Myasthenia Gravis Flashcards
what occurs in myasthenia gravis
autoimmune disease
- antibodies block/destroy nicotinic acetylcholine receptors at the NMJ
- prevents nerve impulses from triggering muscle contractions
- FATIGUABLE
what are the types of MG
main:
- ocular (eye only)
- bulbar (pharynx/larynx/lowerCN)
- generalised
others:
congenital myasthenia syndrome (genetic, paeds)
Lambert-eaton myasthenia syndrome (para-neoplastic syndrome that presents as MG)
what are common signs/symptoms of ocular MG
ptosis (drooping - levator palebrae superioris weakness)
diplopia (double vision - extraocular weakness
general eye muscle weakness (above + orbicularis oculi)
dryness (not being able to close eyes properly due to weakness)
what are common signs/symptoms of bulbar MG
difficulty swallowing (dysphagia)
motor of speech (dysarthria - muscle problem, slow/slurred)
weak muscles of mastication (hanging jaw sign)
weakness of the tongue (can flop back easily when lying down)
what are common signs/symptoms fo generalised MG
all of ocular and bulbar as well as
- proximal weakness
- head and neck weakness
- SOB from weakness in muscles controlling breathing/diaphragm - ask if improved when sitting instead of lying down
- early morning headaches - from hypoventilation during the night not blowing off enough CO2
what is a myasthenic crisis
paralysis of the respiratory muscles, needs assisted ventilation
what can trigger a myasthenic crisis
infection, fever, adverse drug reaction, emotional stress, starting high dose steroids
what can be found on neuro exam in MG
tone - usually normal but can be slightly lowered
reflexes - normal
power - can be reduced after fatiguing
coordination - normal - if seems uncoordinated make sure its not just from weakness
sensation - normal
what investigations can be done for MG
EMG
blood tests - antibodies
CXR - look for thymoma!
vitalograph
what antibodies are involved in MG
most common = anti acetylcholine receptor antibodies
more rare, affects face only = anti MUSK antibodies
Lambert - Eaton = anti voltage gated calcium channel antibodies
what is a vitalograph and how can it help with monitoring
measures patients vital capacity
as soon as a downward trend begins = respiratory muscles are being affected by MG - may need resp support/ventilation/intubation
what is the first line management of MG
steroids - VERY LOW DOSE then build up
acetylcholinesterase inhibitors eg pyridostigmine
what are the side affects of the first line drugs
steroids - if dose too high can trigger a myasthenic crisis as when starting on steroids patients get worse before they get better
pyristigmine - works by stimulating muscle contractions so can cause severe stomach cramping and diarrhoea
what is the second line management of MG
if patients condition worsens
Immunoglobulins - IV
plasmapheresis - removes ab from blood
what is the best longterm management for MG
steroid sparing drugs eg
azathioprine
rituximab
still immunosuppressive but without all the side effects of steroids
what are some side effects of steroids
increased risk of infection diabetes (need BG monitored) cushingoid syndrome glaucoma, cataracts (need eye check ups) osteoporosis (need dexa scans)
who should be involved in the treatment of a patient with MG
MDT:
PT, OT, doctors, nurses, speech+language therapist, dietician
how do you check for fatiguability in an examination
eyes - check eye movements/power of eyelids then ask them to look up for ~30 seconds then check again
upper limb - do 15 “chicken wings” on one arm then check power between both arms
lower limb - test power the ask them to walk around for a bit - check again and should be reduced
