Forensic Toxicology Practice Questions

Q: In CO poisoning all of the following clinical features are seen, EXCEPT?

Cyanosis. **Explanation:** The correct answer is **Cyanosis**. Carbon Monoxide (CO) poisoning is a classic "trap" in forensic medicine because, despite the presence of cellular hypoxia, patients do **not** present with cyanosis. **1. Why Cyanosis is the correct answer (The Exception):** Cyanosis occurs when there is an absolute increase in deoxygenated hemoglobin (>5g/dL). In CO poisoning, CO binds to hemoglobin with an affinity 200–250 times greater than oxygen, forming **Carboxyhemoglobin (COHb)**. Carboxyhemoglobin has a distinctive **cherry-red color**. Therefore, the skin and mucous membranes appear bright red or pinkish rather than blue, even though the tissues are starving for oxygen. **2. Analysis of Incorrect Options:** * **Cerebral Edema:** CO causes direct neurotoxicity and hypoxia-induced vascular leakage, leading to increased intracranial pressure and cerebral edema. * **Convulsions:** Severe hypoxia and metabolic acidosis caused by CO poisoning frequently trigger seizures/convulsions as the brain's electrical activity is disrupted. * **Bradycardia:** While initial compensation may cause tachycardia, terminal stages of CO poisoning involve myocardial depression and hypoxia of the sinoatrial node, leading to bradycardia and eventual cardiac arrest. **Clinical Pearls for NEET-PG:** * **Cherry-red discoloration:** Best seen in post-mortem staining (lividity), muscles, and viscera. * **Mechanism:** CO causes a **Leftward shift** of the Oxygen-Dissociation Curve, preventing the release of oxygen to tissues. * **CT Scan finding:** Bilateral necrosis of the **Globus Pallidus** is a pathognomonic radiological sign of CO poisoning. * **Treatment:** 100% Hyperbaric Oxygen (HBO) to reduce the half-life of COHb.

Q: A patient presents with pink skin and mucosa, a breath odor described as bitter almond, and frothy discharge. What is the most likely cause of death?

Hydrogen cyanide (HCN) poisoning. ### Explanation The correct answer is **Hydrogen cyanide (HCN) poisoning**. **1. Why Hydrogen Cyanide (HCN) is correct:** The clinical triad of **bitter almond odor**, **pinkish/cherry-red discoloration** of the skin/mucosa, and **frothy discharge** from the mouth is pathognomonic for cyanide poisoning. * **Mechanism:** Cyanide inhibits the enzyme **cytochrome oxidase $a_3$** in the electron transport chain. This prevents cells from utilizing oxygen (histotoxic hypoxia). * **Coloration:** Because tissues cannot take up oxygen, the venous blood remains highly oxygenated (oxyhemoglobin), leading to the characteristic bright pink or cherry-red appearance of the skin and post-mortem lividity. **2. Why other options are incorrect:** * **Carbon monoxide (CO):** While CO also causes cherry-red discoloration (due to carboxyhemoglobin), it lacks the bitter almond odor. * **Hydrogen sulfide ($H_2S$):** This causes a characteristic **rotten egg odor**. Post-mortem lividity is typically **bluish-green** due to the formation of sulfhemoglobin. * **Organophosphate (OPC):** While OPC poisoning presents with excessive frothing and miosis, the breath has a distinct **garlic-like odor**, not bitter almond. **3. High-Yield Clinical Pearls for NEET-PG:** * **Odor Mnemonics:** * Bitter Almonds $\rightarrow$ Cyanide * Garlic $\rightarrow$ OPC, Arsenic, Phosphorus * Rotten Eggs $\rightarrow$ $H_2S$ * Kerosene $\rightarrow$ Organochlorines * **Lividity Colors:** * Cherry Red $\rightarrow$ CO, Cyanide, Hypothermia * Chocolate Brown $\rightarrow$ Nitrates, Potassium Chlorate (Methemoglobinemia) * Blue-Green $\rightarrow$ $H_2S$ * **Antidote for Cyanide:** Hydroxocobalamin (preferred) or the Cyanide Antidote Kit (Amyl nitrite, Sodium nitrite, and Sodium thiosulfate).

