Musculoskeletal System >
Myasthenia Gravis

“Chronic autoimmune, type 2 hypersensitivity, inflammatory disease of the neuromuscular junction causing skeletal muscle weakness

Risk Factors
  • Modifiable:
    • Smoking
  • Non-Modifiable:
    • Females under 40
    • Males over 60
    • Mother with myasthenia gravis(MG) in neonatal MG
Aetiology
  • Antibody to component of neuromuscular junction causing fatigable muscle weakness
Pathophysiology
  • B cell producing autoantibody to nAch Receptor:
    • ACh unable to bind => complement activation => inflammation and destruction of myocytes =>↓ACh receptor => ↓muscle contraction
  • B cell producing muscle-specific receptor tyrosine kinase( MuSK) autoantibodies
    • Target intracellular muscle protein=> myocyte destruction =>↓muscle destruction
  • Paraneoplastic syndrome (bronchogenic carcinoma, thymic neoplasm)
    • Cancer cells producing autoantibodies to a component of NMJ => myocyte destruction =>↓muscle contraction
Clinical Presentation
  • Muscle weakness that worsens with activity and improves with rest.
  • Extraocular muscle weakness (ocular myasthenia)
  • Ptosis
  • Diplopia
  • Change in facial expression
  • Difficulty swallowing
  • Dyspnoea
  • Dysarthria
  • Limb weakness
Investigations
  • Bloods (anti-AChR, anti-MuSK or anti-LRP4 and thyroid function)
  • Edrophonium test
  • Single fibre electromyography
  • Chest CT or MRI(thymoma)
  • Brain MRI
Management
  • Anticholinesterase (neostigmine, pyridostigmine)
  • Immunosuppressant (prednisone, azathioprine, cyclosporin, mycophenolate mofetil, tacrolimus)
  • Thymectomy
Complications
  • Myasthenic crisis (weakness of respiratory muscles)
  • Aspiration pneumonia

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