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• Myasthenia gravis


  Autoimmune disorder of neuromuscular junction (type II hypersensitivity)
• Myasthenia gravis


  • Anti-acetylcholine receptor antibodies at the postsynaptic membrane of NMJ
  • Can present at any age, peaks in the third (females) and sixth (males) decade, more in women
  • Associated with thymic hyperplasia (70%), thymoma (10%) or other autoimmune disorders ex: thyroid, rheumatoid, and pernicious anemia (must screen)
• Clinical manifestations of condition


  • Weakness and fatigability of ocular, bulbar, and proximal limb weakness
  • Weakness is descending (starts from the top and moves down)
  • Muscle fatigue after sustained/repetitive action, better with rest
  • Ocular muscles - ptosis and diplopia, better with sleep/icepack
  • Difficulty swallowing, chewing, and talking (nasal speech)
  • Respiratory difficulties
  • Diurnal variation (symptoms worse at night)
• Bedside tests


  1. Worse when counting to 20 quickly

  2. Upward gaze - ptosis; relieved by icepacks

  3. Outstretched arms - slow downward drift
• Normal reflexes
• Anti-AChR antibodies


  • Most specific
• Single fiber electromyography


  • Most sensitive
• Nerve stimulation test


  Decrement in evoked potential
• Anti-MuSK antibodies


  Seronegative disease; mostly ocular manifestations
• CT


  • Thymoma/thymic hyperplasia
• Tensilon test


  1. Giving IV anticholinesterase

  2. Temporary rapid improvement
• Differential diagnosis of MG


  • Thyroid ophthalmopathy
  • Myotonic dystrophy
  • Brainstem cranial nerve lesions
  • Motor neuron disease
  • Lambert-Eaton myasthenic syndrome
• Lambert-Eaton myasthenic syndrome


  • Associated with small cell lung cancer
  • Autoantibodies against presynaptic calcium channels
  • Presents with proximal muscle weakness and hyporeflexia
  • Symptoms improve with repeated muscle stimulation
• Botulism


  • History of consumption of contaminated food (clostridium botulinum: anaerobic spore forming bacteria→neurotoxin production)
  • Acute onset of bilateral cranial neuropathies, pupillary paralysis, hyporeflexia, symmetrical descending weakness, anticholinergic symptoms
• Anticholinesterases (pyridostigmine)


  ↑ availability of Ach at NMJ
• Immunosuppressants


  • steroids
  • azathioprine
• If no response/relapse on Tx

  Use immunosuppressants
• Thymectomy


  • Indicated if thymoma is seen on CT (malignant potential)
  • Indicated if no thymoma but <50 years old & anti AchR antibodies +ve
• Acute Myasthenic Crisis


  • Life-threatening condition
  • Profound weakness
  • Respiratory/bulbar involvement
• Triggers for Acute Myasthenic Crisis


  • Drugs (aminoglycosides, macrolides, fluoroquinolones, phenytoin, BBs)
  • Upper respiratory tract infection
  • Surgery
  • Pregnancy/postpartum
• Treatment for Acute Myasthenic Crisis

  1. Plasmapheresis

  2. IVIg