Study guide
20.3 Toxin-Mediated Paralysis & Neuromuscular Crises: Botulism, Tetanus, Tick Paralysis & Myasthenic Crisis
ABIM Critical Care Medicine Study Guide Exam
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1 Chapter 1: Exam Orientation: Format, Blueprint & Study Strategy
1.1 ABIM Critical Care Medicine Exam: Format, Blueprint & Study Strategy
2 Chapter 2: Acute Respiratory Failure & ARDS
2.1 ARDS Definition, Pathophysiology & Phenotypes 2.2 Lung-Protective Mechanical Ventilation 2.3 Refractory ARDS: Prone Positioning, Neuromuscular Blockade & VV-ECMO
3 Chapter 3: Obstructive Airways, Pulmonary Vascular & Pleural Emergencies
3.1 Severe Asthma & COPD Exacerbations in the ICU 3.2 Massive & Submassive Pulmonary Embolism 3.3 Pulmonary Hypertension & Right Ventricular Failure in the ICU 3.4 Massive Hemoptysis, Complex Pleural Effusions & Thoracic Drainage
4 Chapter 4: Airway, Parenchymal & Nonthrombotic Pulmonary Emergencies
4.1 Airway Management, Upper-Airway Obstruction & Artificial-Airway Complications 4.2 Diffuse Alveolar Hemorrhage, Interstitial Lung Disease, Pulmonary Vasculitis & Noncardiogenic Edema 4.3 Severe Community-Acquired & Viral Pneumonia 4.4 Nonthrombotic Embolism (Air, Fat, Amniotic Fluid, Tumor, Septic) & Acute Chest Syndrome
5 Chapter 5: Mechanical Ventilation Modes, Dyssynchrony & Liberation
5.1 Mechanical Ventilator Modes & Advanced Breath Delivery 5.2 Patient-Ventilator Dyssynchrony & Waveform Analysis 5.3 Ventilator Liberation, Spontaneous Breathing Trials & Post-Extubation Support
6 Chapter 6: Shock Syndromes & Hemodynamic Principles
6.1 Shock Classification, Cellular Pathophysiology & Biomarkers 6.2 Hemodynamic Monitoring: Arterial Lines, CVP & Pulmonary Artery Catheter 6.3 Dynamic Assessment of Fluid Responsiveness & Resuscitation Targets
7 Chapter 7: Vasoactive Therapies & Mechanical Circulatory Support
7.1 Vasopressors & Inotropes: Pharmacology & Clinical Titration 7.2 Temporary Mechanical Circulatory Support: IABP, Impella & TandemHeart 7.3 Venoarterial ECMO (VA-ECMO) & Differential Hypoxemia 7.4 Post-Cardiac Arrest Care, Targeted Temperature Management & Neuroprognostication
8 Chapter 8: Acute Kidney Injury & Renal Replacement Therapy
8.1 KDIGO AKI Classification, Etiologies & Diagnostic Evaluation 8.2 Continuous Renal Replacement Therapy (CRRT) vs Intermittent Hemodialysis 8.3 Indications & Timing for RRT in Critical Illness: AKIKI & STARRT-AKI
9 Chapter 9: Electrolyte, Acid-Base & Endocrine Emergencies
9.1 Severe Dysnatremias: Hyponatremia, Hypernatremia & Osmotic Demyelination 9.2 Potassium, Calcium, Magnesium & Phosphate Disorders 9.3 Complex & Mixed Acid-Base Disorders: Boston vs Copenhagen vs Stewart 9.4 Endocrine Crises: DKA, HHS, Thyroid Storm, Myxedema Coma & Adrenal Crisis
10 Chapter 10: Glycemic Control, Hyperammonemia, Pituitary & Adrenal Disorders
10.1 ICU Glycemic Control & Severe Hypoglycemia 10.2 Non-Hepatic Hyperammonemia & Metabolic Encephalopathy 10.3 Pituitary Emergencies, Adrenal Excess & Critical Illness-Related Corticosteroid Insufficiency
11 Chapter 11: Acute Coronary Syndromes & Cardiac Arrhythmias
11.1 Acute Coronary Syndromes & Mechanical Complications of Myocardial Infarction 11.2 Critical Tachyarrhythmias: Atrial Fibrillation with RVR, VT & VF 11.3 Critical Bradyarrhythmias, Conduction Blocks & Temporary Cardiac Pacing
12 Chapter 12: Acute Heart Failure, Valvular & Pericardial Emergencies
12.1 Acute Decompensated Heart Failure & Cardiogenic Pulmonary Edema 12.2 Acute Valvular Regurgitation & Prosthetic Valve Emergencies 12.3 Pericardial Tamponade & Acute Aortic Syndromes
13 Chapter 13: Myocardial Disease, Hypertensive & Cardiac Device Emergencies
13.1 Fulminant Myocarditis, Stress & Peripartum Cardiomyopathy, and Hypertrophic Cardiomyopathy 13.2 Hypertensive Emergencies & Ruptured Abdominal Aortic Aneurysm 13.3 Implanted Cardiac Devices, LVAD Emergencies & Electrical Storm
