Toxidromes

Hyperthermic Toxidromes; Serotonin Syndrome, Malignant Hyperthermia, and Neuroleptic Malignant Syndrome

• Temperature > 38.5–39°C. Altered sensorium ± rigidity ± autonomic instability

• Excess serotonin (5HT1A/B) -> SS [CNS excitation => neurologica hyperactive]

• Dopamine blockade [D2 receptor] -> NMS [Dopamine motor suppression => centrally suppressed but rigid]

• Uncontrolled Ca2+ release -> MH [Peripheral muscle defect]

• Different triggers. Same terminal physiology. The final common pathway -> Skeletal muscle contraction + autonomic dysfunction

• All causes ↑ Muscle activity → ↑ ATP consumption → ↑ Heat → Rhabdomyolysis → Hyperkalemia → Organ failure

• Antipyretics are useless in all three (This is heat from muscle activity, not fever). Cooling + muscle control is life-saving.

Clinical difference

1. SS -> Hyperthemia + Agitation + Clonus [Hunter criteria] & Hypereflexia of LL.  (hours) ; Mod CK

2. NMS -> Hyperthermia + Lead-pipe Rigid + Antipsychotic history.  (days/slow onset) ; high CK

3. MH -> Intraoperative + sudden ETCO2 spike.   (minutes) ; Very high CK + Hyperkalemia

Typical trigger (& Treatment drug)

• SS -> Fluoxetine/Linezolid/tramadol 

Rx; oral Cyproheptadine + Benzodiazapine

• NMS -> Haloperidol 

Rx; Bromocriptine; dopamien blocker / Dadnrolene 

• MH -> Succinyl Scoline 

Rx; iv Dantrolene + Treat hyperkalemia; Mechanism: Ryanodine receptor mutation

Ryanodine receptor (RyR): It functions as the primary calcium-release channel in the sarcoplasmic reticulum (SR) of muscle cells and the endoplasmic reticulum (ER) of other tissues. It is the largest known ion channel. 

The RyR facilitates the rapid release of stored calcium ions into the cytosol, a process essential for excitation-contraction (E-C) coupling.

• Skeletal Muscle (RyR1): Triggered by a direct physical interaction with the voltage-sensing dihydropyridine receptor (DHPR) in the T-tubule membrane. [L-type Ca channel]

• Cardiac Muscle (RyR2): Activated by a small influx of calcium through L-type calcium channels, which then triggers a massive release of SR calcium—a process known as Calcium-Induced Calcium Release (CICR)

Ryanodine: A plant alkaloid that gave the receptor its name. 

Dantrolene: An antagonist used clinically to treat Malignant Hyperthermia (MH) and NMS

The RyR acts as a scaffold for numerous modulators, including calmodulin

Mutations in RyR genes (often called "Ryanopathies") cause severe disorders:

1. RyR1: Linked to Malignant Hyperthermia (triggered by anaesthetics) and Central Core Disease (muscle weakness).

2. RyR2: Associated with life-threatening cardiac arrhythmias like Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) and Heart Failure.

Condition Receptor Mechanism Key Triggers / Features

1. Malignant Hyperthermia (MH)

   • • RyR1 Gain-of-function mutation; excessive release leads to hypermetabolism.

     • Triggers; Volatile anaesthetics (e.g., halothane, isoflurane) or succinylcholine.

2. Central Core Disease (CCD)

   • • RyR1 Typically loss-of-function mutation; it leads to muscle weakness and "cores" on muscle biopsy.

     • Congenital myopathy; strong clinical link to MH susceptibility.

3. Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT)

   • • RyR2 Gain-of-function; diastolic leak causes delayed after-depolarisations (DADs).

     • Trigger: Exercise or emotional stress (catecholamine surge); presents as syncope or sudden death in young patients.

4. Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC Type 2)

   • • RyR2 Mutations lead to myocyte replacement with fibro-fatty tissue.

     • Trigger: Ventricular arrhythmias and right heart failure.

Hyperthermia Approach

• Clonus + Hyperreflexia (LL>UL) → SEROTONIN SYNDROME

• Lead-pipe rigidity + antipsychotic history + slow onset → NMS

• Intraoperative + sudden ETCO₂ rise + severe acidosis → MH

Clue;

• Linezolid + SSRI → Serotonin syndrome

• Dopamine withdrawal in Parkinson’s → NMS

• Antipyretics are ineffective in all three

• Hyperthermia is due to muscle activity, not hypothalamic set-point change

• Lower limb hyperreflexia strongly favours SS

• Clonus = Serotonin

• Lead-pipe rigidity = NMS

• ETCO₂ spike = MH

• Dry skin = Anticholinergic

• Very high BP + cocaine history = Sympathomimetic

• MDMA can cause sympathomimetic toxidrome + severe hyponatremia (SIADH/excess water)

