Myasthenia Gravis

Question 1

What signs are seen in LMN conditions?

Answer 1

weakness
hypotonia
fasciculations

Question 2

where do motor cell bodies arise?

Answer 2

ventral (anterior) horns of the spinal cord

Question 3

What is the name of the synapse formed between neurones and muscle?

Answer 3

motor end plate

Question 4

How many motor neurones do each muscle cell respond to?

Answer 4

1

Question 5

what is the process behind muscle contraction?

Answer 5

action potential moves along the nerve
depolarisation
calcium channels open allowing Ca2+ influx
ACh released into the synaptic cleft

Question 6

which enzyme terminates the action of ACh?

Answer 6

acetylcholinesterase splits Ach into acetate and choline

Question 7

What is curare?

Answer 7

plant extract used in arrow poisons

Question 8

What effect does curare have?

Answer 8

occupies Ach receptor but doesn’t open ion channels - no contraction - no breathing

Question 9

Name some presynaptic disorders

Answer 9

botulism - clostridium botulinum
botulinum toxin
Lambert Eaton Myasthenic syndrome

Question 10

What is Lambert Eaton Myasthenic Syndrome?

Answer 10

antibodies to presynaptic calcium channels leads to less vesicle release

Question 11

Which malignancy has a strong association with LEMS?

Answer 11

small cell lung carcinoma

Question 12

name a postsynaptic disorder?

Answer 12

myasthenia gravis

Question 13

What happens in Myasthenia Gravis?

Answer 13

antibodies to acetylcholine receptors

reduced number of receptors = muscle weakness and fatiguability

Question 14

How do postsynaptic membranes become damaged?

Answer 14

antibodies trigger an inflammatory cascade that damages them

Question 15

What is the relation between the thymus and myasthenia gravis?

Answer 15

75% of patients have thymus hyperplasia or thymoma

Question 16

What are the common clinical features of MG?

Answer 16

worsening weakness throughout the day
extra ocular weakness
facial and bulbar weakness
limb weakness typically proximal

Question 17

How is MG treated?

Answer 17

Ach inhibitors

thymectomy

Question 18

Name an Ach inhibitor used to treat MG?

Answer 18

pyridostigmine

Question 19

Which medication should be avoided in the acute illness setting?

Answer 19

steroids - cause paradoxical worsening

Question 20

What causes death in MG patients?

Answer 20

respiratory failure and aspiration pneumonia

immunosuppressant side-effects

Question 21

Describe some features of smooth muscle

Answer 21

not striated
single central nucleus
gap junctions
actin myosin ratio 10:1

Question 22

What are Type 1 muscles?

Answer 22

slow oxidative - fatigue resistant

Question 23

What are type 2a muscles?

Answer 23

fast oxidative - aerobic metabolism

Question 24

What are Type 2b muscles?

Answer 24

easy glycolytic - easily fatigues

Question 25

What are fasciculations?

Answer 25

visible, fast twitches of muscle

Question 26

What are fasciculations a sign of in an unhealthy individual?

Answer 26

disease of the motor neurone, not the muscle

Question 27

What is myotonia?

Answer 27

failure of muscle relaxation after use

Question 28

Name some inflammatory muscle disorders?

Answer 28

dermatomyositis | polymyositis

Question 29

Name some inherited muscle disorders

Answer 29

muscular dystrophies

Question 30

What is polymyositis?

Answer 30

symmetrical, progressive proximal weakness developing over weeks to months

Question 31

What investigation findings are found in polymyositis?

Answer 31

raised CK

Question 32

how is polymyositis treated?

Answer 32

steroids

Question 33

What is the difference between dermatomyositis and polymyositis?

Answer 33

skin involvement - heliotrope rash underlying malignancy common

Question 34

What is characteristic in inclusion body myositis?

Answer 34

thumb sparing

Question 35

What is rhabdomyolysis?

Answer 35

dissolution of muscle, damage to muscle causes leakage of large quantities of toxic intracellular contents into plasma

Question 36

What is the common triad of rhabdo symptoms?

Answer 36

myalgia muscle weakness myoglobinuria

Question 37

Can drugs cause problems in muscle?

Answer 37

Yes - HMG co-enzyme A reductase inhibitors hydroxychloroquine amiodarone

Question 38

What is the most common muscular dystrophy?

Answer 38

myotonic dystrophy autosomal dominant weakness, cataracts, ptosis, balding, cardiac defects