Myasthenia Gravis Flashcards
def
an autoimmune disease mediated by antibodies to nicotinic acetylcholine receptors (AChR), which interfere with the neuromuscular transmission via depletion of working post-synaptic receptor sites
this produces weakness of skeletal muscles
are b cells or t cells implicated
both
aetiology
impairment of neuromuscular junction transmission
this occurs by auto-antibodies against the nAChR
what conditions is myasthenia gravis associated with
pernicious anaemia
epi
<50yrs is more common in women
-associated with thymic hyperplasia
>50yrs is more common in men
-associated with thymic atrophy
history
increasing muscular fatigue -worse towards end of the day and with repetitive use ptosis + diplopia facial weakness -difficulty smiling, chewing, swallowing
what order are muscle groups affected in myasthenia gravis
1 extraocular 2 bulbar (swallowing + chewing) 3 face 4 neck 5 iimbs 6 trunk
examination
1 eyes
-bilateral ptosis
-opthalmoplegia (paralysis of eye muscles)
2 bulbar
-reading aloud can cause slurred or progressively quieter speech
3 limbs
-testing power before and after repeated use of muscle
how would you test ocular fatigue
ask patient to look upwards for 1 minute and observe for ptosis
what is the ‘ice on eyes’ test
placing ice on closed eyelids can reduce ptosis
a positive sign is improval of ptosis by >2mm
investigations
1 bloods -CK levels to exclude myopathies -observe for anti-nAChR antibodies 2 nerve conduction study -progressive decrease in muscle response (AP) with repetitive nerve stimulation -differentiates between myasthenia gravis + lambert eaton syndrome 3 imaging -of thymus
what condition is indicated with anti-voltage gated calcium channel antibody
lambert-eaton syndrome
what worsens weakness myasthenia gravis
pregnancy
hypokalaemia
beta-blockers
