User Tools

Site Tools


myasthenia_gravis

myasthenia gravis

Introduction

  • an autoimmune condition, which, in the early stages, mostly affects the muscles that control eye movement, facial expression, chewing and swallowing. As the condition progresses, neck and limb muscles may also be affected, causing difficulty with holding the head up, walking upstairs and raising the arms, and later breathing may be affected.
  • affects 1 in 10,000 people
  • can develop at any age, but unusal for those under age 15yrs except in some Asian countries
  • under age 40yrs, women are 3x more likely than men to get it
  • over age 50yrs, men are more likely to get it

aetiology

  • 65% have thymic hyperplasia
  • 15% myasthenia gravis have a thymoma
  • autoantibodies
    • 85% of patients with myasthenia gravis produce antibodies against a protein called acetylcholine receptor (AChR)
    • 5% have antibodies to a protein called muscle-specific kinase (MuSK)
    • the other 10% presumably have other antibodies yet to be determined such as against LRP4

myasthenia gravis crisis

  • a crisis occurs when the muscles involved in respiration are affected causing SOB
  • 15-20% of myasthenia gravis patients will develop a crisis
  • requires admission for supported breathing on a ventilator
  • precipitants include:
    • physical stress
    • pregnancy
    • infection
    • some medications (see below)
    • 50% of cases are idiopathic

  • many medications interfere with NM transmissions and may cause severe weakness in patients with myasthenia gravis - generally these medications are contraindicated such as:
    • many antibiotics:
      • aminoglycoside such as gentamicin
      • fluoroquinolones such as ciprofloxacin
      • tetracyclines including clindamycin
      • macrolides such as azithromycin
      • sulphonamides
      • quinolones
    • other medications:
      • beta blockers
      • calcium channel blockers
      • procainamide
      • anticonvulsants such as barbiturates, phenytoin
      • lithium
      • antipsychotics such as phenothiazines (chlopromazine), haloperidol
      • tricyclic antidepressants
      • amphetamines
      • ritonavir
      • quinidine
      • quinine
      • chloroquine
      • magnesium (avoid hypermagnesaemia)

myasthenia_gravis.txt · Last modified: 2018/10/10 06:44 by wh