Forensic Toxicology — MCQs

Forensic Toxicology Indian Medical PG Practice Questions and MCQs

Question 841: Pica is associated with poisoning:

A. Arsenic
B. Phosphorus
C. Lead (Correct Answer)
D. Mercury

Explanation: ***Lead*** - **Pica**, the craving and consumption of non-food items, is a common symptom of **lead poisoning**, especially in children. - This behavior can lead to further ingestion of lead-containing substances, creating a vicious cycle of exposure. *Arsenic* - **Arsenic poisoning** primarily affects the skin, nervous system, and gastrointestinal tract, causing symptoms like **skin lesions**, neuropathy, and diarrhea. - While various neurological symptoms can occur, **pica** is not a characteristic feature of chronic arsenic exposure. *Phosphorus* - **Phosphorus poisoning** is typically associated with gastrointestinal irritation, liver damage, and cardiovascular effects, often from ingestion of pesticides or fireworks. - It does not commonly present with **pica** as a primary symptom. *Mercury* - **Mercury poisoning** manifests with neurological and psychiatric symptoms such as **tremors**, memory loss, and personality changes (**erethism**). - Pica is not a typical manifestation, although central nervous system effects can cause a range of behavioral changes.

Question 842: Dilated pupil with coma is seen in which poisoning?

A. Opium
B. Mushroom
C. Dhatura (Correct Answer)
D. Pilocarpine

Explanation: ***Dhatura*** - **Dhatura poisoning** is characterized by an **anticholinergic toxidrome**, leading to symptoms like **dilated pupils (mydriasis)**, dry mouth, flushed skin, tachycardia, and altered mental status progressing to coma. - The dilated pupils are a direct result of the **muscarinic receptor blockade** in the eye, preventing parasympathetic innervation. *Opium* - **Opium poisoning** typically causes **pinpoint pupils (miosis)**, respiratory depression, and central nervous system depression leading to coma. - This effect is due to the **opioid agonists** stimulating mu-opioid receptors. *Mushroom* - Mushroom poisoning can present with various toxidromes depending on the species; however, some muscarine-containing species can cause **miosis** (pinpoint pupils), salivation, and bradycardia, while others may cause delirium or hepatic failure. - **Dilated pupils** are not a characteristic feature of the more common deadly mushroom poisonings that lead to coma. *Pilocarpine* - **Pilocarpine** is a **direct cholinergic agonist** that stimulates muscarinic receptors and typically causes **miosis (constricted pupils)**, increased secretions, and bradycardia. - It would not lead to dilated pupils or coma in the manner described.

Question 843: Black foot is seen in which poisoning?

A. Arsenic (Correct Answer)
B. Lead
C. Mercury
D. Phosphorus

Explanation: ***Arsenic*** - **Arsenic poisoning** is known to cause peripheral vascular disease, leading to **ischemia** and **gangrene** of the extremities, which can manifest as "black foot." - This condition results from the toxic effects of arsenic on blood vessels, impairing circulation. *Lead* - **Lead poisoning** can cause **neurological symptoms** (e.g., foot drop, wrist drop), **gastrointestinal issues** (e.g., abdominal pain, constipation), and **anemia**. - It does not typically cause **black foot** or gangrene as a direct consequence of its vascular effects. *Mercury* - **Mercury poisoning** primarily affects the **nervous system**, kidneys, and gastrointestinal tract. - Symptoms include **neurological disturbances** (e.g., tremors, mood changes) and **acrodynia** (pink disease) in children; it is not associated with "black foot." *Phosphorus* - **Phosphorus poisoning** (especially white phosphorus) can cause severe **gastrointestinal corrosive injury**, **liver damage**, and **cardiac toxicity**. - It does not typically lead to peripheral vascular compromise or the specific manifestation of "black foot."

Question 844: Fatal dose of organophosphate poisoning is:

A. 20-25 mg/kg
B. 1-2 mg/kg (Correct Answer)
C. 10-15 mg/kg
D. 30-35 mg/kg

Explanation: ***1-2 mg/kg*** - This is the **fatal dose** for highly toxic organophosphates such as **parathion, phorate, and methyl parathion**, which are commonly encountered in clinical practice and forensic cases. - These compounds cause severe **cholinergic crisis** with respiratory failure, bronchospasm, excessive secretions, and cardiovascular collapse. - This dose range is most commonly cited in **forensic medicine literature** as the lethal dose for organophosphate poisoning. *10-15 mg/kg* - This range may represent the **fatal dose for moderately toxic organophosphates** like malathion or certain formulations with lower toxicity. - While this can certainly be lethal for some organophosphates, it is **not the typical fatal dose** for the highly toxic compounds most commonly involved in poisoning cases. - The LD50 varies widely depending on the specific organophosphate compound. *20-25 mg/kg* - This dose would be **highly lethal** and represents a massive overdose even for moderately toxic organophosphates. - It is significantly higher than the generally accepted **fatal dose** for most clinically relevant organophosphate compounds. - While certainly fatal, it exceeds the minimum lethal dose. *30-35 mg/kg* - This is a **supra-lethal dose** that would result in immediate and catastrophic organophosphate poisoning with rapid death. - This range is considerably higher than the recognized **minimum fatal dose** for any organophosphate compound. - It represents extreme overdose far beyond what is required to cause death.

