breathing, rather than the generalized cholinergic secretions seen here. **High-Yield Clinical Pearls for NEET-PG:** * **Antidote of choice:** **Atropine** (reverses muscarinic effects; titrated until secretions dry up) and **Pralidoxime/PAM** (reactivates cholinesterase if given early). * **Diagnostic sign:** Garlic-like odor from the mouth or vomitus. * **Key mnemonic:** **DUMBELS** (Defecation, Urination, Miosis, Bronchospasm/Bradycardia, Emesis, Lacrimation, Salivation).

Question 45: Organophosphorus compounds exert their effects by which of the following mechanisms?

A. Stimulating acetylcholinesterase
B. Inhibiting acetylcholinesterase (Correct Answer)
C. Blocking acetylcholinesterase receptors
D. None of the above

Explanation: **Mechanism of Action: Organophosphorus (OP) Compounds** **Explanation of the Correct Answer (B):** Organophosphorus compounds act as potent **irreversible inhibitors of the enzyme Acetylcholinesterase (AChE)**. Under normal physiological conditions, AChE is responsible for breaking down the neurotransmitter Acetylcholine (ACh) into choline and acetic acid at the synaptic cleft. OP compounds bind to the active site (serine hydroxyl group) of the enzyme, forming a stable phosphoryl-enzyme complex. This inhibition leads to the **accumulation of Acetylcholine** at muscarinic and nicotinic receptors, resulting in a "cholinergic crisis." **Why Other Options are Incorrect:** * **Option A:** Stimulating AChE would lead to a rapid depletion of acetylcholine, which is the opposite of the clinical presentation of OP poisoning (miosis, secretions, bradycardia). * **Option C:** OP compounds do not block receptors; they increase the concentration of the ligand (ACh) that acts on those receptors. Drugs like Atropine are the ones that block receptors (muscarinic). **High-Yield Clinical Pearls for NEET-PG:** * **Aging of Enzyme:** Initially, the OP-AChE bond can be broken by Oximes (Pralidoxime). However, after a period (minutes to hours), the bond becomes permanent through a process called "aging," after which Oximes are no longer effective. * **Clinical Features:** Remember the mnemonic **DUMBELS** (Diarrhea, Urination, Miosis, Bronchospasm/Bradycardia, Emesis, Lacrimation, Salivation). * **Management:** * **Atropine:** Specific antidote (physiological antagonist) that blocks muscarinic effects. Titrated until "Atropinization" (clear lungs, heart rate >80 bpm). * **Pralidoxime (2-PAM):** Cholinesterase regenerator; must be given before "aging" occurs. * **Post-mortem Finding:** Characteristic **kerosene-like or garlic-like odor** from the mouth and stomach contents.

Question 46: A 45-year-old patient develops nausea, vomiting, and ascending paralysis upon ingestion of broken seeds from a plant. What is the most likely active compound present in these seeds?

A. Atropine
B. Strychnine (Correct Answer)
C. Ricin
D. Bhilawanol

Explanation: ### Explanation **Correct Option: B. Strychnine** Strychnine is the active alkaloid found in the seeds of *Strychnos nux-vomica*. The seeds are extremely hard and must be crushed or broken to release the toxin. * **Mechanism:** Strychnine acts as a potent competitive antagonist of **glycine**, an inhibitory neurotransmitter, at the postsynaptic receptor sites in the spinal cord. * **Clinical Presentation:** Loss of inhibition leads to excessive motor neuron activity. This manifests as **ascending paralysis** (starting from the lower limbs and moving upwards) followed by violent, tetanic convulsions. Characteristically, these convulsions are triggered by minimal sensory stimuli (touch, light, or sound). **Why other options are incorrect:** * **A. Atropine:** Found in *Datura stramonium*. It causes anticholinergic symptoms: "Dry as a bone, red as a beet, blind as a bat, hot as a hare, and mad as a hatter." It does not cause ascending paralysis or spinal convulsions. * **C. Ricin:** Found in *Ricinus communis* (Castor seeds). It is a potent cytotoxin (toxalbumin) that causes severe gastroenteritis, mucosal sloughing, and multi-organ failure, but not the specific neuro-muscular pattern of strychnine. * **D. Bhilawanol:** Found in *Semecarpus anacardium* (Marking nut). It is a local irritant causing blistering and dermatitis; systemic ingestion leads to gastrointestinal irritation and hypotension. **High-Yield Clinical Pearls for NEET-PG:** * **Opisthotonus:** A characteristic backward arching of the body seen in Strychnine poisoning (similar to Tetanus). * **Risus Sardonicus:** A fixed, grinning expression due to spasm of facial muscles. * **Differentiation from Tetanus:** In Strychnine poisoning, muscles relax completely between convulsions, and the onset is sudden. In Tetanus, muscle rigidity is persistent. * **Post-mortem finding:** Early onset and disappearance of rigor mortis (due to rapid ATP depletion from convulsions).