14 Chapter 14: Sepsis & Systemic Infectious Diseases
14.1 Sepsis-3 Definitions & Surviving Sepsis Campaign 2026 Guidelines 14.2 Refractory Septic Shock & Adjunctive Therapies 14.3 Multidrug-Resistant Pathogens & Antimicrobial Stewardship in the ICU
15 Chapter 15: ICU-Acquired & Severe Focal Infections
15.1 Hospital-Acquired & Ventilator-Associated Pneumonia 15.2 Central Line-Associated Bloodstream Infections & Catheter-Associated UTIs 15.3 Intra-Abdominal Sepsis, Necrotizing Soft Tissue Infections & CNS Infections
16 Chapter 16: Focal, Special-Host & Systemic Infections
16.1 CNS Infections Beyond Bacterial Meningitis: Encephalitis, Brain Abscess & Epidural Abscess 16.2 Infections in the Immunocompromised Host, Tropical & Bioterror Infections 16.3 Infective Endocarditis, Device Infections & Other Focal Cardiovascular Infections 16.4 Antimicrobial Pharmacokinetics, Allergy, Toxicity & Infection Prevention 16.5 Gastrointestinal & Hepatobiliary Infections: Fulminant C. difficile, Typhlitis, CMV Colitis & Abscesses
17 Chapter 17: Neurocritical Care & Coma
17.1 Coma, Altered Mental Status & Acute Delirium in the ICU 17.2 Status Epilepticus & Non-Convulsive Status Epilepticus 17.3 Acute Ischemic Stroke & Intracranial Hemorrhage
18 Chapter 18: Cerebrovascular Syndromes, Encephalopathy & Withdrawal States
18.1 Cerebral Venous Sinus Thrombosis, PRES & Reversible Cerebral Vasoconstriction Syndrome 18.2 Alcohol & Sedative Withdrawal, Wernicke Encephalopathy & Drug-Induced Encephalopathy
19 Chapter 19: Intracranial Hypertension & Neuromuscular Weakness
19.1 Intracranial Pressure Monitoring, Cerebral Perfusion & Tiered ICP Management 19.2 Acute Neuromuscular Respiratory Failure, ICU-Acquired Weakness & Brain Death Determination
20 Chapter 20: Traumatic Brain Injury, Spinal Cord Injury & Toxin-Mediated Paralysis
20.1 Traumatic Brain Injury Management & Paroxysmal Sympathetic Hyperactivity 20.2 Acute Spinal Cord Injury, Neurogenic Shock & Autonomic Dysreflexia 20.3 Toxin-Mediated Paralysis & Neuromuscular Crises: Botulism, Tetanus, Tick Paralysis & Myasthenic Crisis
21 Chapter 21: Gastrointestinal, Hepatic & Abdominal Emergencies
21.1 Acute Upper & Lower Gastrointestinal Bleeding in the ICU 21.2 Acute Liver Failure & Severe Acute Pancreatitis 21.3 Abdominal Compartment Syndrome & Acute Mesenteric Ischemia
22 Chapter 22: Luminal GI Emergencies & Complications of Cirrhosis
22.1 Esophageal, Gastric & Bowel Emergencies: Perforation, Obstruction, Ogilvie Syndrome & Colonic Ischemia 22.2 Complications of Cirrhosis: Alcohol-Associated Hepatitis, Hepatorenal Syndrome & Pulmonary Vascular Syndromes
23 Chapter 23: Trauma, Burns & Perioperative Critical Care
23.1 Polytrauma Resuscitation, Damage Control & Massive Transfusion 23.2 Severe Burn Injury, Inhalation Injury & Environmental Emergencies 23.3 Perioperative Critical Care for High-Risk Surgical Patients
24 Chapter 24: Thoracic Trauma, Environmental Injury & Obstetric Critical Care
24.1 Thoracic Trauma: Flail Chest, Pulmonary Contusion, Great Vessel & Tracheobronchial Injury 24.2 Environmental Injury: Drowning, Diving, Altitude, Heat, Cold, Electrical & Radiation 24.3 Obstetric & Genitourinary Emergencies and the Physiology of Pregnancy
25 Chapter 25: Transplantation, Donor Management & Post-Cardiac Surgery Care
25.1 Solid Organ Transplant Recipients & Deceased Donor Management 25.2 Post-Cardiac Surgery Critical Care: Bleeding, Tamponade, Low Output & Vasoplegia
26 Chapter 26: Hematologic Emergencies, Toxicology, Critical Ultrasound & ICU Liberation
26.1 Hematologic Emergencies in the ICU: HIT, DIC, TMA & Anticoagulant Reversal 26.2 Critical Care Toxicology, Toxidromes & Specific Antidotes 26.3 Critical Care Point-of-Care Ultrasound (POCUS) 26.4 ICU Liberation, Analgosedation, Goals of Care & Critical Care Ethics
27 Chapter 27: Transfusion Medicine, Hematologic & Oncologic Disorders