• Hypotension + lactate + no neuromuscular signs = Sepsis

Toxidromes:

1. Sympathomimetic (Excess catecholamine)

   1. 1. • Examples: Cocaine / Amphetamine / MDMA

         • Pattern: Agitation / Tachycardia / Hypertension / Sweaty /Mydriasis / Hyperthermia

         • First-line: Benzodiazepine, Active cooling, Avoid pure β-blockers (risk unopposed α)

2. Anticholinergic (Muscarinic receptor blockade)

   1. 1. • Examples: Amitriptyline / Diphenhydramine / Atropine

         • Pattern: Hot as a hare/Blind as a bat/Dry as a bone/Red as a beet/Mad as a hat

         • Benzodiazepines, Cooling, Sodium bicarbonate if TCA (QRS widening), Physostigmine (selected cases)

3. Serotonin syndrome (Excess serotonin (5-HT1A/2A))

• Triggers: Fluoxetine, Linezolid

• Pattern: Rapid onset (hours)/Clonus/Hyperreflexia (legs > arms)

• Benzodiazepines, Cooling, Cyproheptadine

4. Neuroleptic Malignant Syndrome (Dopamine blockade)

• Trigger: Haloperidol

• Pattern: Slow onset (days), Lead-pipe rigidity, High CK

• Cooling, IV fluids, Dantrolene

5. Opioid

• Examples: Morphine, Heroin

• Pattern: ↓ Respiratory rate, Pinpoint pupils, ↓ LOC, Hypotension

• Airway support, Naloxone

6. Cholinergic (Organophosphate; Acetylcholinesterase inhibition)

• Examples: Malathion

• Pattern (SLUDGE): Salivation, Lacrimation, Urination, Diarrhea, GI cramps, Emesis, Bronchorrhea, Bradycardia, Miosis

• Atropine, Pralidoxime

Dry + delirium + urinary retention → Anticholinergic

Clonus → Serotonin

Rigid + slow onset → NMS

Pinpoint + slow breathing → Opioid

Sweaty + very hypertensive → Sympathomimetic

Wet + bradycardic → Cholinergic

Cheese Reaction (Hypertensive Crisis with MAO Inhibitors)

The cheese reaction is an acute hypertensive crisis triggered by ingestion of tyramine-rich foods in patients taking monoamine oxidase inhibitors (MAOIs). Tyramine is an indirect sympathomimetic amine found in aged/fermented foods.

Normally, Tyramine is metabolised by MAO-A in the gut and liver. If the patient is on MAOI (e.g. Phenelzine or Tranylcypromine):

→ Tyramine is not broken down

→ Enters systemic circulation

→ Displaces norepinephrine from presynaptic vesicles

→ Massive catecholamine release (note: It does not directly stimulate receptors)

→ Severe hypertension

This is a sympathomimetic surge, not serotonin syndrome. Here, reflexes will be normal

May mimic: Pheochromocytoma crisis / Cocaine toxicity

Treatment (hypertension); 

• IV phentolamine (alpha-blocker)

• Nitroprusside infusion

• Nicardipine

• Avoid: Pure beta-blockers alone (unopposed alpha effect)

• Do NOT give pure beta-blocker → risk unopposed alpha vasoconstriction

• No clonus → no serotonin syndrome

• No rigidity → not NMS

• Cyproheptadine treats serotonin syndrome, not hypertensive crisis

  1. 1. 1. • MAOI + cheese → Hypertensive crisis (cheese reaction)

           • SSRI + MAOI → Serotonin syndrome

Coccain Vs Tyramine

• Cocaine blocks NE reuptake

• Tyramine releases stored NE

Both → hypertension (different mechanism)

SS Vs Hypertensive crisis

Linezolid is a weak MAO inhibitor

• Linezolid + SSRI → serotonin syndrome

• Linezolid + tyramine → hypertensive crisis

Both → hypertension (different mechanism)

Unopposed ⍺ phenomenon

Pure β-blocker in catecholamine surge → α vasoconstriction unopposed → worsening hypertension

Seen in:

• Cocaine toxicity

• Tyramine crisis

Hypertensive crisis (>180/120 + Target organ damage): in this context is catecholamine–excess–mediated mechanisms

1. Tyramine (cheese reaction) → Norepinephrine (NE) Release (indirect sympathomimetic)

2. Epinephrine → Adrenergic Receptor Effects

3. Cocaine → Reuptake Block [Cocaine blocks reuptake of: Norepinephrine/Dopamine/Serotonin]

Management Principle: Block α before β if catecholamine excess is suspected

1. Tyramine --> Phentolamine

2. Cocain --> Benzodiazapine

End-organ damage

• Encephalopathy

• ACS

• Aortic dissection

• Pulmonary edema

• AKI

Suspecting Catecholamine Excess

BP ≥180/120 + acute end-organ damage

Goal: ↓ MAP by ≤25% in first hour

1. episodic + sudden onset.

