What is the management approach for a myasthenic crisis?

Myasthenic Crisis Management

Myasthenic crisis requires immediate ICU admission with aggressive respiratory support, high-dose corticosteroids (methylprednisolone 1-2 mg/kg/day IV), and rapid immunotherapy with either plasmapheresis (5 sessions over 5 days) or IVIG (2 g/kg over 5 days), with plasmapheresis potentially superior for severe respiratory failure. 1

Immediate Stabilization and Monitoring

Secure the airway early through orotracheal intubation when respiratory compromise is evident—do not delay mechanical ventilation as this is the most critical intervention for survival. 2, 3

• Apply the "20/30/40 rule" to identify patients requiring intubation: vital capacity <20 ml/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O. 1
• Measure negative inspiratory force (NIF) and vital capacity (VC) immediately upon presentation and serially thereafter. 1
• Establish ICU-level monitoring with continuous pulse oximetry, cardiac monitoring, and frequent neurological assessments. 1
• Place wide-bore IV access and consider arterial line for blood gas monitoring. 1

A critical pitfall: Pulse oximetry and arterial blood gases may not detect early respiratory failure—rely on NIF/VC measurements and clinical assessment of work of breathing. 1

Acute Immunotherapy

Choose between plasmapheresis or IVIG as first-line rescue therapy:

• Plasmapheresis: 5 sessions over 5 days is the preferred option for severe respiratory failure based on evidence showing superior efficacy in crisis situations. 4, 3, 5
• IVIG: 2 g/kg total dose over 5 days (0.4 g/kg/day) is an alternative, though some patients may fail IVIG and subsequently respond to plasmapheresis. 1, 5

The median time to disease stabilization is 8 days with plasmapheresis versus 10 days with IVIG, though both are generally effective. 4 However, plasmapheresis appears superior when respiratory failure is already established. 3, 5

Corticosteroid Therapy

Initiate high-dose corticosteroids immediately:

• Methylprednisolone 1-2 mg/kg/day IV OR prednisone 1-1.5 mg/kg/day orally. 1
• Begin steroid taper 3-4 weeks after initiation based on clinical improvement. 1

Anticholinesterase Management

The role of pyridostigmine during crisis is controversial and limited. 3

• Many experts temporarily discontinue or reduce pyridostigmine during acute crisis to avoid confusing cholinergic crisis with myasthenic crisis. 6
• Cholinergic crisis warning: Overdosage of pyridostigmine causes increasing muscle weakness and respiratory muscle involvement that can be fatal—this is clinically indistinguishable from worsening myasthenic crisis. 6
• If cholinergic crisis is suspected, immediately withdraw all anticholinesterase drugs and consider atropine administration. 6

Medication Safety: Absolute Contraindications

Immediately discontinue these medications that can precipitate or worsen crisis:

• IV magnesium (absolutely contraindicated)—if severe hypomagnesemia requires treatment, mandatory neurology consultation before any administration. 1
• Beta-blockers of any kind. 7, 1
• Fluoroquinolone antibiotics. 7, 1
• Aminoglycoside antibiotics. 7, 1
• Macrolide antibiotics. 7, 1

Diagnostic Workup During Crisis

Obtain the following tests to guide management:

• Acetylcholine receptor (AChR) antibodies and anti-striated muscle antibodies. 1
• If AChR negative, test for MuSK and LRP4 antibodies. 1
• CPK, aldolase, ESR, CRP to evaluate for concurrent myositis. 1
• ECG and echocardiogram if elevated cardiac biomarkers to rule out myocarditis. 1
• Chest imaging and cultures to identify precipitating infection (present in 65% of cases). 4

Complications and Prognostic Factors

Ventilator-associated pneumonia (VAP) is the most common complication, occurring in 30% of cases. 4

Independent risk factors for prolonged mechanical ventilation include:

• Presence of thymoma (associated with 22-day average MV duration versus 9 days without thymoma). 8
• Elevated PCO₂ in blood gas before intubation. 8
• Development of pneumonia. 8

Median duration of mechanical ventilation is 12-14 days, with 20% still ventilated after 1 month. 2 Mortality ranges from 2-8% and is almost never from the crisis itself but from complications like VAP and sepsis. 4, 2

MuSK-antibody positive patients have significantly better outcomes with shorter MV duration (5 days versus 17 days), shorter ICU stays, and shorter hospitalizations compared to AChR-positive patients. 8

Long-term Immunosuppression

Initiate or optimize immunosuppression during crisis:

• Start azathioprine as steroid-sparing agent during hospitalization. 2
• Consider rituximab for refractory cases or as escalation therapy. 2

The lifetime risk of recurrent crisis is approximately 30%, with most crises occurring within the first 2 years of disease. 2