Question 845: Which is the most heat-stable poison for post-mortem detection?

A. Mercury
B. Arsenic (Correct Answer)
C. Lead
D. Antimony

Explanation: ***Arsenic*** - **Arsenic** is biologically stable and is not easily metabolized or degraded, making it highly persistent in tissues even after death. - Its presence can be reliably detected in various tissues like **hair, nails, and bone** long after organ decomposition, due to its ability to bind to sulfhydryl groups in proteins. *Mercury* - While generally stable, **mercury** can volatilize at high temperatures, which might affect its detection in certain post-mortem scenarios or sample preparation methods. - Additionally, different forms of mercury (e.g., organic vs. inorganic) have varying degrees of stability and tissue distribution. *Lead* - **Lead** is stable in biological tissues and can be detected post-mortem, especially in bone. - However, compared to arsenic, lead's distribution can be more variable, and its detection methods might differ in sensitivity to heat degradation of surrounding organic matrices. *Antimony* - **Antimony** can form various compounds, and its stability can be influenced by the chemical environment and temperature. - While detectable, it may not possess the same exceptional heat stability and tissue persistence for post-mortem analysis as arsenic.

Question 846: Which metabolite best indicates chronic alcohol abuse in decomposed bodies?

A. Ethyl glucuronide
B. Phosphatidylethanol (Correct Answer)
C. Carbohydrate-deficient transferrin
D. Ethyl sulfate

Explanation: ***Phosphatidylethanol*** - **Phosphatidylethanol (PEth)** is a direct ethanol metabolite found in cell membranes, particularly red blood cells, and is highly specific to alcohol consumption. - Its long half-life (up to 4 weeks or more, depending on the specific PEth homologue) and stability in various biological matrices, including those of **decomposed bodies**, make it an excellent retrospective marker for chronic alcohol abuse. *Ethyl glucuronide* - While **ethyl glucuronide (EtG)** is a direct ethanol metabolite and a good marker for recent alcohol consumption (up to 2-5 days), it is less stable than PEth. - In **decomposed bodies**, EtG levels can degrade more rapidly due to enzymatic activity and putrefaction, making it a less reliable indicator of chronic use over extended post-mortem intervals. *Carbohydrate-deficient transferrin* - **Carbohydrate-deficient transferrin (CDT)** is a biomarker for chronic heavy alcohol consumption, reflecting changes in transferrin glycosylation. - However, CDT is typically measured in **serum** or **plasma** and is less stable in **decomposed tissue** compared to PEth, making its reliability for forensic analysis in such cases limited. *Ethyl sulfate* - **Ethyl sulfate (EtS)** is another direct ethanol metabolite similar to EtG, indicating recent alcohol consumption (detectable up to 2-3 days). - Like EtG, EtS is less stable than PEth in **post-mortem samples**, especially in decomposed bodies, limiting its utility as a long-term marker for chronic alcohol abuse under these conditions.

Question 847: Best preservative for viscera in poisoning cases?

A. 10% formalin
B. Absolute alcohol
C. Rectified spirit (Correct Answer)
D. Saturated saline

Explanation: ***Rectified spirit*** - **Rectified spirit** (ethanol 95%) is the best preservative for viscera in poisoning cases because it effectively preserves tissues without interfering with most toxicological analyses. - It prevents decomposition and bacterial growth while allowing for the detection of a wide range of **poisons**, including organic compounds and some volatile substances. *10% formalin* - **10% formalin** is primarily used for **histopathological examination** to preserve tissue architecture. - However, it can interfere with certain toxicological analyses and chemically alter some poisons, making their detection difficult. *Absolute alcohol* - While a good preservative, **absolute alcohol** (100% ethanol) is hygroscopic and can cause significant tissue dehydration and hardening. - It is often more expensive and less readily available than rectified spirit, and offers no significant advantage over rectified spirit for routine toxicological preservation. *Saturated saline* - **Saturated saline** is a poor choice for long-term preservation of viscera in poisoning cases. - It is not effective at preventing putrefaction and bacterial contamination, and it can dilute or leach out certain toxins from the tissues.

Question 848: Which poison shows cherry red discoloration of blood but normal PaO2 on blood gas analysis?

