Myasthenia Gravis

Question 1

what is the prevalence of myasthenia gravis?

Answer 1

15 per 100,000 in the UK

Question 2

what are the three different presentations of Myasthenia Gravis?

Answer 2

pure ocular Myasthenia Gracis

generalised Myasthenia Gravis

Crises (Myasthenic and cholinergic crisis)

Question 3

what is one of the most common symptoms of ocular MG

Answer 3

ptosis (drooping /fatigue of eyelid)

Question 4

what are some common features of Generalised Myasthenia Gravis?

Answer 4

usually ocular disease plus weakness of another muscle group such as :

bulbar function
proximal weakness
respiratory weakness

Question 5

what clinical examination is useful in myasthenia gravis?

Answer 5

test for muscle fatigue

Question 6

what investigations are useful when diagnosing myasthenia gravis?

Answer 6

antibody tests
edrophonium test
EMG

Question 7

what is the ice test?

Answer 7

when ice is applied to the eye lids, the patient can open their eyes for around 40 seconds, then the eyes begin to fatigue

Question 8

what antibodies can be tested for when looking for myasthenia gravis?

Answer 8

anti acetylcholine receptor (85%)

anti MUSK (7%)

around 7 % no antibody is found (suggest another unfound)

Question 9

what is the edrophonium test and how does it work?

Answer 9

edrophonium is an acetly choline-esterase inhibitor

it can temporarily reverse myasthenia gravis signs

administed IV and in a double Blind fashion

Question 10

what are the typical EMG features seen in myasthenia gravis?

Answer 10

decremental loss of the compound muscle action potential (CMAP)

and on a single fibre EMG, the phenomenon of jitter and block is seen

Question 11

what is jitter and block?

Answer 11

jitter the phenomeneon of a delay between the firing of muscles more distal to the nerve.

block is when the more distal muscle fibres never actually fire.

Question 12

what are the three treatment mechanisms for myasthenia gravis

Answer 12

increasing the synaptic cleft acetylcholine concentration

avoiding immune mediated end plate damage

removing antibodies and their production (plasmapherisis)

Question 13

what two drugs can be used to test for Myasthenia Gravis

Answer 13

Neostigmine
pyridostigmine

block the breadown of acetylcholine by acetylcholine esterase in the synapse hence increasing the amount of acetylcholine available for the receptor

not used for treatment as they have cardiac risks

Question 14

what treatments are used for myastenia gravis

Answer 14

steroids

azathioprine
methotrexate
cyclosporin
cyclophosphamide
rituximad

plasmaphoresis ( in severe cases)