SN3 SHORT NOTE 5M ★ High-yield

Describe strychnine poisoning and distinguish it from tetanus.

Forensic Medicine · 2nd Professional — Para-Clinical

Source and Mechanism

Strychnine is an alkaloid of the seeds of Strychnos nux-vomica (kuchila), a tree common in India, whose seeds are flat, disc-shaped, ash-grey and covered with fine silky hairs. It is used as a rodenticide and to poison stray dogs, is present in some traditional preparations, and is used as an adulterant of illicit drugs
Mechanism — strychnine is a competitive antagonist at glycine receptors in the spinal cord and brainstem. Glycine is the principal inhibitory transmitter of the cord, restraining the renshaw cells and the reflex arcs. Its blockade removes all inhibition, so that any sensory stimulus produces a massive, generalised, uncontrolled motor response
Crucially, this is a spinal action and not a cerebral one, which is why consciousness IS fully retained throughout — the patient is awake, aware, and in agony during every spasm. Fatal dose about 15 to 30 mg; fatal period 1 to 2 hours

Feature	Description
Onset	15 to 30 minutes; a bitter taste, restlessness, anxiety, twitching and stiffness of the face and neck
The convulsions	Sudden, violent, generalised tonic spasms lasting 1 to 2 minutes, recurring every 10 to 15 minutes and becoming more frequent
Opisthotonos	The body arched backwards on the heels and the head, from the extensor muscles overpowering the flexors — the classical posture
Risus sardonicus	A fixed grinning expression from spasm of the facial muscles, with retracted lips and raised eyebrows
Triggering	Each spasm is precipitated by the slightest stimulus — light, noise, a touch, a draught, even the approach of a person. This is diagnostic, and it dictates the entire management
Between the spasms	Complete relaxation, with exhaustion and profuse sweating; and the patient is fully conscious and terrified
Death	From asphyxia during a spasm, from exhaustion, or from rhabdomyolysis with hyperkalaemia and renal failure and hyperthermia
Postmortem	Rigor mortis appears early and is marked, and the opisthotonic posture may persist; no other characteristic finding, and the diagnosis rests on analysis of the viscera

CLINICAL PEARL

The patient is fully conscious throughout, which makes strychnine one of the cruellest of poisons and dictates the management. The action is spinal, not cerebral, so awareness is untouched. Everything follows from that and from the fact that every stimulus triggers a spasm: a dark, silent room, minimal handling, and sedation before anything else — routine nursing observations can themselves provoke a fatal convulsion.

Differential Diagnosis and Treatment

Feature	Strychnine	Tetanus
Onset	Minutes after ingestion	Days after a wound, with an incubation period
First muscles affected	The whole body almost at once; the face and neck early	Trismus (lockjaw) first, then descending
Between the spasms	Complete relaxation — the crucial distinction	Rigidity persists between spasms
Consciousness	Retained	Retained
A wound	Absent	Usually present, though it may be trivial or healed
Course	Resolves within hours if survived	Persists for weeks

Also distinguish from epilepsy (consciousness lost, no triggering by stimuli, post-ictal state), hypocalcaemic tetany (carpopedal spasm, Trousseau and Chvostek signs), meningitis, and dystonic reactions to phenothiazines and metoclopramide
Treatment — there is no antidote. Place the patient in a dark, quiet room and handle as little as possible; diazepam or another benzodiazepine in large doses is the first-line measure and should be given before anything else, including lavage; neuromuscular blockade with intubation and ventilation in severe cases, which is definitive; gastric lavage and activated charcoal only after the patient is sedated or paralysed, since passing a tube will otherwise provoke a convulsion; and active cooling, fluids and alkalinisation for rhabdomyolysis

Applied Aspects

Sedate before you examine or lavage; passing a nasogastric tube into an unsedated strychnine patient may kill them, and this inversion of the usual order is the key management point
Nurse in darkness and silence, and cluster all necessary handling; every touch, light and sound is a trigger
Distinguish from tetanus by the interval between spasms; complete relaxation means strychnine and persistent rigidity means tetanus
Treat the rhabdomyolysis; hyperkalaemia and renal failure kill patients who survive the convulsions, and hyperthermia must be managed actively
Consider it as an adulterant in a drug user with convulsions and full consciousness; strychnine has been used to cut illicit powders
Preserve viscera; there is nothing characteristic at autopsy beyond early marked rigor, and the diagnosis is chemical
Recovery is complete if the patient survives, which justifies aggressive ventilatory support however unwell they appear

All questions in Toxicology II — Specific Poisons

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