What is the specific treatment for myasthenic crisis?

Specific Treatment for Myasthenic Crisis

Myasthenic crisis requires immediate ICU admission with aggressive immunotherapy using either intravenous immunoglobulin (IVIG) 2 g/kg over 5 days (0.4 g/kg/day) or plasmapheresis (5 sessions over 5 days), combined with high-dose corticosteroids and discontinuation of pyridostigmine until respiratory stabilization occurs. 1, 2

Immediate Management Steps

Airway and Respiratory Support

• Admit to ICU immediately for continuous respiratory monitoring with frequent pulmonary function assessments measuring negative inspiratory force (NIF) and vital capacity (VC) 1, 2
• Apply the "20/30/40 rule" to identify impending respiratory failure: vital capacity <20 ml/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O 1
• Intubate and mechanically ventilate if respiratory failure develops; noninvasive ventilation can be attempted first in select cases 3
• The median duration of mechanical ventilation is approximately 8-11 days with appropriate therapy 4

Immunotherapy (Choose One)

Both options are equally effective for disease stabilization 4:

• IVIG: 2 g/kg total dose administered as 0.4 g/kg/day for 5 consecutive days 1, 2, 4
• Plasmapheresis: 5 sessions over 5 days 1, 4

The time to disease stabilization is similar between both therapies (8 days for plasmapheresis vs 10 days for IVIG) 4

Corticosteroid Therapy

• Administer methylprednisolone 1-2 mg/kg/day IV or prednisone 1-1.5 mg/kg/day orally 1
• Steroid dosage can be increased once the airway is secured 3
• Begin tapering 3-4 weeks after initiation based on symptom improvement 1, 2

Pyridostigmine Management

• Discontinue pyridostigmine during the acute crisis to avoid cholinergic crisis and because it is ineffective during severe weakness 3, 5
• Resume pyridostigmine prior to extubation, starting at 30 mg orally three times daily and titrating to maximum 120 mg four times daily 3, 2

Critical Medication Precautions

Immediately discontinue these medications that worsen myasthenia gravis 1, 2, 6:

• Beta-blockers
• IV magnesium (absolutely contraindicated)
• Fluoroquinolone antibiotics
• Aminoglycoside antibiotics
• Macrolide antibiotics

Essential Diagnostic Workup

• Measure acetylcholine receptor (AChR) antibodies and anti-striated muscle antibodies 1, 2
• If AChR antibodies are negative, test for muscle-specific kinase (MuSK) and lipoprotein-related protein 4 (LRP4) antibodies 1, 2
• Check CPK, aldolase, ESR, and CRP to evaluate for concurrent myositis 1, 2
• Perform ECG and troponin; consider transthoracic echocardiogram to rule out concurrent myocarditis 1, 2

Monitoring Requirements

• Daily neurological evaluation 1, 2
• Frequent pulmonary function assessment with NIF and VC measurements 1, 2
• Establish wide-bore IV access; consider arterial line, central venous line, and urinary catheter 2
• Monitor electrolytes (K+), arterial blood gases, myoglobin, glucose, renal and hepatic function, and coagulation 2
• Minimum 24-hour monitoring in ICU/HDU setting 2

Management of Complications

Ventilator-Associated Pneumonia

• This is the most common complication, occurring in approximately 30% of cases 4
• Aggressive treatment of infections is essential, as infection is the most common precipitant of crisis (65% of cases) 4

Thymoma-Associated Considerations

• Patients with thymoma-associated myasthenia gravis have significantly longer mechanical ventilation duration (22 days vs 9 days) and hospital stays compared to non-thymoma patients 7
• Thymoma is an independent risk factor for prolonged mechanical ventilation (OR: 0.200) 7

Alternative Therapy for Resource-Limited Settings

• If IVIG or plasmapheresis is unavailable, continuous intravenous infusion of pyridostigmine or neostigmine can be used as a substitute, though this carries risk of cardiac arrhythmia and pneumonia 8
• This approach should only be considered when standard immunotherapy is genuinely unavailable 8

Refractory Cases

• For patients unresponsive to IVIG or plasmapheresis, consider adding rituximab 2
• Eculizumab (complement inhibitor) shows promise as rescue therapy in refractory myasthenic crisis with complete resolution reported within 5 days, though this remains investigational 9

Expected Outcomes

• With timely rescue therapies and ICU management, in-hospital mortality is approximately 2-8% 7, 4
• Complete resolution of admission symptoms occurs in the vast majority of survivors 4
• MuSK-antibody positive patients have significantly shorter mechanical ventilation duration (5 days vs 17 days), ICU stay, and hospital stay compared to AChR-positive patients 7