myasthenia gravis

Question 1

what is MG due to

Answer 1

decreased nicotinic AChR at NMJ, decreased end plate potentials and so doesnt trigger action potential

Question 2

what is MG characterised by

Answer 2

weakness and fatiguability of proximal limb, bulbar and ocular muscles

Question 3

what antibodies are found

Answer 3

antibodies to the Ach receptor protein (anti-AChR), also anti MuSK (muscle specific tyrosine kinase)

Question 4

features

Answer 4

fatiguability- proximal limb, extra ocular, speech, mastication, facial muscles all affected. resp difficulties. no muscle pain. thymic hyperplasia in 70% patients

Question 5

what can be found on examination

Answer 5

extra ocular palsies, ptosis. reflexes can be initially preserved but may be fatiguable

Question 6

what muscles are involved in patients who have antibodies against MuSK

Answer 6

facial, neck and bulbar muscles

Question 7

investigations

Answer 7

serum anti AChR and anti MuSK, nerve stimulation test- decrease in evoked muscle action potential, tensilon test (edrophonium), imaging MR for thymoma

Question 8

what is the main treatment

Answer 8

pyridostigmine- anti cholinesterase.

Question 9

what does pyridostigmine do and what are the side effects of anti cholinesterases

Answer 9

prolongs action of Ach by inhibiting the cholinesterase. side effects of colic and diarrhoea. if overdose get severe weakness- cholinergic crisis

Question 10

treatments

Answer 10

pyridostigmine, immunosuppressants- steroids, azathioprine; thymectomy; plasmapharesis and IV Ig