Myasthenia Gravis

Question 1

what occurs in myasthenia gravis

Answer 1

autoimmune disease

• antibodies block/destroy nicotinic acetylcholine receptors at the NMJ
• prevents nerve impulses from triggering muscle contractions
• FATIGUABLE

Question 2

what are the types of MG

Answer 2

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)

Question 3

what are common signs/symptoms of ocular MG

Answer 3

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)

Question 4

what are common signs/symptoms of bulbar MG

Answer 4

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)

Question 5

what are common signs/symptoms fo generalised MG

Answer 5

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

Question 6

what is a myasthenic crisis

Answer 6

paralysis of the respiratory muscles, needs assisted ventilation

Question 7

what can trigger a myasthenic crisis

Answer 7

infection, fever, adverse drug reaction, emotional stress, starting high dose steroids

Question 8

what can be found on neuro exam in MG

Answer 8

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

Question 9

what investigations can be done for MG

Answer 9

EMG
blood tests - antibodies
CXR - look for thymoma!
vitalograph

Question 10

what antibodies are involved in MG

Answer 10

most common = anti acetylcholine receptor antibodies

more rare, affects face only = anti MUSK antibodies

Lambert - Eaton = anti voltage gated calcium channel antibodies

Question 11

what is a vitalograph and how can it help with monitoring

Answer 11

measures patients vital capacity

as soon as a downward trend begins = respiratory muscles are being affected by MG - may need resp support/ventilation/intubation

Question 12

what is the first line management of MG

Answer 12

steroids - VERY LOW DOSE then build up

acetylcholinesterase inhibitors eg pyridostigmine

Question 13

what are the side affects of the first line drugs

Answer 13

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

Question 14

what is the second line management of MG

Answer 14

if patients condition worsens

Immunoglobulins - IV

plasmapheresis - removes ab from blood

Question 15

what is the best longterm management for MG

Answer 15

steroid sparing drugs eg
azathioprine
rituximab

still immunosuppressive but without all the side effects of steroids

Question 16

what are some side effects of steroids

Answer 16

increased risk of infection
diabetes (need BG monitored)
cushingoid syndrome
glaucoma, cataracts (need eye check ups)
osteoporosis (need dexa scans)

Question 17

who should be involved in the treatment of a patient with MG

Answer 17

MDT:

PT, OT, doctors, nurses, speech+language therapist, dietician

Question 18

how do you check for fatiguability in an examination

Answer 18

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