Neurotoxicology — the recognition and treatment of toxin-induced neurologic syndromes — encompasses a vast territory from common drug overdoses to environmental exposures, biological toxins, heavy metals, drug withdrawal syndromes, and medication-induced neurologic emergencies. The neurologist must recognize the toxidrome quickly to administer appropriate antidote, prevent progression, and support the patient through recovery. This page covers the major neurotoxicology emergencies and their pharmacologic management.

Toxidromes

Anticholinergic Toxidrome

• “Mad as a hatter, red as a beet, hot as a hare, dry as a bone, blind as a bat.”
• Confusion, hyperthermia, flushed skin, dry mucous membranes, mydriasis, urinary retention, decreased bowel sounds.
• Causes: TCAs, antihistamines (diphenhydramine), antipsychotics, atropine, scopolamine, jimson weed (Datura), some plants.
• Treatment: supportive; physostigmine (1-2 mg IV, repeat as needed) for severe cases with cardiac monitoring; avoid in TCA overdose (worsens cardiac).

Cholinergic Toxidrome

• SLUDGE: salivation, lacrimation, urination, defecation, GI cramps, emesis.
• Plus: miosis, bradycardia, bronchospasm, fasciculations.
• Causes: organophosphates (pesticides, nerve agents), carbamates, pyridostigmine overdose.
• Treatment: atropine large doses; pralidoxime for organophosphates (NOT carbamates).

Sympathomimetic Toxidrome

• Tachycardia, hypertension, mydriasis, agitation, hyperthermia, diaphoresis.
• Causes: cocaine, amphetamines, methamphetamine, MDMA, cathinones (“bath salts”).
• Treatment: benzodiazepines first-line; vasodilators for HTN; aggressive cooling.
• Avoid pure β-blockers (unopposed α).

Sedative-Hypnotic Toxidrome

• Sedation, hypotension, bradypnea, hypothermia.
• Causes: benzodiazepines, barbiturates, alcohol, opioids.
• Treatment: supportive; specific antidotes for some.

Opioid Toxidrome

• Pinpoint pupils, respiratory depression, sedation.
• Treatment: naloxone (Narcan).

Serotonin Syndrome

• Mental status changes + autonomic hyperactivity + neuromuscular abnormalities (hyperreflexia, clonus, rigidity).
• Causes: combination of serotonergic agents.
• Treatment: discontinue serotonergic drugs; cyproheptadine; benzodiazepines; aggressive cooling.

Specific Antidotes

Heavy Metal Poisoning

Lead

• Clinical: encephalopathy, peripheral neuropathy (wrist/foot drop), abdominal pain, anemia.
• BLL >70 (severe): IM dimercaprol + IV EDTA.
• BLL 45-69: oral succimer.
• Encephalopathy: emergent chelation.
• Children: lower threshold for chelation.
• Source identification critical.

Mercury

• Elemental, inorganic, organic forms differ.
• Organic (methylmercury): neurologic syndrome with cerebellar, sensory; Minamata disease.
• Treatment: dimercaprol for inorganic; chelation less effective for organic.

Arsenic

• Encephalopathy, peripheral neuropathy, skin changes, Mees lines.
• Treatment: dimercaprol or succimer.

Manganese

• Parkinsonism (atypical with dystonia).
• Welding, mining exposures.
• Treatment: limited; chelation modest benefit; remove from exposure.

Thallium

• Painful peripheral neuropathy + alopecia + GI.
• Treatment: Prussian blue (oral).

Carbon Monoxide

• Headache, confusion, syncope, neurologic deficits.
• Cherry red appearance (often absent).
• Delayed neurologic sequelae weeks later.
• Treatment: 100% O2; hyperbaric O2 for severe (COHb >25%, neurologic symptoms, cardiac symptoms, pregnancy).

Methanol / Ethylene Glycol

• Methanol: visual loss (toxic to optic nerve).
• Ethylene glycol: renal failure, calcium oxalate crystals.
• Both: high anion gap metabolic acidosis.
• Treatment: fomepizole (preferred) or ethanol (competes for ADH); hemodialysis; bicarbonate; folate (methanol); thiamine + pyridoxine (ethylene glycol).

