#EMConf: Neuromuscular Disorders

Myasthenia Gravis

  • General: Autoimmune disease caused by antibodies to acetylcholine receptors in the neuromuscular junction
  • Clinical:
    • usually affects proximal muscles, neck extensors, facial/bulbar muscles (ptosis, diplopia, dysphagia, dysarthria)
    • usually no sensory or DTR deficit
    • associated with thymoma or thymic hyperplasia
    • Myasthenia Crisis: respiratory failure precipiated by infection vs. surgery vs. rapid taper in medication; may require intubation (be mindful of paralytic)
  • Diagnosis:
    • applying ice to ptosis (should improve)
    • administering edrophonium (anticholinesterase inhibitor) which should improve muscle weakness
    • acetylcholine receptor antibodies levels
    • EMG
  • Management:
    • assess respiratory function: VC < 1L; NIF < 20; weak cough; bulbar weakness
    • plasma exchange or IVIG
    • consult neurology and admit the patient to the ICU
    • acetylcholinesterase inhibitors (pyridostigmine, neostigmine)
    • thymectomy
    • immunosuppression with steroids and immunosuppressant
  • Medications that can exacerbate symptoms: fluoroquinolones, macrolides, aminoglycosides, paralytics, magnesium, penicillamine

Lambert-Eaton Syndrome

  • General: Autoimmune disorder caused by antibodies to voltage gated calcium channel in NMJ, preventing Acetylcholine release
  • Clinical:
      • affects proximal muscles, lower extremity more so than upper extremity
      • can have autonomic symptoms: dry mouth, constipation, erectile dysfunction
      • associated with small cell lung cancer
      • rarely results in respiratory or bulbar failure
  • Diagnosis: VGCC antibodies; repetitive nerve testing
  • Management:
    • 3,4-Diaminopyridine is first line
    • Steroids or IVIG
    • plasma exchange
    • search for underlying malignancy



Location of deficit




Ach receptors

Voltage gated calcium channels

Repeated muscle use

Worsens symptoms

Improves symptoms

Tumor association




Ach esterase inhibitors