Myasthenia gravis: Difference between revisions

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**Thymectomy resolves or improves symptoms in most pts, especially those with a thymoma
**Thymectomy resolves or improves symptoms in most pts, especially those with a thymoma
*No sensory, reflex, or cerebellar deficits
*No sensory, reflex, or cerebellar deficits
*Respiratory failure is feared complication
**Often precipitated by infection, surgery, or rapid tapering of immunosuppressive drugs


===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


==Clinical Features==
==Clinical Features==
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==DDX==
==DDX==
#Cholinergic crisis
#Lambert-Eaton Syndrome
#Lambert-Eaton Syndrome
#Drug-induced myasthenia (penicillamine, procainamide, quines, aminoglycosides)
#Botulism
#Botulism
#Thyroid disorders
#Thyroid disorders
#Drug-induced myasthenia
##Abx (aminoglycosides, flouroquinolones, clindamycin, metronidazole, macrolides)
##Steroids
##Anticonvulsants (phenytoin, barbiturates, lithium)
##Psychotropics (haloperidol)
##Beta-blockers / calcium-channel blockers
##Local anesthetics
##Narcotics
##Anticholinergics (diphenhydramine)
##NMJ blocking agents (roc, sux)


==Management==
==Treatment==
*Always evaluate tidal volume, FEV, ability to handle secretions
*Always evaluate tidal volume, FEV, ability to handle secretions
#Meds
#Meds
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##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  
 
#Plasmapherisis
 
#IVIG
 
===Testing===
# Always test FEV, consider ABG, Look for infections (resp) or meds, electrolyte problems that may have induced problem.
# Edrophonium - use caution in trying to test for crisis vs. cholinergic crisis
# Ach receptor antibodies - found 90%
# CT of thymus, TFTs, search for other immun dz
 
==Treatment==
# Plasmapherisis or plasma exchenge in acute setting
# Anticholinesterase agent such as Pyridostigmine 60 mg tid
# Corticosteroids produce good results in >80% but are reserved for those who don't respond to anti-cholinesterases and thymectomy due to adverse effects. Decreases levels of antiAch receptor Ab. Also may initially aggravate muscle weakness so usually begun in hosp & at low doses
 
#don't treat Myasthenic with meds that may exacerbate weakness
# search for source of infection or electrolyte problem w/ weakness
 
===Myasthenic Crisis vs. Cholinergic===
# Cholinergic - usually present w/ signs of cholinergic overactivity (miosis, sweats, salivation, GI distress-musc) & cramps, fasciculations (nicotinic)
# Myasthenic - more common, caused by noncompliance, drug interaction, infection, stress
## aminoglycosides, flouroquinolones, clinda, sulfas, erythro, ampicillin, Dilantin, phenobarb, B blockers, Ca channel Blk, procainamide, steroids, lithium, phenothiazines, MSO4, benzos, antihistamines
 
VERY DANGEROUS & UNRELIABLE to use Tensilon Test to distinguish between the two.


==Source==
==Source==
Harwood Nuss p.1002
*Tintinalli


[[Category:Neuro]]
[[Category:Neuro]]

Revision as of 05:51, 6 October 2011

Background

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

Myasthenic Crisis versus Cholinergic Crisis

  1. Myasthenic Crisis
    1. Respiratory failure is feared complication
    2. Much more common
    3. D/t med non-compliance, infection, surgery, tapering of immunosuppressants, meds
  2. Cholinergic Crisis
    1. Excessive anticholinesterase medication may cause weakness and cholinergic symptoms
    2. Rarely if ever seen w/ dose limitation of pyridostigmine to less than 120mg q3hr
    3. If on usual dose of meds assume exacerbation due to MG even w/ cholinergic side effects
  3. Edrophonium (Tensilon) test to distinguish the two is controversial

Clinical Features

  1. Symptoms worsen with repetitive use / as the day progresses
  2. Muscle weakness
    1. Proximal extremities
    2. Neck extensors
    3. Facial/bulbar muscles (dysphagia, dysarthria, dysphonia)
  3. Ocular weakness
    1. Ptosis
    2. Diplopia
    3. CN III, IV, or VI weakness

DDX

  1. Cholinergic crisis
  2. Lambert-Eaton Syndrome
  3. Botulism
  4. Thyroid disorders
  5. Drug-induced myasthenia
    1. Abx (aminoglycosides, flouroquinolones, clindamycin, metronidazole, macrolides)
    2. Steroids
    3. Anticonvulsants (phenytoin, barbiturates, lithium)
    4. Psychotropics (haloperidol)
    5. Beta-blockers / calcium-channel blockers
    6. Local anesthetics
    7. Narcotics
    8. Anticholinergics (diphenhydramine)
    9. NMJ blocking agents (roc, sux)

Treatment

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

Source

  • Tintinalli
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