What is the initial treatment for myasthenia crisis?

Initial Treatment for Myasthenic Crisis

For myasthenic crisis, immediately hospitalize the patient in the ICU with respiratory monitoring and initiate either IVIG (2 g/kg total over 5 days) or plasmapheresis (5 sessions over 5 days) along with high-dose corticosteroids, while securing the airway if respiratory compromise is present. 1, 2, 3

Immediate Assessment and Airway Management

Rapidly assess respiratory function by measuring negative inspiratory force (NIF) and vital capacity (VC) to determine the severity of respiratory compromise. 2, 3 Apply the "20/30/40 rule" to identify patients at risk of respiratory failure: vital capacity <20 ml/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O. 3

Secure the airway early if there is:

• Respiratory arrest or peri-arrest 2
• Bulbar weakness with inability to protect the airway or clear secretions 2, 4
• Rapid desaturation or inability to achieve adequate oxygenation 2
• Progressive respiratory muscle weakness despite initial treatment 2, 5

Critical pitfall: Do not delay intubation if non-invasive ventilation is failing, as deterioration in neuromuscular disease can be very sudden. 2 Bulbar dysfunction makes non-invasive ventilation failure more likely and may make it impossible. 2

Acute Immunotherapy (Choose One)

Plasmapheresis is preferred over IVIG for myasthenic crisis based on recent evidence. 4 However, both are acceptable first-line options:

Plasmapheresis (Preferred)

• Standard regimen: 5 sessions over 5 days (20-25 mL/kg per session) 3, 6
• Alternative extended regimen: 7 exchanges over 14 days for severe cases 3
• Requires specialized equipment and expertise, often necessitating transfer to tertiary centers 3

IVIG (Alternative)

• Dosing: 2 g/kg total dose administered as 0.4 g/kg/day for 5 consecutive days 1, 2, 3
• Preferred in pregnancy due to monitoring considerations with plasmapheresis 1
• Reserved for Grade 3-4 myasthenic exacerbations requiring hospitalization 1

Important: Sequential therapy (plasmapheresis followed by IVIG) is no more effective than either treatment alone and should be avoided. 1

Corticosteroid Therapy

Initiate high-dose corticosteroids concurrently with IVIG or plasmapheresis:

• Methylprednisolone: 1-2 mg/kg/day IV 2, 3
• Prednisone: 1-1.5 mg/kg/day orally (if able to take oral medications) 1, 3
• Pulse dosing for severe symptoms: Methylprednisolone 1 g/day for 5 days 2
• Begin steroid taper 3-4 weeks after initiation, based on symptom improvement 3

Anticholinesterase Management

Pyridostigmine management during crisis is nuanced:

For Non-Intubated Patients

• Continue pyridostigmine at 30 mg orally three times daily, titrating up to a maximum of 120 mg four times daily based on symptoms 1, 3
• May be continued during IVIG or plasmapheresis 1

For Intubated Patients

• Discontinue or withhold pyridostigmine once intubated 3, 7
• If parenteral administration is necessary: 1 mg IV pyridostigmine = 30 mg oral pyridostigmine = 0.75 mg neostigmine IM 1, 2, 3

Critical warning from FDA: Overdosage of pyridostigmine can result in cholinergic crisis, characterized by increasing muscle weakness that may lead to death through involvement of respiratory muscles. 7 Distinguishing myasthenic crisis from cholinergic crisis is extremely important, as increasing pyridostigmine doses during cholinergic crisis could have grave consequences. 7

Medications to Immediately Discontinue

Absolutely avoid or discontinue these medications that can worsen myasthenic weakness:

• β-blockers 3
• IV magnesium (absolutely contraindicated) 3
• Fluoroquinolone antibiotics 1, 3
• Aminoglycoside antibiotics 1, 3
• Macrolide antibiotics 1, 3

If severe hypomagnesemia requires treatment, neurology consultation is mandatory before administration. 3

Monitoring Requirements

ICU-level monitoring must include:

• Daily neurological evaluation 3
• Frequent pulmonary function assessment with NIF and VC 1, 3
• Cardiac evaluation with ECG and echocardiogram if respiratory insufficiency or elevated cardiac markers to rule out concurrent myocarditis 3
• Monitor for complications of immunotherapy 3
• Minimum 24 hours monitoring even after apparent stabilization 3

Diagnostic Workup During Crisis

Confirm diagnosis and evaluate for complications:

• Acetylcholine receptor (AChR) antibodies and anti-striated muscle antibodies 3
• If AChR antibodies negative: test for MuSK and LRP4 antibodies 3
• CPK, aldolase, ESR, and CRP to evaluate for concurrent myositis 3

Expected Outcomes

Most patients improve within 1-2 weeks with appropriate treatment:

• Median duration of mechanical ventilation: 12-14 days 5
• Approximately 20% remain ventilated after 1 month, usually due to comorbidities 5
• Mortality rate in the United States is less than 5%, driven primarily by age and medical comorbidities rather than the crisis itself 4, 5, 8
• Long-term prognosis is generally favorable, with many patients achieving good MG control 4