Question 47: In low concentrations of carbon monoxide, what is the commonest symptom?

A. Nausea
B. Headache
C. Muscular weakness
D. None of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **None of the above** because, at very low concentrations of Carbon Monoxide (CO), the condition is typically **asymptomatic**. Carbon monoxide has an affinity for hemoglobin that is 200–250 times greater than oxygen, forming **Carboxyhemoglobin (COHb)**. Symptoms only manifest once COHb levels reach a specific threshold: * **0–10% COHb:** Usually asymptomatic (common in heavy smokers). * **10–20% COHb:** The earliest clinical symptom to appear is a **tightness across the forehead** or a **mild headache**. * **20–30% COHb:** Throbbing headache and dizziness. **Why other options are incorrect:** * **Headache (B):** While headache is the *first* clinical symptom of CO poisoning, it occurs at mild-to-moderate concentrations (10–20% COHb), not at "low" (sub-clinical) concentrations. * **Nausea (A) and Muscular Weakness (C):** These are features of moderate-to-severe toxicity. Nausea typically occurs at 20–30% COHb, while muscular weakness (often preventing the victim from escaping the source) occurs at 30–40% COHb. **High-Yield Clinical Pearls for NEET-PG:** * **Cherry Red Discoloration:** A classic finding in CO poisoning (due to COHb), seen in the skin, mucous membranes, and post-mortem lividity. * **CT/MRI Finding:** Bilateral necrosis of the **Globus Pallidus** is a pathognomonic radiological feature. * **Treatment:** 100% Hyperbaric Oxygen (HBO) is the treatment of choice to reduce the half-life of COHb. * **Mechanism:** It causes a **left shift** in the Oxygen-Dissociation Curve, inhibiting oxygen release to tissues.

Question 48: Which of the following poisons is associated with the development of Acrodynia?

A. Mercury (Correct Answer)
B. Oxalic acid
C. Phenolic acid
D. Carbolic acid

Explanation: **Explanation:** **Acrodynia** (also known as **Pink Disease** or Swift’s disease) is a classic hypersensitivity reaction seen primarily in children following chronic exposure to **Mercury** (Option A). It is characterized by a "pinkish" discoloration of the hands and feet, accompanied by painful swelling, desquamation, tachycardia, and profuse sweating. The underlying mechanism involves mercury’s interference with the metabolic pathways of catecholamines, leading to an excess of epinephrine and subsequent peripheral vasoconstriction. **Analysis of Incorrect Options:** * **Oxalic Acid (Option B):** A corrosive organic acid that causes local mucosal damage and systemic hypocalcemia (leading to tetany) and renal failure due to calcium oxalate crystal deposition. * **Phenolic Acid / Carbolic Acid (Options C & D):** These are synonymous. Phenol poisoning is characterized by "Carboluria" (greenish-black urine), corrosive burns with a characteristic "whitish" appearance, and central nervous system depression. It does not cause acrodynia. **High-Yield Clinical Pearls for NEET-PG:** * **Mercury Triad:** Tremors (Danbury tremors/Glass-blower's shakes), Erithism (pathological shyness/irritability), and Gingivitis/Stomatitis. * **Minamata Disease:** Result of organic mercury (methylmercury) poisoning via contaminated fish. * **Hunter-Russell Syndrome:** Associated with organic mercury, presenting with ataxia, constricted visual fields, and dysarthria. * **Treatment:** BAL (British Anti-Lewisite) is the traditional chelator, though DMSA (Succimer) is now often preferred for chronic mercury poisoning.

Question 49: Chvostek/Weiss sign is seen in which poisoning?