Alcohol-Related Neurologic Syndromes

Wernicke Encephalopathy

• Triad: ataxia + ophthalmoplegia + confusion.
• Thiamine deficiency.
• IV thiamine 500 mg TID × 3 days, then 250 mg daily.
• GIVE THIAMINE BEFORE GLUCOSE in deficient patient.
• Korsakoff: late, often irreversible; antegrade amnesia.

Alcohol Withdrawal

• Tremulousness, hyperreflexia, hallucinations, autonomic hyperactivity, seizures, delirium tremens.
• Benzodiazepines: lorazepam, diazepam, chlordiazepoxide; symptom-triggered dosing (CIWA).
• Phenobarbital alternative.
• Thiamine, multivitamin, IV fluids.
• Seizures: benzodiazepines.
• DT: ICU; high-dose benzodiazepines; supportive.

Alcoholic Cerebellar Degeneration

• Abstinence; thiamine; supportive.

Marchiafava-Bignami

• Corpus callosum demyelination.
• Thiamine, B-complex.

Central Pontine Myelinolysis

• Rapid Na⁺ correction in chronic hyponatremia.
• Prevention: limit Na⁺ correction to 8-12 mEq/L/24 hours; less in chronic hyponatremia.
• Treatment: supportive; some success with relowering Na⁺.

Benzodiazepine and Opioid Overdose

Benzodiazepine

• Respiratory depression less severe than opioids unless combined.
• Flumazenil: rapid reversal; AVOID in chronic users (precipitates withdrawal seizures); use cautiously.
• Supportive care.

Opioid

• Respiratory depression, pinpoint pupils.
• Naloxone 0.4-2 mg IV/IM/intranasal; titrate to respiratory rate.
• Continuous infusion for long-acting opioids.
• Repeat doses needed for methadone, fentanyl patches.
• Nalmefene: long-acting alternative (Opvee 2023).

Lithium Toxicity

• Tremor, ataxia, dysarthria, confusion, seizure.
• Range concerns: levels >1.5 mEq/L acute; can have toxicity at “therapeutic” levels in chronic users.
• Treatment: dialysis for severe (Li >4.0 acute; >2.5 with symptoms; chronic with neurologic findings).
• Supportive; cautious fluid replacement.

Acetaminophen Overdose

• Hepatic toxicity primary; can cause encephalopathy in fulminant failure.
• N-acetylcysteine (NAC): oral or IV.
• Rumack-Matthew nomogram for treatment decision.
• Liver transplant for fulminant failure.

TCA Overdose

• QRS widening (sodium channel block), seizures, anticholinergic.
• Treatment: sodium bicarbonate IV for QRS widening; benzodiazepines for seizures; supportive.
• Lipid emulsion therapy: emerging for refractory cardiotoxicity.

Cyanide Poisoning

• Smoke inhalation, industrial exposure, suicide attempts.
• High anion gap acidosis, severe lactic acidosis, cherry-red skin.
• Treatment: hydroxocobalamin (5 g IV; preferred); amyl nitrite + sodium nitrite + sodium thiosulfate (alternative).

Methemoglobinemia

• Causes: dapsone, benzocaine, nitrates, nitrites.
• Cyanosis with normal PaO2.
• Treatment: methylene blue 1-2 mg/kg IV.
• Avoid methylene blue + serotonergic drugs (serotonin syndrome).

Mushroom Poisoning

• Cyclopeptide-containing (Amanita): hepatotoxic; supportive; N-acetylcysteine; silibinin.
• Muscimol (Amanita muscaria): GABA effects; supportive.
• Psilocybin: serotonergic; benzos for agitation; supportive.

Black Widow Spider

• Severe muscle cramping, autonomic hyperactivity.
• Treatment: opioids, benzodiazepines, calcium gluconate; antivenom for severe.

Drug-Induced Neurologic Syndromes

• NMS: discontinue antipsychotic; dantrolene; bromocriptine.
• Serotonin syndrome: discontinue; cyproheptadine; benzos.
• Drug-induced parkinsonism: discontinue offending drug; benztropine.
• Acute dystonic reaction: benadryl 50 mg IV; benztropine.
• Akathisia: β-blockers, benzodiazepines.
• Tardive dyskinesia: VMAT2 inhibitors.
• Hypothermic injury: rewarm.
• Hyperthermic injury: cool aggressively.

Specific Considerations

Pregnancy

• Most toxicology principles same.
• Some antidotes have specific considerations (e.g., chelation in pregnancy weighed carefully).
• Hyperbaric O2 in CO pregnancy: lower threshold.

