Myasthenia gravis: Difference between revisions

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===Myasthenic Crisis versus Cholinergic Crisis===
===Myasthenic Crisis versus Cholinergic Crisis===
#Myasthenic Crisis
*Myasthenic Crisis
##Respiratory failure is feared complication
**Respiratory failure is feared complication
##Much more common
**Much more common
##D/t med non-compliance, infection, surgery, tapering of immunosuppressants, meds
**D/t med non-compliance, infection, surgery, tapering of immunosuppressants, meds
#Cholinergic Crisis
*Cholinergic Crisis
##Excessive anticholinesterase medication may cause weakness and cholinergic symptoms
**Excessive anticholinesterase medication may cause weakness and cholinergic symptoms
##Rarely if ever seen w/ dose limitation of pyridostigmine to less than 120mg q3hr
**Rarely if ever seen w/ dose limitation of pyridostigmine to less than 120mg q3hr
##If on usual dose of meds assume exacerbation due to MG even w/ cholinergic side effects
**If on usual dose of meds assume exacerbation due to MG even w/ cholinergic side effects
#Edrophonium (Tensilon) test to distinguish the two is controversial
*Edrophonium (Tensilon) test to distinguish the two is controversial
##Give 1-2 mg IV slow push. If any fasciculations, resp depression, or cholinergic symptoms within a few minutes, problem is likely cholinergic crisis (no more edrophonium). If no evidence of cholinergic excess, give total of 10 mg and observe improvement in case of myasthenic crisis.
**Give 1-2 mg IV slow push. If any fasciculations, resp depression, or cholinergic symptoms within a few minutes, problem is likely cholinergic crisis (no more edrophonium). If no evidence of cholinergic excess, give total of 10 mg and observe improvement in case of myasthenic crisis.
## Side effects of Edrophonium: Arrhythmias, Hypotension, Bronchospasm
** Side effects of Edrophonium: Arrhythmias, Hypotension, Bronchospasm
## Treatment: Atropine
** Treatment: Atropine


==Clinical Features==
==Clinical Features==
#Symptoms worsen with repetitive use / as the day progresses<ref>Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7e (2010), Chapter 167. Chronic Neurologic Disorders</ref>
*Symptoms worsen with repetitive use / as the day progresses<ref>Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7e (2010), Chapter 167. Chronic Neurologic Disorders</ref>
##Ice Pack Test- should improve symptoms temporarily (usually ptosis; high specificity)
**Ice Pack Test- should improve symptoms temporarily (usually ptosis; high specificity)
###Place ice-pack on eyes for 2 mins, if ptosis decreases by ≥2mm the test is positive
***Place ice-pack on eyes for 2 mins, if ptosis decreases by ≥2mm the test is positive
#Muscle weakness
*Muscle weakness
##Proximal extremities
**Proximal extremities
##Neck extensors
**Neck extensors
##Facial/bulbar muscles (dysphagia, dysarthria, dysphonia)
**Facial/bulbar muscles (dysphagia, dysarthria, dysphonia)
#Ocular weakness
*Ocular weakness
##Ptosis
**Ptosis
##[[Diplopia]]
**[[Diplopia]]
##CN III, IV, or VI weakness
**CN III, IV, or VI weakness


==Differential Diagnosis==
==Differential Diagnosis==
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==Treatment==
==Treatment==
*Always evaluate tidal volume, FEV, negative inspiratory force, ability to handle secretions
*Always evaluate tidal volume, FEV, negative inspiratory force, ability to handle secretions
#Meds
*Meds
##Pyridostigmine
**Pyridostigmine
###If pt's usual dose has been missed the next dose is usually doubled
***If pt's usual dose has been missed the next dose is usually doubled
###PO route: 60-90mg q4hr
***PO route: 60-90mg q4hr
###IV route: 1/30th of the PO dose (2-3mg) by slow IV infusion
***IV route: 1/30th of the PO dose (2-3mg) by slow IV infusion
##Neostigmine
**Neostigmine
###0.5mg IV
***0.5mg IV
#[[Intubation]]
*[[Intubation]]
##If possible avoid depolarizing AND non-depolarizing agents
**If possible avoid depolarizing AND non-depolarizing agents
###If pt requires paralysis use non-depolarizing agent at smaller dose  
***If pt requires paralysis use non-depolarizing agent at smaller dose  
###If must use depolarizing agents, will need higher doses
***If must use depolarizing agents, will need higher doses
#Plasmapherisis
*Plasmapherisis
#IVIG
*IVIG


==See Also==
==See Also==

Revision as of 23:49, 19 July 2015

Background

  • Autoantibody degradation, dysfunction, and blockade of acetylcholine receptor at the NMJ[1]
  • Thymus is abnormal in 75% of pts
    • Thymectomy resolves or improves symptoms in most pts, especially those with a thymoma
  • No sensory, reflex, pupillary, or cerebellar deficits

Myasthenic Crisis versus Cholinergic Crisis

  • Myasthenic Crisis
    • Respiratory failure is feared complication
    • Much more common
    • D/t med non-compliance, infection, surgery, tapering of immunosuppressants, meds
  • Cholinergic Crisis
    • Excessive anticholinesterase medication may cause weakness and cholinergic symptoms
    • Rarely if ever seen w/ dose limitation of pyridostigmine to less than 120mg q3hr
    • If on usual dose of meds assume exacerbation due to MG even w/ cholinergic side effects
  • Edrophonium (Tensilon) test to distinguish the two is controversial
    • Give 1-2 mg IV slow push. If any fasciculations, resp depression, or cholinergic symptoms within a few minutes, problem is likely cholinergic crisis (no more edrophonium). If no evidence of cholinergic excess, give total of 10 mg and observe improvement in case of myasthenic crisis.
    • Side effects of Edrophonium: Arrhythmias, Hypotension, Bronchospasm
    • Treatment: Atropine

Clinical Features

  • Symptoms worsen with repetitive use / as the day progresses[2]
    • Ice Pack Test- should improve symptoms temporarily (usually ptosis; high specificity)
      • Place ice-pack on eyes for 2 mins, if ptosis decreases by ≥2mm the test is positive
  • Muscle weakness
    • Proximal extremities
    • Neck extensors
    • Facial/bulbar muscles (dysphagia, dysarthria, dysphonia)
  • Ocular weakness
    • Ptosis
    • Diplopia
    • CN III, IV, or VI weakness

Differential Diagnosis

Drug-induced myasthenia

Weakness

Treatment

  • Always evaluate tidal volume, FEV, negative inspiratory force, ability to handle secretions
  • Meds
    • Pyridostigmine
      • If pt's usual dose has been missed the next dose is usually doubled
      • PO route: 60-90mg q4hr
      • IV route: 1/30th of the PO dose (2-3mg) by slow IV infusion
    • Neostigmine
      • 0.5mg IV
  • Intubation
    • If possible avoid depolarizing AND non-depolarizing agents
      • If pt requires paralysis use non-depolarizing agent at smaller dose
      • If must use depolarizing agents, will need higher doses
  • Plasmapherisis
  • IVIG

See Also

Source

  1. ↑ Medications and Myasthenia Gravis (A Reference for Health Care Professionals) PDF
  2. ↑ Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7e (2010), Chapter 167. Chronic Neurologic Disorders
  3. ↑ Sanders DB, Guptill JT. Myasthenia Gravis and Lambert-Eaton Myasthenic Syndrome. Continuum. 2014 Oct;20(5)
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