myasthenia gravis Flashcards
what is myasthenia gravis
autoimmune disease characterised by weakness of skeletal muscle
which autoantibodies are formed in MG
autoantibodies against nicotinic acetylcholine receptors in skeletal muscle
epidemiology of myasthenic crisis
20% of patients
epidemiology of MG
5.3/100, 000 a year, mortality of 0.1-0.9/100, 000
aetiology of MG
20-30 in F, 60-80 in M
normal neuromuscular junction action
- action potential opens Ca2+ channels 2. calcium influx 3. acetylcholine exocytosis 4. activation of nicotinic receptors 5. sodium influx 6. muscle contraction
how is the muscular junction affected by MG
loss of nicotinic receptors at post synaptic cleft - weakened muscle contraction
first signs/symptoms
ocular - ptosis, dipoplia, restricted eye movements
other symptomsof MG
lack of facial expressions slurred speech difficulty chewingdysphagia weakness in arms, legs, neck shortness of breath
how to diagnose MG
ice test, auto antibody blood test, neurophysiology, edrophonium test
what is the ice test
cools the muscles, should improve symptoms
how is neurophysiology used to diagnose
electromyogram measures muscle compound action potential in response to repeated stimulation - should see decrease in muscle response
what is the edrophonium test
short acting choline esterase inhibitors, should reverse ptosis (lots of side effects!)
what are the treatment options for MG
acetylcholinesterase inhibitors - pyridostigmine immunosuppressants IV immunoglobulin/plasma exchange thymectomy
what is a short acting acetylcholinesterase inhibitor
edrophonium
