Myasthenic Crisis: Recognition and Emergency Management

The myasthenic crisis is one of those neuromuscular emergencies that rarely occurs in everyday clinical practice but can rapidly become life-threatening when it does. Approximately 15–20% of all patients with myasthenia gravis experience at least one myasthenic crisis during the course of their disease. Despite modern intensive care medicine, mortality remains at 3–8%, but rises drastically when diagnosis is delayed or airway management is initiated too late. For you as an emergency physician, anesthesiologist, or intensivist, it is crucial to recognize the clinical signs early, establish the correct differential diagnosis, and implement a structured treatment plan.

Pathophysiology in Brief

Myasthenia gravis is an autoimmune disease of the neuromuscular junction. Autoantibodies — directed against the nicotinic acetylcholine receptor (AChR) in approximately 85% of cases, and less commonly against muscle-specific tyrosine kinase (MuSK) or LRP4 — block, destroy, or modulate postsynaptic signal transmission. The result is exertion-dependent muscle weakness that partially recovers with rest.

In a myasthenic crisis, neuromuscular transmission deteriorates so severely that the respiratory muscles — the diaphragm, intercostal muscles, and accessory muscles of respiration — fail. The transition from a severe exacerbation to a full-blown crisis is often gradual. By definition, a myasthenic crisis is present when respiratory insufficiency requires mechanical ventilation or intubation is imminent.

Trigger Factors: What Causes the Crisis?

In many cases, a triggering factor can be identified. A systematic search for triggers is part of the initial diagnostic workup and influences further therapy.

Common Triggers

• Infections: Respiratory and urogenital infections are the most common triggers. Even a simple upper respiratory tract infection can lead to decompensation in myasthenia patients.
• Medications: Numerous substances can impair neuromuscular transmission:
  • Aminoglycosides (gentamicin, tobramycin)
  • Fluoroquinolones (ciprofloxacin, levofloxacin)
  • Macrolides (azithromycin, erythromycin)
  • Beta-blockers (including timolol eye drops)
  • Intravenous magnesium
  • Phenytoin, lithium
  • Neuromuscular blocking agents (especially non-depolarizing agents)
  • Checkpoint inhibitors (nivolumab, pembrolizumab)
• Reduction or discontinuation of immunosuppression: Too rapid dose reduction of corticosteroids, azathioprine, or mycophenolate mofetil can trigger a crisis.
• Surgical procedures: Especially thymectomy, but also other surgeries under general anesthesia.
• Emotional or physical stress: Including sleep deprivation, heat, and pregnancy.
• Initial presentation: In approximately 20% of cases, the myasthenic crisis is the first manifestation of the disease — here, the anamnestic warning is absent.

No Trigger Identifiable

In up to one-third of patients, no clear trigger can be found. This should not prevent you from making the diagnosis when the clinical presentation fits.

Clinical Recognition: Warning Signs and Red Flags

Clinical deterioration typically progresses over hours to a few days. Less commonly, a fulminant course develops within minutes.

Typical Symptoms and Findings

• Progressive dyspnea, especially when supine (orthopnea due to diaphragmatic weakness)
• Tachypnea with decreasing tidal volumes
• Use of accessory muscles of respiration, paradoxical abdominal breathing
• Weakening of cough and swallowing reflexes — aspiration risk
• Bulbar symptoms: nasal speech, dysphagia, drooling
• Generalized muscle weakness with head drop and limb weakness
• Ptosis and diplopia (often pre-existing, but worsening)

Objective Parameters

• Vital capacity (VC): A decline below 20 mL/kg body weight is a warning sign; below 15 mL/kg body weight is an indication for intubation. Serial bedside vital capacity measurements (bedside spirometry) are an indispensable monitoring tool.
• Maximum inspiratory pressure (MIP/NIF): Values worse than −30 cmH₂O indicate severe diaphragmatic weakness.
• Peak cough flow: Below 160 L/min, cough effectiveness is so impaired that secretion clearance can no longer be guaranteed.
• Arterial blood gas analysis: Hypercapnia (pCO₂ > 45 mmHg) is a late sign. Do not wait for blood gas deterioration — clinical assessment and spirometry values must guide your decision.

