What is the management of a myasthenia crisis?

Management of Myasthenia Crisis

The management of myasthenia crisis requires immediate respiratory support, discontinuation of triggering factors, and rapid immunomodulatory therapy with plasmapheresis as the preferred first-line treatment due to its faster onset of action compared to IVIG. 1, 2

Definition and Recognition

Myasthenia crisis is a life-threatening manifestation of myasthenia gravis characterized by:

• Respiratory insufficiency requiring invasive or non-invasive ventilation
• Often preceded by worsening bulbar or generalized weakness
• May be triggered by infections (most common), medications, surgery, or stress
• Occurs in 15-20% of MG patients, usually within the first 2-3 years of diagnosis 2

Initial Management

1. Airway and Respiratory Support

   • Maintain low threshold for intubation if respiratory parameters deteriorate
   • Monitor negative inspiratory force (NIF) and vital capacity (VC) closely
   • Admit to hospital with ICU capability 1

2. Differentiate Myasthenic vs. Cholinergic Crisis

   • Myasthenic crisis: Worsening disease requiring increased anticholinesterase therapy
   • Cholinergic crisis: Overdose of anticholinesterase medications requiring withdrawal of these drugs
   • May require edrophonium chloride test for differentiation 3
   • Misdiagnosis can lead to grave consequences with inappropriate medication adjustments 3

3. Remove Potential Triggers

   • Discontinue medications that can exacerbate MG: aminoglycosides, fluoroquinolones, macrolides, β-blockers, IV magnesium, daptomycin 1
   • Treat underlying infections with safer alternatives: penicillins, cephalosporins, tetracyclines 1
   • For MRSA infections, consider linezolid (with monitoring) or vancomycin 1

Immunomodulatory Treatment

1. First-Line Rapid Therapy

   • Plasmapheresis (preferred):

     • 5 treatment sessions
     • Works through direct antibody removal
     • Associated with reduced ICU stay length and earlier clinical response 4
     • Particularly effective for rapid improvement in respiratory compromise 1

   • Intravenous Immunoglobulin (IVIG):

     • 2 g/kg divided over 5 days (400 mg/kg/day for 5 days)
     • Alternative when plasmapheresis is unavailable or contraindicated
     • Equally effective as plasmapheresis after 1 month, but slower initial response 4

2. Concurrent Immunosuppressive Therapy

   • Corticosteroids: Prednisone 1-1.5 mg/kg PO daily 1
   • Continue previous immunosuppressants if already on them

Monitoring and Supportive Care

• Frequent neurological assessments and pulmonary function monitoring
• Monitor for autonomic dysfunction
• Obtain neurology consultation
• Provide DVT prophylaxis, nutritional support, and prevention of complications
• Adjust pyridostigmine dosing based on response:
  • May need to temporarily reduce or discontinue if cholinergic crisis is suspected
  • Atropine can be used to manage cholinergic side effects 3

Follow-up Management

• Once stabilized, maintenance therapy may include:
  • Pyridostigmine: Starting at 30 mg orally three times daily, titrating up to maximum of 120 mg four times daily 1
  • Corticosteroids: Prednisone 0.5-1.5 mg/kg daily 1
  • Consider maintenance IVIG (400 mg/kg monthly) in refractory cases 5, 6
  • Evaluate for thymectomy if indicated (all thymoma cases, non-thymomatous MG under 55-60 years) 1

Prognosis

• Most patients can be weaned from mechanical ventilation within 1 month
• Mortality rate is less than 5% in US cohorts, primarily driven by age and medical comorbidities
• Myasthenic crisis does not appear to affect long-term prognosis 2

Common Pitfalls to Avoid

1. Failure to differentiate between myasthenic and cholinergic crisis

   • Incorrect management can worsen the patient's condition
   • Use clinical judgment and possibly edrophonium testing for differentiation 3

2. Inappropriate medication use

   • Avoid medications known to exacerbate MG
   • Be cautious with anticholinesterase dosing, as overdosage can precipitate cholinergic crisis 3

3. Delayed respiratory support

   • Maintain low threshold for intubation rather than waiting for complete respiratory failure
   • Regular monitoring of respiratory parameters is essential 1

4. Overlooking precipitating factors

   • Identify and treat underlying infections or other triggers
   • Review all medications for potential MG exacerbation 1