MYASTHENIA GRAVIS/LAMBERT EATON (MG/LEMS): 
Weakness ...
272
Description

MYASTHENIA GRAVIS/LAMBERT EATON (MG/LEMS): 

Weakness of voluntary muscles, worse w/ exertion & repetitive movements and in the evening. Typically involves ocular (ptosis, diplopia), bulbar, respiratory, neck and proximal>distal limb muscles.

 • Cause: Auto-Abs against postsynaptic ACh-R in skeletal muscle (MG) or Voltage Gated Calcium Channels (LEMS)

 • Exam: Upgaze fatiguability – hold sustained upgaze for 1 min, look for development of ptosis. After 

 observing ptosis, place ice on eyes for 1 min, weakness will improve (Tensilon test rare, requires atropine at the bedside. Only improves MG not LEMS).

 • Dx: Ach-R Ab (80-90% seropositive, specific); if neg check anti-MUSK. EMG/NCS: Order w/repetitive stim; will show decremental response (MG) or potentiation (LEMS). Chest CT I+: r/o thymoma (in 70-80% MG). Find underlying malignancy in LEMS.

 • Tx: Symptomatic (pyridostigmine); immunotherapy: rapid (IVIg, plasmapheresis), chronic (steroids+/ azathioprine/MMF); thymectomy 

MYASTHENIC CRISIS: 

MG exacerbation requiring intubation or delayed extubation post-surgery

 • Triggers: surgery, infection, IV contrast, pregnancy, certain drugs/meds (antibiotics including fluoroquinolones, aminoglycosides; anticonvulsants; antipsychotics; BBs; CCBs; mag). AVOID succinylcholine during intubation.

 • Respiratory failure: bedside exam → follow number counting in single breath, assess cough/swallowing. Trend mechanics with RT: NIFs/VC as above (see 20-30-40 Rule). Aggressive pulm toilet. HOLD pyridostigmine if bulbar sx and/or intubated (can ↑ secretions).



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