myasthenia gravis Flashcards
what
autoimmune condition causing muscle weakenss that gets worse with activity and improves with rest
usual age of onset
women <40yrs
men >60yrs
strong link with
thymoma
pathophysiology
Ach receptor antibodies bind to NMJ receptors
blocks Ach from being able to bind and stimulate muscle contraction
antibodies also activate complement system leading to damage to cells at postsynaptic membrane
presentation
weakness worse w use and better w rest
- eye muscle weakness = diploplia
- eye lid weakness = ptosis
- weak facial movements
- difficulty swallowing
- fatigue wehn chewing
- slurred speech
- progressive weakness w repetitive movement
signs OE
- repeated blinking exacerbates ptosis
- prolonged upward gaze excacerbates dilplopia
- repeated abduction one arm results in unilateral weakness
check for thymectomy scar
test FVC
antibodies
ACh receptor antibodies
muscle specific kinase antibodies
low density lipoprotein-realated anibodies
Ix
antibodies
CT or MRI thymus gland
edrophonium test
Edrophonium Test
give IV dose of edrophonium chloride which blocks cholinesterase enzymes breaking down Ach
Ach increases at NMJ
temporarily releives weakness
Mx
reversible Ach inhibitors - pyridostigmine or neostigmine
- immunosuppression (prednisilone, azathioprine)
- thymemcotmy
Mx if standard Rx not working
rituximab
Myasthenic Crisis
acute worsening of symptoms usually triggered by another illness e.g. resp infection
can lead to resp failure due to weakness resp muscles
Myasthenic Crisis Mx
may need NIV + BiPAP or I&V
Immunomodulatory therapies
- IV Ig
- plasma exchange
what drugs can exacerbate it
penicillamine quididine, procainamide beta blockers lithium phenytoin gentamicin macrolides quinolones tetracyclines