Pediatrics

• Different toxicology spectrum.
• Lower thresholds for chelation in lead.
• Iron toxicity: deferoxamine.

Geriatric

• Polypharmacy increases toxicology risk.
• Anticholinergic burden cumulative.
• Falls and trauma complications.

🔍 Did You Know?

The advent of hydroxocobalamin (Cyanokit) as the primary antidote for cyanide poisoning has transformed the management of smoke inhalation victims — one of the most common cyanide exposure scenarios in modern medicine. Cyanide is released from burning plastics, foams, and synthetic materials, and is a major contributor to morbidity and mortality in fire victims (alongside CO and direct thermal injury). The traditional cyanide kit (amyl nitrite + sodium nitrite + sodium thiosulfate) had significant drawbacks: nitrites induce methemoglobinemia, problematic in patients with concurrent CO poisoning (compounded oxygen-carrying impairment). Hydroxocobalamin binds cyanide to form cyanocobalamin (vitamin B12), which is renally excreted, providing rapid neutralization without methemoglobinemia. The clinical implications are profound: any smoke inhalation victim with neurologic depression, hemodynamic instability, or significant lactic acidosis should receive empiric hydroxocobalamin 5 g IV — without waiting for cyanide level confirmation. The drug is safe even when cyanide is absent (the cobalamin is simply excreted). For practicing neurologists and emergency physicians, the take-home: fire victims with neurologic compromise need 100% O2 PLUS empiric hydroxocobalamin; the combination addresses both CO and cyanide. The lesson generalizes: empiric treatment of likely toxidromes can be life-saving when confirmation takes time, particularly with safe antidotes that can be given before laboratory confirmation. For practicing neurologists, knowing the major toxidromes and their treatments is essential — the difference between recovery and death often depends on rapid recognition and treatment.

Pitfalls and Pearls

• Anticholinergic: confusion + hyperthermia + dry; physostigmine for severe.
• Cholinergic: SLUDGE; atropine + pralidoxime (OP only).
• Sympathomimetic: benzos first-line; avoid pure β-blockers.
• Serotonin syndrome: cyproheptadine + benzos + discontinuation + cooling.
• NMS: discontinue D2 antagonist + dantrolene + bromocriptine.
• Acetaminophen overdose: N-acetylcysteine.
• Methanol/ethylene glycol: fomepizole + dialysis.
• Cyanide: hydroxocobalamin (empirical for smoke inhalation).
• CO: 100% O2; hyperbaric for severe/pregnant.
• Methemoglobinemia: methylene blue (avoid with serotonergics).
• Wernicke: thiamine BEFORE glucose.
• Lead encephalopathy: emergent chelation (BAL + EDTA).
• TCA overdose: NaHCO3 for QRS widening.
• Lithium toxicity: dialysis for severe.
• Opioid overdose: naloxone; titrate to respiratory rate.
• Benzo overdose: flumazenil cautiously (withdrawal in chronic users).
• Reverse anticoagulants: idarucizumab (dabigatran), andexanet (Xa inhibitors), 4-factor PCC + vitamin K (warfarin).
• Central pontine myelinolysis: prevent by slow Na⁺ correction.
• Alcohol withdrawal: benzodiazepines; thiamine.

References

1. Olson KR, ed. Poisoning & Drug Overdose. 7th ed. McGraw-Hill; 2018.
2. Walter FG, Klein R, Thomas RG, et al. Antidotes for poisoning. Crit Care Clin. 2017;33(4):725-744.
3. Bird SB, Sutherland TJ, Gresham C, et al. OP-IDN: poisoning by organophosphorus compounds. Clin Toxicol (Phila). 2008;46(4):341-345.
4. Henry JA, Hill IR. Fatal interaction between ritonavir and MDMA. Lancet. 1998;352(9142):1751-1752.
5. Watson WA, Litovitz TL, Klein-Schwartz W, et al. 2003 annual report of the American Association of Poison Control Centers Toxic Exposure Surveillance System. Am J Emerg Med. 2004;22(5):335-404.
6. Borron SW, Stonerook M, Reid F. Efficacy of hydroxocobalamin for the treatment of acute cyanide poisoning in adult beagle dogs. Clin Toxicol (Phila). 2006;44 Suppl 1:5-15.