Skip to content

Myasthenia Gravis (MG) and Lambert-Eaton Myasthenic Syndrome (LEMS)


  • Disorders of the neuromuscular junction

  • MG affects the post-synaptic cleft at the acetylcholine receptor

  • LEMS affects the pre-synaptic cleft at the calcium channels

    • Many cases are paraneoplastic (classically small cell lung carcinoma)


  • Double vision, ptosis, dysarthria, dysphagia

  • Dyspnea looks different than in other conditions: air hunger, usually also with dysphagia

  • Initially, the patient may not look sick or distressed, but may have a short inspiratory time or difficulty speaking in complete sentences due to shallow breathing

  • Most pts have a known history of myasthenia, but up to 20% present initially with crisis


  • Exam

    • Look closely for ptosis, nasal speech, weak neck flexion/extension (same nerve roots as diaphragm), interrupted speech to take extra breaths

    • These patients do not exhibit “huffing and puffing” like in COPD/asthma exacerbations

      • Patients with NMJ disease can go from talking to intubated within several hours!
    • LEMS: less ocular weakness, but do have extremity weakness and absent reflexes.

    • Pulmonary compromise is very rare in LEMS


    • MG: decremental response to repetitive stimulation

    • LEMS: increased amplitude in response to repetitive stimulation

  • Labs

    • Myasthenia antibody panels (send prior to IVIG/PLEX being given)
  • Imaging

    • Consider chest CT to look for thymic hyperplasia


  • Monitor NIF (negative inspiratory force) at baseline and q4h

    • Measure of diaphragmatic strength

    • Normal is \<-60

    • If below -30, consider elective intubation

    • Note that patient effort will affect NIF values

  • IVIG or PLEX

    • Both have similar supportive evidence; IVIG is usually easier to do

    • PLEX has the risks you would expect with dialysis (e.g. fluid shifts) and coagulopathy

    • IVIG -> check IgA levels. Can increase risk of DVT, has risk of aseptic meningitis and provides significant fluid load so not ideal for pts with CHF

  • Steroids

    • Usually up-titrated SLOWLY (by 10-20 mg prednisone daily)

    • Rapid increases in steroids can worsen patients with MG**, so talk to neuro before adjusting**

  • Pyridostigmine

    • Typically continue at their home dose

    • Too much pyridostigmine can make patients worse (more secretions), so for those doing poorly on >90 mg per dose, consider lowering the dose

  • Treat underlying causes of exacerbations: usually infections or other toxic/metabolic insults

  • Remove/avoid exacerbating medications: fluoroquinolones, aminoglycosides, beta blockers, and magnesium

  • LEMS specific management:

    • 3,4-diaminopyridine

    • Can respond to IVIG or pyridostigmine

    • Workup for underlying neoplasm

Last update: 2022-06-23 16:46:27