   • • Headache

     • Palpitations

     • Sweating

2. Vitals pattern

   • • Severe hypertension (often paroxysmal)

     • Tachycardia (sometimes arrhythmia)

     • Labile BP

     • Orthostatic hypotension (chronic excess)

3. Autonomic features

   • • Pallor (α1 vasoconstriction)

     • Tremors

     • Anxiety / panic-like state

     • Hyperglycemia

     • Dilated pupils

4. Red-flag situations

   • • Cocaine / amphetamine use

     • MAOI + tyramine ingestion

     • Adrenal mass

     • Post-intubation unexplained extreme BP surge

     • During surgery (pheochromocytoma crisis)

     • Young patient with resistant HTN

5. Differentials

   • Pain crisis

   • Hypoxia

   • Alcohol withdrawal

   • Thyroid storm

   • Serotonin syndrome

Catecholamine excess scenarios

1. Pheochromocytoma Trap

• Young patient, episodic headache + palpitations + sweating + resistant HTN.

• Trap: Starting β-blocker first.

• Rule: α-block before β-block (phenoxybenzamine → then propranolol).

Prevent unopposed α → hypertensive crisis.

2. Cocaine Chest Pain Trap

• Severe HTN + chest pain + recent cocaine use.

• Trap: Giving pure β-blocker (e.g., metoprolol).

• Correct: Benzodiazepine + GTN ± phentolamine.

Principle: Avoid unopposed α vasoconstriction.

3. MAOI + Cheese Reaction

• Patient on MAOI + severe headache after aged cheese/wine.

• Mechanism: Tyramine → NE release.

• Trap: Treating as primary migraine.

• Correct: α-blockade (phentolamine).

4. Hypertension + Bradycardia

• Very high BP + slow pulse.

• Trap: Thinking catecholamine surge.

• Correct diagnosis: Raised ICP (Cushing reflex).

• Catecholamine crisis = usually tachycardia.

5. Stress Cardiomyopathy Confusion

• Severe stress + troponin rise + ST changes + normal coronaries.

• Trap: Missing catecholamine surge link.

• Diagnosis: Takotsubo cardiomyopathy.

6. Lab Interpretation Trap

• Borderline plasma metanephrines.

• Trap: Diagnosing pheochromocytoma immediately.

• Remember: Stress, caffeine, labetalol can elevate levels.

• Confirm with repeat or 24-hr urinary metanephrines.

7. Resistant Hypertension in Young

• Patient <40 yrs + episodic HTN + adrenal mass.

• Next best step: Plasma-free metanephrines.

• Not: Immediate surgery.

8. Intraoperative Crisis

• During surgery, sudden severe HTN + arrhythmia.

• Clue: Undiagnosed pheochromocytoma.

• Management: IV phentolamine or nitroprusside.

9. Paradoxical Hypotension

• Chronic catecholamine excess → volume depletion

→ Orthostatic hypotension despite high baseline BP.

10. Most Tested Principle

• “In suspected catecholamine excess → never give isolated β-blockade.”

Drug interactions

• MAOI + SSRI → serotonin syndrome

• MAOI + tyramine → hypertensive crisis (cheese reaction)

• MAOI + TCA → severe toxicity

• MAOI + tramadol → serotonin syndrome

• MAOI + Linezolid → Serotonin syndrome OR hypertensive crisis

Hypertensive crisis causes

1. 1. Food history → cheese reaction

   2. Recreational drug → cocaine

   3. Episodic triad (headache, sweating, palpitations) → pheochromocytoma

Concept:

• Indirect sympathomimetics: Tyramine/Amphetamine

• Direct: Epinephrine

• Mixed: Ephedrine

• If vesicles empty → only direct agents work.

Drugs:

1. Phentolamine: A non-selective alpha-adrenergic blocker

   • • directly antagonising the effects of circulating catecholamines (epinephrine/norepinephrine) to cause rapid vasodilation

     • It is the most effective choice when hypertension is driven by a massive release of adrenaline/noradrenaline. Not used for routine hypertensive emergencies.