The "20/30/40 Rule" as a Clinical Mnemonic

Consider intubation when:

• Vital capacity < 20 mL/kg body weight
• MIP worse than −30 cmH₂O
• MEP (maximum expiratory pressure) < 40 cmH₂O

These values do not replace clinical judgment but provide a useful framework for decision-making.

Myasthenic Crisis vs. Cholinergic Crisis: The Critical Differential Diagnosis

The distinction between myasthenic and cholinergic crisis is clinically fundamental, as the therapeutic consequences are diametrically opposed.

Feature	Myasthenic Crisis	Cholinergic Crisis
Cause	Worsening of myasthenia	Overdose of cholinesterase inhibitors
Pupils	Normal to dilated	Constricted (miosis)
Salivation	Minimal	Pronounced (hypersalivation)
Fasciculations	None	Common
Diarrhea, nausea	No	Yes (muscarinic symptoms)
Sweating	Minimal	Pronounced
Bradycardia	Rare	Common
Response to edrophonium	Improvement	Worsening

Regarding the Edrophonium Test (Tensilon Test)

The edrophonium test is controversially discussed in the acute crisis setting. In the intensive care literature, it is increasingly recommended with caution, as it can be risky in severe respiratory insufficiency and the distinction is usually possible based on clinical presentation and history. If performed: edrophonium 2 mg IV as a test dose, then up to 8 mg IV. Atropine must be available as an antidote. In the acute crisis, the rule is: when in doubt, discontinue all cholinesterase inhibitors — this is the safer approach in both types of crisis.

Practical Tip

In modern intensive care medicine, a purely cholinergic crisis has become rare, as pyridostigmine dosing is now handled more conservatively. Mixed presentations are more commonly encountered. The pragmatic consequence: in any form of crisis, temporarily discontinue cholinesterase inhibitors and stabilize the respiratory situation.

Emergency Management: A Structured Approach

1. Airway Management and Ventilation

Airway management takes absolute priority. The following approach is recommended:

• Non-invasive ventilation (NIV): Can be used as bridging in cooperative patients with intact protective reflexes. BiPAP in particular (IPAP 10–15 cmH₂O, EPAP 4–6 cmH₂O) can reduce the work of breathing. Close monitoring is mandatory — if no improvement within 1–2 hours or blood gas deterioration occurs: intubate.
• Endotracheal intubation: In the presence of bulbar symptoms with aspiration risk, exhaustion, or when vital capacity falls below 15 mL/kg body weight. Special caution is required regarding the choice of neuromuscular blocking agent for intubation:
  • Succinylcholine: Patients with myasthenia gravis are relatively resistant to succinylcholine (increased ED₉₅). The usual dose of 1 mg/kg body weight is often insufficient; 1.5–2 mg/kg body weight may be required. Nevertheless, the response is poorly predictable.
  • Non-depolarizing agents: Extremely increased sensitivity! If necessary, use rocuronium in a significantly reduced dose (0.3–0.5 mg/kg body weight instead of 0.6 mg/kg body weight) with sugammadex as a reversal option.
  • Ideal scenario: Intubation without neuromuscular blocking agents, provided the depth of anesthesia allows it (e.g., with propofol and remifentanil).
• Ventilation: Lung-protective ventilation with tidal volumes of 6–8 mL/kg IBW. Weaning may be prolonged — plan for tracheostomy early if extubation is not foreseeable after 10–14 days.

2. Discontinue Cholinesterase Inhibitors

Pyridostigmine and other cholinesterase inhibitors are discontinued during the acute crisis. The rationale:

• Eliminates uncertainty regarding a cholinergic component
• Reduces bronchial secretions (facilitates ventilation)
• Avoids bradycardia and gastrointestinal complications

Reintroduction occurs after stabilization, typically at a reduced dose with gradual titration.

3. Acute Immunomodulatory Therapy

The two cornerstones of acute immunomodulatory therapy are intravenous immunoglobulins (IVIG) and plasmapheresis (PE) or immunoadsorption (IA). Both modalities are comparable in efficacy — the choice depends on availability, contraindications, and local expertise.

