Describe the diagnosis of poisoning in the living and in the dead.

Diagnosis in the Living

• Suspect poisoning in: a sudden illness in a previously healthy person, particularly with a rapid onset shortly after food, drink or medication; similar symptoms in several people who ate together, which points to food or to deliberate mass poisoning; an illness that does not fit any recognised disease pattern; unexplained coma, convulsions, arrhythmia or metabolic acidosis; and a recurrent illness that improves in hospital and returns at home, which is the classic pattern of chronic homicidal poisoning
• The history is the most valuable single element — and must be obtained from relatives, friends, the police and the scene as well as from the patient, who may be unconscious, confused or deliberately misleading. Ask what was available in the house, what the occupation is (a farmer has pesticides), and what medicines are in the home
• The container, tablets, syringe or plant material brought with the patient is often the diagnosis, and must be preserved rather than discarded

• The pupils are the single most useful sign at the bedside, and they divide the unconscious poisoned patient into two groups.
• pinpoint pupils with depressed respiration mean opioid until proved otherwise — and naloxone is both diagnosis and treatment.
• Pinpoint with profuse secretions, fasciculation and bradycardia means organophosphate. Wide pupils with a dry, hot, flushed patient mean anticholinergic, and in India that means datura.

Diagnosis in the Dead

• Circumstantial evidence — the scene, containers, tablets, blister packs, syringes, a suicide note, the smell in the room, vomit, the occupation, and the history of illness and of psychiatric disorder. The scene is frequently more informative than the body
• External examination — the colour of the lividity; staining, corrosion and burns around the mouth, chin and neck from a corrosive; the smell; needle marks; jaundice; the state of the clothing; and vomit on the face and clothing
• Internal examination — smell the stomach on opening it, cautiously; the state of the gastric mucosa, which may be congested, eroded, ulcerated, blackened, softened or perforated; the contents, including tablet fragments, plant material and coloured residue; and the changes in the liver, kidneys and lungs
• The findings are often non-specific or entirely absent, particularly in poisoning by alkaloids, opioids and many drugs. A negative autopsy is entirely compatible with fatal poisoning, which is why viscera must be preserved in every unexplained death
• Chemical analysis of the viscera is the only conclusive evidence, and everything else is suggestive. The autopsy findings, the circumstances and the analysis are read together
• Supporting investigations — histopathology of the liver, kidney, heart and brain; and specific tests such as carboxyhaemoglobin, cholinesterase and methaemoglobin estimation, which must be requested specifically

Applied Aspects

• Look at the pupils and the secretions first in any unconscious patient; they identify the two commonest treatable poisonings in India within seconds
• Preserve the container and the first gastric aspirate; the aspirate is the single most valuable specimen and is routinely discarded down a sink
• Send the scene material with the patient, and ask the police to preserve what remains; the diagnosis is often written on the packet
• Do not exclude cyanide because you cannot smell it; the ability is genetically determined and a large minority of people simply cannot
• Suspect chronic poisoning where an illness recurs at home and remits in hospital; this pattern, with gastrointestinal symptoms and neuropathy, is the classical presentation of arsenic and of thallium
• Take viscera in every sudden, unexplained or suspicious death, whatever the autopsy shows; a negative examination is entirely consistent with poisoning and the material cannot be recovered once the body is released
• Dry, hot, flushed and delirious means anticholinergic, and in India that means datura until proved otherwise
• Wet, bradycardic and fasciculating means organophosphate, and the pupils are pinpoint in both this and opioid poisoning
• Chocolate-brown lividity means methaemoglobin — nitrites, chlorates, aniline or dapsone — and methylene blue is the antidote
• Garlic odour covers phosphorus, arsenic and organophosphates, and aluminium phosphide, which is much the commonest of them in India
• Ask the occupation; a farmer has pesticides, a jeweller has cyanide, and a painter has lead, and the answer often makes the diagnosis
• An illness that remits in hospital and returns at home is the classical pattern of chronic homicidal poisoning and should never be ignored
• Request the specific tests — carboxyhaemoglobin, cholinesterase and methaemoglobin are not part of any routine screen
• Histopathology supports the toxicology, and the liver, kidney, heart and brain should be sampled in every suspected poisoning death
• Several people ill after one meal means food or mass poisoning, and the shared meal is the first thing to establish
• A negative autopsy is fully compatible with fatal poisoning, which is why viscera are taken in every unexplained death
• Methanol is odourless, and the smell of alcohol on the breath may come entirely from a mixed drink
• Rain-drop pigmentation and Mees lines point to chronic arsenic, and a Burtonian line to chronic lead
• Look at the scene, not only the body; containers, blister packs, a note and the smell of the room are frequently the diagnosis
• The first gastric aspirate is the best specimen and is routinely poured down a sink before anyone thinks of preserving it
• Chemical analysis alone is conclusive; the autopsy findings and the circumstances are suggestive and are read together with it
• Postmortem redistribution raises cardiac drug levels, so femoral blood is preferred wherever it can be obtained
• Ask what medicines are in the house; the poison is usually something that was already there rather than something obtained
• Jaundice suggests paracetamol or phosphorus, and appears after a latent period during which the patient looks deceptively well
• Convulsions suggest strychnine, isoniazid or a tricyclic, and organophosphate poisoning where the cholinergic signs are also present