     • used in Catecholamine Crisis (Pheochromocytoma crisis, Cocaine/amphetamine toxicity

MAOI + tyramine reaction)

2. Sodium Nitroprusside: A potent nitric oxide (NO) donor. It is a "mixed" vasodilator

   • • used in General Hypertensive Emergency

     • Choose when an "instant-on, instant-off" effect is needed to precisely titrate BP in non-catecholamine cases.

     • Dangers: Cyanide toxicity (prolonged use, renal failure), ↑ ICP, Coronary steal

3. IV Nitrates (e.g., Nitroglycerin): Primarily venodilators

   • • Cardiac-Related Hypertension

     • Preferred if the patient has myocardial ischemia or pulmonary oedema, as it improves coronary flow better than nitroprusside.

4. Labetalol 

   • • Class: α1 + β blocker

     • No reflex tachycardia, Safe in most hypertensive emergencies

5. Nicardipine 

   • • Class: IV dihydropyridine CCB

     • Best For: Stroke, SAH, Most hypertensive emergencies

     • Advantage: Predictable titration, No cyanide risk

6. Esmolol

   • • Ultra short-acting β1 blocker

     • Best For: Aortic dissection, Perioperative crisis

     • Principle: Always control HR before reducing BP in dissection.

7. Hydralazine

   • • Best For: Pregnancy (pre-eclampsia)

     • Trap: Unpredictable BP drop → reflex tachycardia

     • Not first-line in most emergencies.

Situation-based selection

1. • • Pheochromocytoma   | Phentolamine 

     • Cocaine crisis     | Benzodiazepine + Nitroglycerin ± Phentolamine 

     • Aortic dissection  | Esmolol → Nitroprusside      

     • Pulmonary oedema | Nitroglycerin        

     • Stroke             | Nicardipine / Labetalol     

     • Pregnancy HTN      | Labetalol / Hydralazine   

     • General severe HTN | Nicardipine  

Never drop BP rapidly in stroke (unless >220/120 without thrombolysis).

In aortic dissection → control HR first.

Avoid nitroprusside in renal failure.

Pure β-blocker alone is contraindicated in catecholamine excess.

Focused Hypertensive Emergency Algorith

STEP 1 — Confirm Hypertensive Emergency (BP ≥ 180/120 mmHg plus acute target-organ damage:

• CNS: encephalopathy, ICH, stroke

• Cardiac: ACS, pulmonary oedema

• Renal: AKI

• Vascular: aortic dissection

• Obstetric: eclampsia

Principle: treat the organ injury, not the number.

Step 2: 

• ↓ MAP by ≤ 25% in first hour

• Then to 160/100–110 over next 2–6 h

STEP 3 — Identify the Phenotype

A) Sympathomimetic Surge: 

• Examples: Cocaine, tyramine + Phenelzine

• Clues: severe agitation, sweating, mydriasis, tachycardia

• First-line: IV benzodiazepines (reduce catecholamine drive)

• Add if needed: Phentolamine (alpha blockade) / Nicardipine infusion

• Avoid: pure beta-blockers (unopposed alpha)

B) Aortic Dissection

• Clues: tearing chest/back pain, pulse deficit

• Goal: rapid HR + BP control 

• Target HR < 60, SBP 100–120

• Drugs: IV esmolol (beta first)

• Then add nitroprusside if BP is still high

C) Acute Pulmonary Oedema

• Clues: dyspnea, crackles, CXR congestion

• Drugs: IV nitroglycerin (high dose) / Loop diuretic / Non-invasive ventilation

• Avoid aggressive fluid boluses.

D) Hypertensive Encephalopathy

• Clues: confusion, seizures, headache, papilledema

• Drugs: Nicardipine infusion/Labetalol IV bolus/Avoid rapid overcorrection → risk cerebral hypoperfusion.

E) Intracerebral Haemorrhage

• Target: SBP 140–160 (based on local protocol)

• Nicardipine or labetalol preferred.

F) Eclampsia / Severe Preeclampsia

• IV labetalol or hydralazine

• Magnesium sulfate

G) Pheochromocytoma Crisis

• Clues: episodic headache, sweating, palpitations

• Alpha blockade first (phentolamine)

• Then beta blockade if needed

Drug selection in hypertensive crisis

1. Nicardipine     | Encephalopathy, stroke

2. Labetalol       | Neuro, pregnancy

3. Nitroprusside   | Rapid titratable (careful cyanide risk)

4. Nitroglycerin   | Pulmonary edema, ACS

5. Esmolol         | Aortic dissection

6. Phentolamine    | Catecholamine crisis

7. Benzodiazepines | Stimulant-induced 

• Chest/back tearing pain → beta first (dissection)

• Wet lungs → nitrates

• Confused neuro → nicardipine

• Stimulant/agitated → benzos first

• Pregnancy → labetalol + MgSO₄