27.1 Transfusion Medicine: Products, Thresholds, Reactions & Apheresis 27.2 Red and White Cell Disorders, Hemoglobinopathies, Factor Deficiencies & Hypercoagulable States 27.3 Oncologic Emergencies, Hematopoietic Cell Transplant Complications & Cellular Therapy Toxicity
28 Chapter 28: Clinical Pharmacology, Adverse Drug Reactions & Specific Poisonings
28.1 Pharmacokinetic Principles, Dose Adjustment & Drug Interactions in Critical Illness 28.2 Adverse Drug Reactions: Anaphylaxis, Severe Cutaneous Reactions & Hyperthermic Syndromes 28.3 Specific Poisonings: Sodium-Channel Blockers, Lithium, Valproate, Theophylline, Iron, Sulfonylureas & Methemoglobinemia
29 Chapter 29: Ethics, Research Methods, Administration & Abdominal Ultrasound
29.1 Advance Care Planning, Nonbeneficial Treatment, Informed Consent & Confidentiality 29.2 Critical Care Research Methods, Statistics, IRB Oversight & Quality Improvement 29.3 Abdominal, Vascular & Procedural Point-of-Care Ultrasound
20.3 Toxin-Mediated Paralysis & Neuromuscular Crises: Botulism, Tetanus, Tick Paralysis & Myasthenic Crisis
Key Takeaways Explain This Topic AI
Botulism produces symmetric descending paralysis beginning with cranial nerve findings, a clear sensorium, and no sensory loss; antitoxin is given on clinical suspicion before confirmation.
Equine heptavalent botulinum antitoxin is used for adults, whereas human-derived botulism immune globulin (BabyBIG) is for infant botulism.
Tetanus is treated with wound debridement, metronidazole (preferred over penicillin), human tetanus immune globulin, and spasm control with benzodiazepines or magnesium sulfate.
Myasthenic crisis is treated with intravenous immunoglobulin or plasma exchange plus corticosteroids, and acetylcholinesterase inhibitors are often held during mechanical ventilation to reduce secretions.
Tick paralysis causes an ascending flaccid paralysis that resolves after tick removal, with no antitoxin required.
Last updated: October 2026
Botulism
Botulinum toxin cleaves the SNARE proteins required for presynaptic acetylcholine release at both the neuromuscular junction and autonomic synapses.
Forms : foodborne (home-canned foods), wound botulism (injection drug use, particularly black tar heroin), infant botulism (honey, spores), iatrogenic (cosmetic or therapeutic injection), inhalational (bioterrorism), and adult intestinal colonization.
Classic features :
Symmetric, descending paralysis that starts with the cranial nerves: diplopia, ptosis, blurred vision from fixed dilated pupils, dysarthria, dysphagia, and facial weakness.
Clear sensorium and no sensory loss .
Afebrile , unless there is a wound infection.
Autonomic (anticholinergic) features : dry mouth, ileus, urinary retention, and orthostatic hypotension.
Progressive respiratory failure from bulbar and diaphragmatic weakness.
Differential : Guillain-Barré syndrome and its Miller Fisher variant (ascending, with areflexia and albuminocytologic dissociation in the CSF), myasthenia gravis (fatigable, responds to acetylcholinesterase inhibitors), Lambert-Eaton syndrome (incremental response on repetitive stimulation), tick paralysis, organophosphate poisoning, and stroke.
Confirmation : toxin assay (mouse bioassay) and culture of serum, stool, gastric contents, or wound; electrodiagnostic studies show a low compound muscle action potential amplitude with facilitation after high-frequency repetitive stimulation or exercise .
Treatment :
Antitoxin immediately on clinical suspicion , because it only neutralizes toxin that is still circulating and cannot reverse paralysis already established. Equine heptavalent antitoxin (types A to G) is used in adults and children, obtained through public health authorities; human-derived botulism immune globulin (BabyBIG) is used for infant botulism. Watch for hypersensitivity to equine product.
Monitor and support ventilation : follow vital capacity and negative inspiratory force; intubate for bulbar failure or falling vital capacity.