Q: Chalky white deposits in teeth are seen with which acid?

Sulphuric acid. **Explanation:** Corrosive acids cause characteristic discoloration and damage to the oral mucosa and teeth based on their chemical interaction with tissues. **Why Sulphuric Acid is Correct:** Sulphuric acid is a powerful dehydrating agent. When ingested, it causes intense charring (carbonization) of tissues, leading to a blackish discoloration of the mouth and skin. However, its action on the **dental enamel** is distinct; it reacts with the calcium in the teeth to form calcium sulphate, which manifests as **chalky white deposits** or a dull, opaque white appearance of the teeth. **Analysis of Incorrect Options:** * **Carbolic Acid (Phenol):** Known as a "local anesthetic" corrosive. It causes the mucosa to become **greyish-white**, tough, and leathery (fixation of proteins), but does not produce chalky white dental deposits. * **Oxalic Acid:** While it can cause white patches on the mucous membranes due to its corrosive nature, it is primarily known for causing hypocalcemia and renal failure (oxalate crystals). It is not the classic cause of chalky teeth. * **Nitric Acid:** This acid reacts with the proteins in the tissue to produce picric acid (Xanthoproteic reaction), resulting in a characteristic **yellowish discoloration** of the skin, mucosa, and teeth. **High-Yield Clinical Pearls for NEET-PG:** * **Sulphuric Acid:** Known as "Oil of Vitriol." Causes "Vitriolage" (throwing acid with intent to disfigure). * **Nitric Acid:** Known as "Aqua Fortis." Causes yellow staining. * **Hydrochloric Acid:** Known as "Spirit of Salt." Causes greyish-white staining (less intense than others). * **Stomach Appearance:** Sulphuric acid typically causes a "perforated, charred, and black" (coffee-ground) appearance of the stomach.

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

Arsenic poisoning. **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).

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

Phenol. 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.

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

Potassium cyanide poisoning. **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.

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

Organophosphorous poisoning. **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).

Q: 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?

Strychnine. ### 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).

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

None of the above. **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 1

In CO poisoning all of the following clinical features are seen, EXCEPT?

Accepted Answer

Cyanosis

Answer

Cerebral edema

Answer

Convulsions

Answer

Bradycardia

Question 2

A patient presents with pink skin and mucosa, a breath odor described as bitter almond, and frothy discharge. What is the most likely cause of death?

Accepted Answer

Hydrogen cyanide (HCN) poisoning

Answer

Hydrogen sulfide (H2S) poisoning

Answer

Carbon monoxide (CO) poisoning

Answer

Organophosphate (OPC) poisoning

Question 3

Chalky white deposits in teeth are seen with which acid?

Accepted Answer

Sulphuric acid

Answer

Carbolic acid

Answer

Oxalic acid

Answer

Nitric acid

Question 4

In which of the following poisonings is emesis not contraindicated?

Accepted Answer

Arsenic poisoning

Answer

Kerosene poisoning

Answer

Nux vomica poisoning

Answer

Oxalic acid poisoning

Question 5

What type of breathing is observed in barbiturate poisoning?

Accepted Answer

Rapid and shallow

Answer

Rapid and deep

Answer

Slow and shallow

Answer

Normal breathing

Question 6

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

Accepted Answer

Phenol

Answer

Cyanide

Answer

Insecticides

Answer

Alphos

Question 7

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

Accepted Answer

Potassium cyanide poisoning

Answer

Opium poisoning

Answer

Hydrogen sulfide poisoning

Answer

Cyanide poisoning

Question 8

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

Accepted Answer

Organophosphorous poisoning

Answer

Opium poisoning

Answer

Acute alcohol intoxication

Answer

Pontine hemorrhage

Question 9

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?

Accepted Answer

Strychnine

Answer

Atropine

Answer

Ricin

Answer

Bhilawanol

Question 10

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

Accepted Answer

None of the above

Answer

Nausea

Answer

Headache

Answer

Muscular weakness

Forensic Toxicology — MCQs

Forensic Toxicology — MCQs

On this page

Practice by Chapter

Want unlimited practice?