Myasthenia gravis

  • Acquired
  • Autoimmune
  • 5 per 100,000 people
  • Antibodies are present at the neuromuscular junction resulting in impaired neurotransmission

Can be due to Thymoma

Age:

  • Non-thymoma = peak age 10-30 and another peak 60-70yrs
  • thymoma related – 40-50 years
  • In under 40yr olds affects Females more than males
  • In over 50yr olds affects males more than females
  • 10% are children

Clinical Features:

  • Weakness -fluctuating  – worse at end of day – muscles are easily fatigued – progressive with exercise
  • Weakness in
    • Periocular – causing ptosis (can be bilateral) and diplopia
    • facial
    • bulbar (muscles of articulation)
    • Girdle

15% get life – threatening Respiratory weakness Myaesthenia Crisis 

  • Commonly starts with eye signs and
  • Two thirds progress to generalised disease
  • Progression is generally within two years

Diagnosis:

  • Clinical history + neuro exam
  • Neurodiagnostic + antibodies at neuromusc junction
  • Acetylcholine receptor antibodies (IgG) – present in 85% of general Myasthenia and 50% of occular
  • The Tensilon test is useful – where Tensilon a short acting anticholinesterase is given IV is positive in patients who have an improvement in muscle strength

Management

  • Most respond well to immunosupression
    • Prednisolone
    • azathioprine / cyclosporin / mycophenolate
  • If evidence of thymoma
    • thymectomy
  • Myasthenia crisis
    • plasmaphoresis or IV immunoglobulin