Wound botulism : debride the wound and give antibiotics (penicillin or metronidazole). Avoid aminoglycosides and clindamycin, which impair neuromuscular transmission.
Supportive care for weeks to months, because recovery requires regeneration of nerve terminals. Report to public health immediately.
Do not use acetylcholinesterase inhibitors as therapy; they are ineffective.
Tetanus
Tetanospasmin blocks the release of inhibitory glycine and GABA from spinal interneurons, removing inhibition of motor neurons and sympathetic outflow.
Presentation : trismus (lockjaw) and risus sardonicus, neck and back rigidity progressing to opisthotonus , and generalized spasms triggered by light, noise, or touch in a fully conscious patient. Laryngeal spasm causes sudden asphyxia.
Autonomic instability emerges in the second week: labile hypertension and tachycardia alternating with bradycardia and hypotension, sweating, and arrhythmias.
Clinical diagnosis : there is no confirmatory test, and a wound is not always found. Neonatal tetanus follows unsterile cord care.
Management :
Wound debridement .
Metronidazole (preferred; penicillin is a GABA antagonist and is a second choice).
Human tetanus immune globulin (3,000 to 6,000 units IM, part infiltrated around the wound) to neutralize unbound toxin; intrathecal administration is used in some settings.
Spasm control : high-dose benzodiazepines (diazepam or midazolam infusions) and magnesium sulfate , which reduces spasms and autonomic instability. Intrathecal baclofen is an option.
Neuromuscular blockade and mechanical ventilation for spasms refractory to sedation; secure the airway early, often with tracheostomy , because laryngospasm is lethal and the course lasts weeks.
Autonomic instability : magnesium, labetalol or esmolol (avoid short-acting beta-blockade without alpha coverage in severe cases), morphine, and clonidine or dexmedetomidine.
A dark, quiet environment with clustered care; nutrition support for a very high metabolic rate; thromboprophylaxis.
Immunize : natural infection does not confer immunity, so give the tetanus toxoid series during recovery.
Tick Paralysis
Mechanism : a salivary neurotoxin from an attached female tick ( Dermacentor species in North America; Ixodes holocyclus in Australia, which can worsen after removal).
Presentation : ascending, symmetric flaccid paralysis with areflexia over days, often with ataxia, in a child or adult with an attached tick (frequently hidden in hair). Sensation and sensorium are preserved; fever is absent.
Diagnosis : find the tick. Examine the scalp, behind the ears, the axillae, and the groin carefully.
Treatment : remove the tick ; recovery usually begins within hours to days in North American cases. Supportive ventilation is sometimes required. Antitoxin exists for the Australian species. No antibiotic is needed for paralysis itself.
Myasthenic Crisis Versus Cholinergic Crisis
Myasthenic crisis is respiratory failure from myasthenia gravis requiring ventilatory support.
Triggers : infection, surgery, aspiration, pregnancy, tapering immunosuppression, and drugs : aminoglycosides, macrolides, fluoroquinolones, telithromycin, magnesium, beta-blockers, calcium-channel blockers, iodinated contrast, neuromuscular blockers, and immune checkpoint inhibitors .
Monitoring : forced vital capacity below about 15 to 20 mL/kg , negative inspiratory force weaker than about −20 to −30 cmH2O, bulbar weakness with secretions, and a rising PaCO2 all indicate intubation. Do not wait for hypoxemia.
Noninvasive ventilation (BiPAP) can avert intubation in selected patients with hypercapnia but not severe bulbar dysfunction and secretions.
Treatment :
Plasma exchange or IVIG ; plasma exchange may work faster in crisis, and the two are broadly comparable in trials.
Corticosteroids , recognizing a possible transient worsening in the first days.
Start or optimize longer-term immunosuppression (azathioprine, mycophenolate, rituximab, complement inhibitors, FcRn antagonists).
Hold or reduce acetylcholinesterase inhibitors while intubated, because they increase secretions and offer little benefit during ventilation.
Treat the trigger and stop offending drugs.
For intubation, use a reduced dose of a nondepolarizing agent (patients are very sensitive) or avoid paralytics; succinylcholine requires higher doses and is generally avoided.
Cholinergic crisis results from excess acetylcholinesterase inhibitor and causes weakness with muscarinic excess : miosis, salivation, lacrimation, bronchorrhea, diarrhea, bradycardia, and fasciculations. Treat by withholding the inhibitor and giving atropine for secretions. The distinction matters because the treatments are opposite; in modern practice, myasthenic crisis is far more common.
Thymectomy is beneficial in generalized acetylcholine receptor antibody-positive myasthenia and is arranged after recovery, not during crisis.