Critical Alerts

• Myasthenic crisis is a medical emergency - respiratory failure can develop rapidly
• Monitor respiratory function closely - FVC is the key parameter
• Intubate early if respiratory function declining - don't wait for arrest
• Distinguish from cholinergic crisis - excess acetylcholinesterase inhibitor
• Avoid drugs that worsen myasthenia - aminoglycosides, fluoroquinolones, beta-blockers

Key Diagnostics

• Forced vital capacity (FVC) and negative inspiratory force (NIF)
• Arterial blood gas
• Bedside pulmonary function (single breath count test)
• Acetylcholine receptor antibodies (usually known diagnosis)
• Chest imaging (aspiration, thymoma)

Emergency Treatments

• Respiratory support: Intubation if FVC <15-20 mL/kg or NIF <-20 cmH2O
• Plasmapheresis (PLEX): 5 sessions over 10-14 days
• IVIG: 2 g/kg over 2-5 days (alternative to PLEX)
• IV corticosteroids: May initially worsen - use with caution
• Hold or reduce pyridostigmine: If cholinergic crisis suspected

Myasthenic crisis is a life-threatening complication of myasthenia gravis (MG) characterized by severe weakness requiring mechanical ventilation or threatening respiratory failure. It represents a rapidly evolving worsening of myasthenic weakness, most critically affecting respiratory and bulbar muscles.

Myasthenia Gravis Overview

Crisis Definition

• Respiratory failure requiring mechanical ventilation, OR
• Respiratory insufficiency with imminent need for ventilation
• Occurs in ~15-20% of MG patients at some point

Types of Crisis

Critical Findings

"20/30/40 Rule" for Intubation

Consider intubation when:

• FVC <20 mL/kg (or <1 L absolute)
• NIF (MIP) <-30 cmH2O
• Decline of FVC >30% from baseline

Other Causes of Acute Weakness

Respiratory Failure Differential

• Pneumonia
• COPD/asthma exacerbation
• Pulmonary embolism
• Heart failure
• Aspiration

Bedside Assessment

Respiratory Monitoring

Serial Monitoring Essential

• Check FVC/NIF every 2-4 hours (or more frequently)
• Trend is as important as absolute value
• Decline of 30% from baseline is concerning

Laboratory Studies

Imaging

Tensilon (Edrophonium) Test

Rarely performed in crisis setting

• Acetylcholinesterase inhibitor challenge
• Transient improvement = myasthenic
• Worsening = cholinergic
• High risk of bradycardia, bronchospasm
• Atropine at bedside required

ICU Admission

All patients in myasthenic crisis require ICU

• Continuous respiratory monitoring
• Serial FVC/NIF measurements
• Rapid access to intubation
• PLEX or IVIG administration

Step-Down Criteria

• Extubated >48 hours
• FVC stable >25-30 mL/kg
• Improving strength
• Tolerating oral medications

Discharge Criteria

• Respiratory function stable
• Oral medications established
• Precipitant treated
• Follow-up with neurology arranged
• Patient education completed

Follow-up

Understanding Myasthenic Crisis

• Myasthenic crisis is a serious but treatable complication
• It requires hospitalization and close monitoring
• Treatment takes days to weeks to show full effect
• Most patients recover with appropriate treatment

Preventing Future Crises

• Take medications as prescribed
• Avoid known trigger medications
• Seek early treatment for infections
• Do not stop immunotherapy without medical guidance
• Avoid extreme heat and stress when possible

Warning Signs to Seek Care

• Increasing difficulty breathing
• Difficulty swallowing or choking on food
• Worsening weakness
• Fever or signs of infection
• Voice changes

Medical Alert

• Wear medical alert identification
• Carry list of medications to avoid
• Inform all healthcare providers of diagnosis

MuSK-Positive MG

• More likely to have bulbar and respiratory involvement
• Often more severe disease
• May respond better to PLEX than IVIG
• Rituximab may be beneficial

Thymoma-Associated MG

• Often more severe
• Thymectomy recommended (staged if crisis)
• May have other paraneoplastic syndromes

Pregnancy

• MG can worsen, improve, or remain stable
• Crisis risk higher in first trimester and postpartum
• IVIG preferred over PLEX
• Avoid certain immunosuppressants
• Neonatal MG in 10-20% of newborns (transient)

Post-Thymectomy

• Crisis risk highest in first few days
• Close ICU monitoring required
• Prolonged ventilatory support may be needed

Performance Indicators

Documentation Requirements

• Respiratory function (FVC, NIF) with trends
• Strength assessment (standardized scale)
• Precipitating factor identified
• Treatment plan
• Response to therapy
• Intubation parameters if applicable
• Medications reviewed for safety

Diagnostic Pearls

1. Monitor FVC, not just O2 sat - sat drops late
2. Trend matters - declining FVC is ominous
3. Head lift <5 seconds indicates severe weakness
4. Distinguish from cholinergic crisis - treatment is different
5. Look for precipitants - infection is most common

Treatment Pearls

1. Intubate early - don't wait for arrest
2. Avoid succinylcholine - use reduced-dose rocuronium
3. PLEX and IVIG are equivalent - choose based on patient factors
4. Steroids can worsen initially - use with caution in acute crisis
5. Review all medications - many drugs worsen MG

Disposition Pearls

1. All crisis patients go to ICU - no exceptions
2. Improvement takes days - expect prolonged stay
3. Neurology involvement essential for long-term planning
4. Patient education prevents future crises
5. Medical alert ID is important