ACMT Toxicology Visual Pearls: Awake Seizures?

By Kregg Laundon, MD September 14, 2020 0 comments

Which of the following rodenticides, often used to kill the rodent pictured, causes seizure-like activity without altered mental status or a postictal period?

Barium
Brodifacoum
Carbamate
Strychnine
Zinc phosphide

Reveal the Answer

Answer: 4 – Strychnine in rodenticide, often used in “gopher bait.”

What is strychnine and how does it cause toxicity [1-5]?

Strychnine is an odorless, bitter-tasting alkaloid derived from the seeds of the Strychnos nux-vomica and related plants.
Strychnine is still commercially available as a rodenticide in the US, but use is banned elsewhere.
Strychnine is a competitive antagonist of the inhibitory neurotransmitter glycine with predominant activity in the spinal cord.
Exposed patients develop painful involuntary muscle contractions which can be mistaken for seizure activity.
Mental status remains intact

How are patients exposed [5,6]?

Accidental or intentional ingestion of rodenticides containing strychnine
Use of the Chinese or Cambodian herbal medications Ma Qian Zi and slang nut
Historically, use of cocaine or heroin adulterated with strychnine
Inhalation or dermal exposure also results in toxicity

How does strychnine toxicity present [5-9]?

Onset is rapid after oral exposure but may be delayed up to 12 hours following dermal exposure
Episodic, painful, involuntary muscle spasms lasting up to 2 minutes at a time that recur over a 12-24 hour period
Flexion of upper extremities and extension of lower extremities are commonly reported
Spasms can be triggered by mild stimuli such as turning on room lights
Patients are reported to be hyperexcitable or agitated
Nystagmus, clonus, risus sardonicus, opisthotonos, and trismus are also reported
Prolonged muscle contraction can result in rhabdomyolysis and acute kidney injury, metabolic acidosis, hypocalcemia, hyperkalemia, and hyperthermia.
Compartment syndrome has been reported
Hypoxia may occur due to hypoventilation
True seizures and death due to respiratory and/or cardiac arrest have been reported

How do you diagnose and treat strychnine toxicity [2,5,8-10]?

History and physical exam
Decontaminate skin for dermal exposure
Acute tetanus should be part of the differential diagnosis with other considerations including status epilepticus, dystonic reaction, and NMS
Activated charcoal may be considered if less than 1-2 hours post-ingestion and airway is protected
Diagnostic testing should include a chemistry panel, renal function, and CPK
Limit noise and physical stimulation by placing the patient in a quiet dark room
Strychnine levels may be obtained from blood or urine.
Supportive care includes the administration of IV fluids and the correction of electrolyte abnormalities.
Treatment with benzodiazepines will increase inhibitory neurotransmission and promote muscle relaxation.
If intubation is required, avoid nondepolarizing neuromuscular blockers and sedate generously.
In extreme cases, paralytics may be required.
Monitor for hyperthermia and treat if necessary

Take-Home Bedside Pearls:

Consider strychnine toxicity in patients with apparent awake “seizures.”
Aggressive use of benzodiazepines is the mainstay of therapy.
Keep the patient in a low stimulation setting.
Intubation with nondepolarizing paralytics and active cooling may be needed.
Evaluate for rhabdomyolysis, acute kidney injury, and electrolyte abnormalities.

Want more ACMT Visual Pearls? Check out the ALiEM Archives!

This post has been peer-reviewed on behalf of ACMT by Dr Bryan Judge, Dr Louise Kao, and Dr David Wood.

References

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Mackerer CR, Kochman RL, Shen TF, Hershenson FM. The binding of strychnine and strychnine analogs to synaptic membranes of rat brainstem and spinal cord. J Pharmacol Exp Ther. 1977;201(2):326-331. PMID: 16120
Curtis DR, Duggan AW, Johnston GA. The specificity of strychnine as a glycine antagonist in the mammalian spinal cord. Exp Brain Res. 1971;12(5):547-565. doi:10.1007/BF00234248. PMID: 5093729
Teitelbaum DT, Ott JE. Acute strychnine intoxication. Clin Toxicol. 1970;3(2):267-273. doi:10.3109/15563657008990475. PMID: 5527848
Chan Y. Strychnine. In: Hoffman RS, Howland M, Lewin NA, Nelson LS, Goldfrank LR. eds. Goldfrank’s Toxicological Emergencies, 11e New York, NY: McGraw-Hill; 2019
Boyd RE, Brennan PT, Deng JF, Rochester DF, Spyker DA. Strychnine poisoning. Recovery from profound lactic acidosis, hyperthermia, and rhabdomyolysis. Am J Med. 1983;74(3):507-512. doi:10.1016/0002-9343(83)90999-3. PMID: 6829597
Hardin JA, Griggs RC. Diazepam treatment in a case of strychnine poisoning. Lancet. 1971;2(7720):372-373. doi:10.1016/s0140-6736(71)90085-7. PMID: 4105067
Jackson G, Ng SH, Diggle GE, Bourke IG. Strychnine poisoning treated successfully with diazepam. Br Med J. 1971;3(5773):519-520. doi:10.1136/bmj.3.5773.519. PMID: 341168
Maron BJ, Krupp JR, Tune B. Strychnine poisoning successfully treated with diazepam. J Pediatr. 1971;78(4):697-699. doi:10.1016/s0022-3476(71)80480-8. PMID: 5547830