Neuromuscular Junction Disorders

Question 1

what causes myasthenia gravis to present

Answer 1

autoimmune condition due to the production of antibodies against nicotinic receptors at the neuromuscular junction

Question 2

what are the 2 antibodies produces in MG

Answer 2

anti-AChR and anti-MuSK

Question 3

what effect does the auto-antibodies have on muscles

Answer 3

reduces the overall number of receptors leading to muscle weakness and fatiguability

Question 4

what conditions is MG associated with

Answer 4

thymus disorders - hyperplasia in younger people and atrophy/tumours in older people
SLE and rheumatoid

Question 5

what causes the muscle weakness associate with MG to worsen

Answer 5

pregnancy
exercise
used of beta-blockers, opiates, gentamicin and tetracyclines

Question 6

myasthenia gravis is more common in men or women

Answer 6

women, peaks in early 30s

Question 7

describe the pattern of muscle weakness in myasthenia gravis

Answer 7

fluctuating and fatiguing muscle weakness that worsens as the day goes on and with repeated used of the muscle

Question 8

in order, describe the muscle groups affected by myasthenia gravis

Answer 8

extraocular - causing ptosis and double vision
bulbar - dysphagia, difficulty chewing, dysarthria
face - drooping of facial muscles and snarled expression
neck/trunk - causing difficulty breathing

Question 9

what is Peek’s sign

Answer 9

when patients close eyes tightly, sclera will show

Question 10

describe sensation, tone and reflexes in a patient with myasthenia gravis

Answer 10

normal, just reduced power

Question 11

how is myasthenia gravis diagnosed

Answer 11

immunology for autoantibodies
give an ACh inhibitor and symptoms should improve immediately
neurophysiology - low amplitude action potentials and reduction in muscle twitches

Question 12

how is myasthenia gravis managed

Answer 12

anti-cholinesterase - pyridostigmine which reduces the breakdown of ACh in the synapse
if there is a thymus abnormality do thymectomy

Question 13

what is the main complication of myasthenia gravis

Answer 13

myasthenic crisis

Question 14

how does myasthenic crisis present

Answer 14

severe relapse resulting in weakness of respiratory muscles and difficulty breathing - give ventilatory support and IV plasmaphoresis

Question 15

where in the synapse does lambert eaton syndrome affect

Answer 15

pre-synaptic calcium channels

Question 16

what is the effect of lamber eaton syndrome

Answer 16

limits the amount of ACh that can be released from presynaptic terminals

Question 17

what are the 2 main causes of lambert eaton syndrome

Answer 17

autoimmune - anti-P/Q CGCC antibodies

paraneoplastic syndrome - particularly small cell lung cancer

Question 18

lambert eaton presents very similarly to myasthenia gravis, what are the differentiating features of lambert eaton syndrome

Answer 18

improvement on exercise
begins with limb disturbance then gait then ocular symptoms
autonomic involvement - dry mouth, constipation and impotence
hyporeflexia

Question 19

what are the neurophysiology findings for lambert eaton syndrome

Answer 19

low frequency muscle action potentials and increase in twitch amplitude with exercise

Question 20

how is lambert eaton syndrome managed

Answer 20

3, 4 diaminopyridine

immunosuppression