A. Cyanide
B. Hydrogen sulfide
C. Carbon monoxide (Correct Answer)
D. Nitrites

Explanation: ***Carbon monoxide*** - **Carbon monoxide (CO)** binds to **hemoglobin** with a much higher affinity than oxygen, forming **carboxyhemoglobin**. This complex is bright red, causing the characteristic **cherry-red discoloration of blood** and skin. - Despite the impaired oxygen delivery, the partial pressure of dissolved oxygen in the blood (**PaO2**) remains normal because CO poisoning affects oxygen binding to hemoglobin rather than the amount of oxygen dissolved in plasma. *Cyanide* - **Cyanide** inhibits **cytochrome c oxidase**, impairing cellular oxygen utilization and leading to **lactic acidosis** and cellular hypoxia. - While it can cause cellular hypoxia, it does not typically produce cherry-red discoloration and usually results in an **arteriovenous oxygen difference** that is small as tissues cannot extract oxygen from the blood effectively. *Hydrogen sulfide* - **Hydrogen sulfide (H2S)** also inhibits **cytochrome c oxidase**, leading to cellular hypoxia similar to cyanide. - Although it can cause a "rotten egg" smell and rapid collapse, it does not typically produce the characteristic **cherry-red discoloration** of blood. *Nitrites* - **Nitrites** (and other oxidizing agents) cause **methemoglobinemia**, where the iron in hemoglobin is oxidized from the ferrous (Fe2+) to the ferric (Fe3+) state, which cannot bind oxygen. - This condition causes the blood to appear **chocolate brown** or **bluish-gray**, not cherry-red, and can lead to a **functional anemia** despite normal PaO2.

Question 849: A 40-year-old female consumed a white-colored pesticide powder and presents with a potassium level of 2.5 mEq/L. O/E she has an irregular pulse and muscle paralysis. ECG shows multiple ventricular ectopics. What is the suspected poison?

A. Barium carbonate (Correct Answer)
B. Zinc phosphide
C. Aluminum phosphide
D. Warfarin toxicity

Explanation: ***Barium carbonate*** - **Barium carbonate** is a common rodenticide often found as a white powder, which, when ingested, specifically blocks potassium channels, leading to severe **hypokalemia**, **muscle paralysis**, and cardiac arrhythmias such as ventricular ectopics and an irregular pulse. - The clinical presentation of profound hypokalemia (2.5 mEq/L) causing muscle and cardiac effects after ingesting a white pesticide powder is highly characteristic of barium poisoning. *Zinc phosphide* - **Zinc phosphide** poisoning typically presents with severe gastrointestinal symptoms, metabolic acidosis, and profound circulatory collapse, often accompanied by a garlic or fishy odor on the breath. - While it is a pesticide, it does not primarily cause severe hypokalemia, muscle paralysis, or ventricular ectopics as its hallmark features. *Aluminum phosphide* - **Aluminum phosphide** poisoning causes severe metabolic acidosis, shock, refractory hypotension, and cardiac arrhythmias, often with a garlic-like odor. - It rapidly releases phosphine gas upon contact with gastric acid, leading to multi-organ failure rather than the predominant hypokalemia, muscle paralysis, and ventricular ectopics seen here. *Warfarin toxicity* - **Warfarin toxicity** is characterized by bleeding disorders due to its anticoagulant effects, leading to an elevated INR and various hemorrhagic manifestations. - It does not cause acute hypokalemia, muscle paralysis, or cardiac arrhythmias as described in this patient, and it is usually a blood thinner, not typically a white pesticide powder.

Question 850: Which of the following poisons causes cherry-red discoloration of the skin?

A. Cyanide
B. Arsenic
C. Lead
D. Carbon monoxide (Correct Answer)

Explanation: ***Carbon monoxide*** - **Carbon monoxide** binds to hemoglobin with high affinity, forming **carboxyhemoglobin**, which is bright red. - This high level of **carboxyhemoglobin** in the capillaries causes the characteristic **cherry-red discoloration** of the skin and mucous membranes. *Cyanide* - **Cyanide** inhibits cytochrome c oxidase, leading to **cellular hypoxia** despite adequate oxygen delivery. - While it interferes with oxygen utilization, it does not typically cause **cherry-red skin**; rather, skin color can be variable, sometimes appearing normal or even cyanotic in severe cases. *Arsenic* - **Arsenic poisoning** primarily affects multiple organ systems and can cause gastrointestinal symptoms, neurological damage, and skin lesions (e.g., hyperpigmentation, keratosis). - It does not cause a **cherry-red discoloration** of the skin. *Lead* - **Lead poisoning** is associated with neurological, gastrointestinal, and hematological symptoms, including **anemia** and **peripheral neuropathy**. - It can cause a **pale or grayish skin tone** due to anemia, but not a **cherry-red discoloration**.

Practice by Chapter

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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