A. Oxalic acid poisoning (Correct Answer)
B. Carbolic acid poisoning
C. Boric acid poisoning
D. Formic acid poisoning

Explanation: **Explanation:** **Chvostek sign** (also known as Weiss sign) is a clinical indicator of **hypocalcemia**. It is elicited by tapping the facial nerve at the angle of the jaw, resulting in twitching of the facial muscles. **Why Oxalic Acid is the correct answer:** Oxalic acid poisoning causes systemic toxicity primarily through its high affinity for calcium ions. Once absorbed, it reacts with serum calcium to form **insoluble calcium oxalate crystals**. This rapid depletion of ionized calcium leads to **acute hypocalcemia**. Clinical manifestations include tetany, muscle spasms, and positive Chvostek/Trousseau signs. Additionally, the precipitated calcium oxalate crystals can cause acute tubular necrosis and renal failure (Oxaluria). **Analysis of Incorrect Options:** * **Carbolic acid (Phenol):** Characterized by "Carboluria" (greenish-black urine), corrosive burns, and CNS depression. It does not specifically cause acute hypocalcemia. * **Boric acid:** Known for causing "boiled lobster syndrome" (intense erythroderma) and gastrointestinal distress, but not tetany. * **Formic acid:** Primarily associated with methanol metabolism; it causes severe metabolic acidosis and retinal toxicity, but not the specific neuromuscular irritability seen in oxalic acid poisoning. **High-Yield Clinical Pearls for NEET-PG:** * **Antidote for Oxalic Acid:** 10% Calcium Gluconate (to replenish calcium levels). * **Post-mortem finding:** "Coffee-ground" vomitus (due to altered blood) and calcium oxalate crystals in the kidneys. * **Ink-remover:** Oxalic acid is commonly used as a bleaching agent or ink-stain remover. * **Trousseau Sign:** Another sign of hypocalcemia (carpopedal spasm induced by inflating a BP cuff).

Question 50: Putrefaction is delayed in poisoning due to:

A. Carbolic acid (Correct Answer)
B. Organophosphorus
C. Lead
D. All

Explanation: **Explanation:** The process of putrefaction is primarily driven by bacterial action (especially *Clostridium welchii*) and autolysis. Any substance that acts as a potent antiseptic or preservative will inhibit bacterial growth, thereby delaying the decomposition of the body. **1. Why Carbolic Acid is Correct:** Carbolic acid (Phenol) is a powerful **antiseptic and disinfectant**. It denatures bacterial proteins and disrupts cell membranes. When ingested in lethal doses, it permeates the tissues and acts as a preservative, significantly slowing down the onset and progression of putrefaction. Other substances that similarly delay putrefaction include Arsenic, Antimony, Zinc Chloride, and heavy metals like Mercury. **2. Why the other options are incorrect:** * **Organophosphorus (OPC):** These compounds do not possess significant antiseptic properties. In fact, deaths due to OPC often involve respiratory failure and pulmonary edema; the increased moisture in the lungs can sometimes accelerate decomposition. * **Lead:** While heavy metals generally delay putrefaction, Lead is not classically associated with significant preservation of the body in the same clinical or forensic capacity as Phenol or Arsenic. **High-Yield Clinical Pearls for NEET-PG:** * **Delayed Putrefaction:** Seen in poisoning with Arsenic, Antimony, Phenol (Carbolic acid), Mercury, Zinc Chloride, and Nux Vomica (Strychnine). * **Accelerated Putrefaction:** Seen in deaths due to Septicemia, Gas gangrene, Hanging (in humid conditions), and poisoning by Hydrogen Sulphide. * **Carbolic Acid Sign:** Characterized by "Ochronosis" (pigmentation of cartilage) and "Carboluria" (urine turns green/black on standing). * **Mummification:** A modification of putrefaction seen in dry, warm climates, which also preserves the body.

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General Principles of Toxicology

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Corrosive Poisons

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Metallic Poisons

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Non-Metallic Poisons

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Organic Irritant Poisons

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Neurotic Poisons

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Cardiac Poisons

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Asphyxiant Poisons

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Food Poisoning

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Drug Abuse and Dependence

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Analytical Toxicology Methods

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Interpretation of Toxicology Results

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