How do you differentiate a cholinergic crisis from a myasthenia crisis?

Differentiating Cholinergic Crisis from Myasthenia Crisis

Perform a Tensilon (edrophonium) test is the best approach to differentiate a cholinergic crisis from a myasthenia crisis. 1

Rationale for Using Tensilon Test

The Tensilon test is specifically designed to distinguish between these two critical conditions:

• In myasthenic crisis (undertreated myasthenia gravis): Administration of edrophonium will temporarily improve muscle strength
• In cholinergic crisis (overdose of anticholinesterase medications): Administration of edrophonium will worsen symptoms and may increase respiratory distress 2, 1

Proper Administration of Tensilon Test

1. Preparation and Safety Measures:

   • Prepare a tuberculin syringe with 1 mL (10 mg) of edrophonium
   • Have atropine (0.4-0.5 mg) immediately available to reverse cholinergic effects if needed
   • Perform in a monitored setting with resuscitation equipment 1
   • Continuous cardiac monitoring is essential

2. Administration Protocol:

   • Initial test dose: 0.2 mL (2 mg) IV over 15-30 seconds
   • Wait 45 seconds to observe response
   • If no reaction occurs, administer remaining 0.8 mL (8 mg)
   • If cholinergic reaction occurs after initial dose, discontinue test and administer atropine 1

3. Interpretation of Results:

   • Myasthenic crisis: Improvement in muscle strength without significant muscarinic side effects
   • Cholinergic crisis: Worsening weakness and increased muscarinic symptoms (increased secretions, abdominal cramps, diarrhea) 2, 1

Alternative Diagnostic Approaches

While Tensilon testing is the gold standard, other methods can be considered when edrophonium is unavailable or contraindicated:

• Ice pack test: Application over closed eyes for 2-5 minutes may temporarily improve ptosis and ocular misalignment in myasthenia gravis 3, 2
• Rest test: Observation for improvement after a period of rest can help diagnose myasthenia gravis 4
• Clinical features differentiation:
  • Cholinergic crisis: Presents with muscarinic symptoms (excessive secretions, lacrimation, diarrhea, bradycardia) alongside weakness 5, 6
  • Myasthenic crisis: Primarily presents with worsening weakness without prominent muscarinic symptoms 7

Critical Management Considerations

• In respiratory distress, secure the airway first before diagnostic testing
• When a patient is apneic, controlled ventilation must be secured immediately before attempting the Tensilon test 1
• For crisis testing, use smaller doses (0.1 mL/1 mg initially) with careful cardiac monitoring 1
• If no clear improvement occurs after 0.2 mL (2 mg), discontinue anticholinesterase therapy and secure airway with assisted ventilation 1

Cautions and Contraindications

• Tensilon testing carries risks including bradycardia, bronchospasm, and hypotension
• The test should be performed by practitioners experienced with proper administration 3
• Avoid testing in patients with cardiac conditions that may be exacerbated by cholinergic effects
• In severe respiratory compromise, securing the airway takes precedence over diagnostic testing 7

The Tensilon test remains the most definitive method to differentiate between these two life-threatening conditions, allowing for appropriate management decisions that directly impact mortality and morbidity.