What is the appropriate management of a myasthenic crisis in a patient with myasthenia gravis?

Management of Myasthenic Crisis

Immediately admit the patient to the ICU with close respiratory monitoring, initiate either plasmapheresis (5 sessions over 5 days, preferred) or IVIG (2 g/kg total over 5 days), start high-dose corticosteroids, and prepare for elective intubation if FVC <20 ml/kg or NIF <30 cmH₂O. 1, 2

Immediate Assessment and Red Flags

Apply the "20/30/40 rule" to identify imminent respiratory failure:

• Vital capacity <20 ml/kg 1, 2
• Maximum inspiratory pressure (NIF) <30 cmH₂O 1, 2
• Maximum expiratory pressure <40 cmH₂O 1, 2

Perform immediate pulmonary function testing with forced vital capacity (FVC) and negative inspiratory force (NIF) measurements upon presentation. 1, 2 The single breath count test (counting at 2 numbers per second after deep breath) can supplement formal testing, with counting to ≥25 indicating adequate respiratory function. 2

Key clinical features to assess:

• Rapidly progressive weakness of respiratory and bulbar muscles 3
• Severe dyspnea and aspiration risk 3
• Flaccid tetraparesis with immobility 3
• Globus events with exhausting coughing and swallowing 3

Critical First Steps in ICU

Secure the airway early - do not wait for emergent respiratory arrest. Elective intubation is preferred over emergent intubation when FVC <20 ml/kg or NIF <30 cmH₂O. 1 Bulbar symptoms with aspiration risk mandate early intubation to protect the airway. 1, 3

Immediately discontinue all medications that worsen myasthenia gravis:

• β-blockers 1, 2
• IV magnesium (absolutely contraindicated) 1, 2
• Fluoroquinolone antibiotics 1, 2
• Aminoglycoside antibiotics 1, 2
• Macrolide antibiotics 1, 2

Acute Immunotherapy (Choose One)

Plasmapheresis is preferred over IVIG for myasthenic crisis. 1 Standard regimen is 5 sessions over 5 days, with an alternative extended regimen of 7 exchanges over 14 days for severe cases. 2

IVIG is the alternative when plasmapheresis is contraindicated or not feasible. Dose is 2 g/kg total over 5 days (0.4 g/kg/day). 4, 1, 2 IVIG may be preferred in pregnant women. 4

Do not use sequential therapy (plasmapheresis followed by IVIG) as it is no more effective than either treatment alone. 4

Corticosteroid Therapy

Start high-dose corticosteroids concurrently with plasmapheresis or IVIG:

• Methylprednisolone 1-2 mg/kg/day IV, OR 1, 2
• Prednisone 1-1.5 mg/kg/day orally 1, 2

Begin steroid taper 3-4 weeks after initiation based on symptom improvement. 2

Pyridostigmine Management During Crisis

Discontinue or withhold pyridostigmine in intubated patients. 1, 2 For non-intubated patients with ongoing myasthenic symptoms, pyridostigmine may be continued at 30 mg orally up to 600 mg daily. 2

For patients unable to take oral medications: 30 mg oral pyridostigmine corresponds to 1 mg IV pyridostigmine or 0.75 mg neostigmine IM. 4, 2

Aggressive Respiratory Care

Implement aggressive respiratory interventions including frequent suction, intermittent positive-pressure breathing, bronchodilator treatments, sighs, and chest physiotherapy. 5 This approach reduces atelectasis and pneumonia rates (46% vs. 91% in less aggressive protocols) and shortens mechanical ventilation duration. 5

Monitor continuously for at least 24 hours in ICU, HDU, or recovery unit even after apparent stabilization. 2

Diagnostic Workup During Crisis

Obtain antibody testing:

• Acetylcholine receptor (AChR) antibodies 2
• Anti-striated muscle antibodies 2
• If AChR negative: muscle-specific kinase (MuSK) and lipoprotein-related protein 4 (LRP4) antibodies 2

Additional testing:

• CPK, aldolase, ESR, CRP to evaluate for concurrent myositis 2
• ECG and transthoracic echocardiogram if respiratory insufficiency or elevated CPK/troponin to rule out myocarditis 2

Ongoing Monitoring

Daily neurological evaluation throughout the crisis. 4, 1

Frequent pulmonary function assessments with NIF and VC measurements. 4, 1, 2

Identify and treat precipitating factors such as infections (respiratory tract infections, urinary tract infections). 1

Expected Course and Prognosis

Median duration of mechanical ventilation is 12-14 days under sufficient treatment, though approximately 20% remain ventilated after 1 month due to comorbidities and complications. 3 Mortality ranges from 2-5% to 16%, with deaths almost never caused by the crisis itself but by comorbidities or complications. 3

Lifetime risk of crisis recurrence is approximately 30%. 3 Most crises occur within the first 2 years of disease, and up to 20% of patients present with crisis as their first manifestation of myasthenia gravis. 3, 6

Common Pitfalls to Avoid

Do not rely on pulse oximetry or arterial blood gases as early indicators of respiratory failure—they are unreliable in this context. 2

Do not use noninvasive positive-pressure ventilation (NIPPV) for preventive purposes in stable myasthenia gravis patients, as studies show increased mortality with prophylactic nocturnal ventilation. 4

Do not delay intubation waiting for complete respiratory decompensation—elective intubation based on objective pulmonary function criteria prevents emergent airway complications. 1