Intravenous Immunoglobulins (IVIG)

• Dosing: 0.4 g/kg body weight/day over 5 days (total dose 2 g/kg body weight)
• Onset of action: After 3–5 days, maximum effect after 1–2 weeks
• Advantages: Widely available, no central venous access required, no loss of coagulation factors
• Disadvantages/Risks: Headache, nausea, anaphylactoid reactions (especially in IgA deficiency), thromboembolism, aseptic meningitis, renal insufficiency (particularly with sucrose-containing preparations)
• Contraindications: Known IgA deficiency with anti-IgA antibodies, severe renal insufficiency, hypercoagulability

Plasmapheresis (PE) / Immunoadsorption (IA)

• Protocol: Typically 5–6 sessions every other day
• Onset of action: Often faster than IVIG, initial improvement after 2–3 sessions
• Advantages: Faster onset of action, potentially superior in MuSK antibody-positive myasthenia
• Disadvantages/Risks: Central venous access required, hypotension, electrolyte disturbances, loss of coagulation factors (with PE, not with IA), infection risk
• Contraindications: Hemodynamic instability, severe sepsis, active bleeding

Immunoadsorption as an Alternative

Immunoadsorption offers the advantage of selective antibody removal without loss of coagulation factors and albumin. It is the preferred extracorporeal method in many centers.

4. Corticosteroids

Corticosteroids are a central component of long-term immunosuppression but must be used with caution in the acute crisis:

• Caution: High-dose methylprednisolone can cause a paradoxical worsening of muscle weakness in the first few days (in up to 50% of patients with severe myasthenia).
• Approach: Start only after stabilization with IVIG or PE. Choose a low starting dose (e.g., prednisolone 0.5 mg/kg body weight) and titrate slowly. Alternatively: begin corticosteroid therapy only after extubation.
• If corticosteroid therapy is already ongoing: Do not discontinue; continue the current regimen.

5. Supportive Intensive Care Measures

• Thromboprophylaxis: Immobilized patients have a high VTE risk. LMWH at prophylactic doses (e.g., enoxaparin 40 mg s.c. once daily).
• Aspiration prevention: Nasogastric tube placement for severe dysphagia, head-of-bed elevation to 30°.
• Infection screening and treatment: Actively search for and treat infections as the most common trigger. When selecting antibiotics, observe the contraindication list — penicillins, cephalosporins, and carbapenems are considered safe.
• Nutrition: Initiate enteral nutrition via nasogastric tube early when oral intake is not possible.
• Physiotherapy: Early mobilization and respiratory physiotherapy as soon as the patient's condition allows.

Complications and Prognosis

The most common complications of myasthenic crisis are:

• Ventilator-associated pneumonia: Risk increases with duration of mechanical ventilation
• Atelectasis: Due to diaphragmatic weakness and secretion retention
• Thromboembolism: Due to immobilization
• Prolonged weaning: Median duration of mechanical ventilation is 10–14 days

Prognosis has significantly improved with modern intensive care medicine. The majority of patients recover from the acute crisis, though often with residual impairment requiring adjustment of long-term immunosuppressive therapy.

Summary: Algorithm at a Glance

1. Recognition: Progressive dyspnea, bulbar symptoms, vital capacity < 20 mL/kg body weight → consider myasthenic crisis
2. Airway management: NIV as bridging, intubation if NIV fails or aspiration risk is present. Avoid neuromuscular blocking agents or dose with caution.
3. Discontinue cholinesterase inhibitors
4. Trigger search: Infection? Medication? Change in therapy?
5. Initiate immunomodulation: IVIG 0.4 g/kg/day over 5 days OR plasmapheresis/immunoadsorption (5–6 sessions)
6. Corticosteroids: Only after stabilization, with gradual dose escalation
7. Basic intensive care measures: Thromboprophylaxis, aspiration prevention, infection treatment, nutrition, physiotherapy
8. Neurology consultation: Involve early for long-term therapy planning

Practical Training

The myasthenic crisis is a rare but highly relevant scenario that requires structured action under time pressure — from clinical recognition to the delicate airway management to differentiated pharmacotherapy. In the emergency physician refresher course offered by Simulation Tirol, you can train such neuromuscular emergency scenarios in a realistic simulation environment, refresh your knowledge of ventilation indications and airway management, and prepare as a team for situations where standard algorithms alone are not sufficient. For more information, visit simulation.tirol.