What is the recommended acute management for a patient experiencing a myasthenic crisis, including airway protection, ventilation support, plasma exchange or intravenous immune globulin, corticosteroid therapy, and medication adjustments?

Myasthenic Crisis Management

Immediately secure the airway with early intubation, initiate plasma exchange as first-line immunotherapy, and discontinue cholinesterase inhibitors during the acute phase.

Immediate Airway Management and Respiratory Support

Early intubation is the single most critical intervention in myasthenic crisis and should be performed semi-electively before respiratory arrest occurs. 1, 2 The orotracheal approach is preferred for intubation, with placement of small-bore duodenal feeding tubes to decrease aspiration risk and improve patient comfort compared to standard nasogastric tubes. 2

• Intubate when forced vital capacity (FVC) falls below 15–20 mL/kg, negative inspiratory force (NIF) is less negative than –30 cm H₂O, or when bulbar weakness causes aspiration or upper airway collapse. 1, 3
• Do not delay intubation waiting for "maximal medical therapy"—the rapidly progressive weakness of respiratory and bulbar muscles can lead to sudden decompensation within minutes to days. 1
• Median duration of mechanical ventilation is 12–14 days under appropriate treatment, though 20% of patients remain ventilated beyond 1 month due to complications. 1

First-Line Immunotherapy: Plasma Exchange Over IVIG

Plasma exchange is superior to intravenous immunoglobulin for myasthenic crisis and should be initiated immediately. 2, 4, 5 In a prospective cohort of anti-AChR antibody-positive myasthenic crisis patients, plasma exchange reduced ICU stay length (p=0.018) and produced earlier clinical response by one week off-ventilation compared to IVIG. 4

• Administer 5 exchanges over 7–10 days (typically 1–1.5 plasma volumes per exchange). 2, 4
• Plasma exchange produces faster improvement in MGFA-QMG scores (p=0.003), manual muscle testing (p=0.020), and activities of daily living (p=0.011) at one week compared to IVIG. 4
• IVIG (2 g/kg divided over 2–5 days, typically 0.4 g/kg/day) is an acceptable alternative when plasma exchange is contraindicated or unavailable, though it may be less effective in respiratory failure. 2, 3
• Four patients who failed IVIG subsequently responded to intensive plasma exchange, suggesting plasmapheresis should be attempted when IVIG fails. 5

Medication Adjustments During Crisis

Discontinue pyridostigmine and other cholinesterase inhibitors during the acute phase of myasthenic crisis. 1, 2 The role of intravenous or intramuscular pyridostigmine in the acute setting remains limited and controversial, with therapy tailored on an individual basis using clinical judgment. 2

• Review and stop medications that worsen myasthenia: beta-blockers, IV magnesium, fluoroquinolones, aminoglycosides, and macrolide antibiotics. 6
• Initiate or optimize immunosuppression with corticosteroids (prednisone 0.5–1 mg/kg daily) and azathioprine once the patient is stabilized. 1
• For refractory cases, consider rituximab as escalation therapy. 6, 1

Corticosteroid Timing and Dosing

Administer corticosteroids (prednisone 0.5 mg/kg orally daily) after plasma exchange or IVIG has been initiated, not before, to avoid initial worsening. 6 Begin steroid taper 3–4 weeks after initiation based on symptom improvement. 6

Monitoring and Supportive Care

• Perform frequent pulmonary function assessment with NIF and vital capacity measurements to guide extubation readiness. 6, 1
• Obtain daily neurologic review and continuous monitoring in the ICU setting. 6
• Aggressively diagnose and treat infections and other complications (delirium, aspiration pneumonia) as these drive mortality more than the crisis itself. 1, 3
• Check AChR and antistriated muscle antibodies; if AChR antibodies are negative, consider MuSK and LRP4 antibodies, though absence does not rule out myasthenia. 6

Critical Pitfalls to Avoid

• Do not wait for respiratory arrest before intubating—early semi-elective intubation prevents catastrophic decompensation. 1, 2
• Do not continue cholinesterase inhibitors during crisis—they provide minimal benefit and may complicate management. 1, 2
• Do not use IVIG as first-line when plasma exchange is available—plasma exchange is more effective for respiratory failure. 2, 4, 5
• Do not start high-dose corticosteroids before plasma exchange/IVIG—this can precipitate acute worsening. 6

Prognosis and Risk Factors

Myasthenic crisis occurs in 15–20% of MG patients, most commonly within the first 2–3 years of disease or as the initial manifestation in up to 20% of cases. 1, 3 Mortality in U.S. cohorts is less than 5% and is driven by age and medical comorbidities rather than the crisis itself. 3 The lifetime risk of recurrent crisis is approximately 30%. 1 Patients with MuSK antibodies, thymoma, severe disease, oropharyngeal weakness, or prior crisis history are at higher risk. 3