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
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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