What is the best course of treatment for a 66-year-old male in myasthenic crisis?

Management of Myasthenic Crisis in a 66-Year-Old Male

The best course of treatment for a 66-year-old male in myasthenic crisis requires immediate hospitalization with ICU-level monitoring, administration of corticosteroids, and initiation of either intravenous immunoglobulin (IVIG) or plasmapheresis to rapidly reduce antibody levels. 1

Initial Assessment and Management

• Immediately assess respiratory function with negative inspiratory force (NIF) and vital capacity (VC) measurements to determine severity of respiratory compromise 1
• Use the "20/30/40 rule" to identify respiratory failure risk: vital capacity <20 ml/kg, maximum inspiratory pressure <30 cmH₂O, or maximum expiratory pressure <40 cmH₂O 1
• Declare an emergency and call for help if respiratory parameters are concerning 2
• Establish good IV access with wide-bore cannulas for medication administration 2

Immediate Interventions

• Administer high-dose corticosteroids: methylprednisolone 1-2 mg/kg/day IV or consider pulse dosing (methylprednisolone 1 g/day for 5 days) in severe cases 1, 3
• Start one of the following rapid-acting immunotherapies:
  • Plasmapheresis (5 sessions over 5 days) OR
  • IVIG (2 g/kg total dose over 5 days at 0.4 g/kg/day) 1, 3
• Consider parenteral cholinesterase inhibitors if oral administration is not possible:
  • IV pyridostigmine (1 mg IV equals 30 mg oral) OR
  • IM neostigmine (0.75 mg IM equals 30 mg oral) when IV access is unavailable 3

Critical Monitoring

• Monitor respiratory function frequently, as respiratory failure is the defining feature of myasthenic crisis 1, 3
• Perform daily neurological evaluations to assess treatment response 1
• Check for bulbar symptoms (dysphagia, dysarthria, facial weakness) which may indicate impending respiratory compromise 3
• Obtain samples for diagnostic workup including:
  • Acetylcholine receptor (AChR) antibodies and anti-striated muscle antibodies 1
  • If AChR antibodies are negative, test for muscle-specific kinase (MuSK) and lipoprotein-related protein 4 (LRP4) antibodies 1
  • CPK, aldolase, ESR, and CRP to evaluate for concurrent myositis 1

Medications to AVOID

• IMMEDIATELY discontinue medications that can worsen myasthenia gravis:
  • Beta-blockers 1, 3
  • IV magnesium (absolutely contraindicated) 1, 3
  • Fluoroquinolones 1, 3
  • Aminoglycosides 1, 3
  • Macrolide antibiotics 1, 3, 4

Treatment Efficacy and Complications

• Both plasmapheresis and IVIG are equally effective in disease stabilization, with time to extubation ranging from 7-12 days for PE and 7-39 days for IVIG 5
• Ventilator-associated pneumonia (VAP) is the most common complication, occurring in approximately 30% of cases 5
• Thymoma, elevated PCO2 before mechanical ventilation, and pneumonia are independent risk factors for prolonged mechanical ventilation 6
• MuSK-associated myasthenic crisis may have shorter duration of mechanical ventilation compared to AChR antibody-positive cases 6

Prognosis and Follow-up

• With appropriate management, mortality rates in myasthenic crisis have decreased significantly to approximately 2-8% 5, 6
• Begin steroid taper 3-4 weeks after initiation, based on symptom improvement 1
• Monitor for cardiac arrhythmias, as they can occur in up to 17% of myasthenic crisis cases and may be fatal 7
• Regular follow-up with neurology is essential to adjust treatment as needed 4

Common Pitfalls to Avoid

• Delaying intubation and mechanical ventilation in patients with declining respiratory parameters 8
• Failing to identify and treat infections, which are the most common precipitants of myasthenic crisis (occurring in up to 65% of cases) 5
• Using medications that can worsen myasthenia gravis symptoms 1, 3, 4
• Inadequate monitoring for complications such as ventilator-associated pneumonia and cardiac arrhythmias 5, 7