Myasthenia Gravis

Question 1

define myasthenia gravis?

Answer 1

• it is an autoimmune disease that affects the neuromuscular junction producing weakness in the skeletal muscles

Question 2

what is the etiology of myasthenia gravis?

Answer 2

• it is the impairment of the NMJ

- it is commonly due to autoantibodies against the nicotinic acetylcholine receptor

Question 3

what is lambert Eaton syndrome?

Answer 3

• it is a subtype of myasthenia gravis which is caused by autoantibodies that are against the presynaptic calcium channels, therefore leading to impairment of acetylcholine release.

Question 4

what are the risk factors of myasthenia gravis?

Answer 4

• it is associated with other autoimmune conditions

eg. pernicious anemia

Question 5

what is the epidemiology of myasthenia gravis?

Answer 5

it is present in 8-9/100,000 people so RARE

• it is more common in females at younger ages
• there is equal distribution at middle age

Question 6

presenting symptom of myasthenia gravis?

Answer 6

• muscle weakness that worsens with repetitive use
  or towards the end of the day
• ocular symptoms eg. ptosis,
• diplopia (double vision)
• Bulbar (CN9,10,11,12) symptoms eg. facial weakness
  , disturbed speech and difficulty smiling, chewing and swallowing

Question 7

presenting symptom in lambert eaton syndrome?

Answer 7

• it is muscle weakness that improves after repetitive use. Better in the evening than the morning

Question 8

what are the overall signs on examination of myasthenia gravis?

Answer 8

• signs can be generalized
• signs can be bulbar
• signs can be ocular
• signs can be limb related

Question 9

what are the major eye signs?

Answer 9

• ptosis

- Complex ophthalmoplegia

Question 10

how to check for ocular fatigue?

Answer 10

asking the patient tosustain and upward gaze for 1 minand watch the progressive ptosis that develops

Question 11

what is the ice on eyes test?

Answer 11

• Placing ice packs on closed eyelids for 2 mins can improve neuromuscular transmission andreduce ptosis

Question 12

what investigations should be undertaken for myasthenia gravis?

Answer 12

• bloods
• tensilon test
• nerve conduction study
• EMG
• CT thorax

Question 13

what will the bloods show?

Answer 13

• checks for Serum acetylcholine receptor antibody
• TFTs (there is an association with hyperthyroidism)
• creatinine kinase (to exclude myopathies)

Question 14

what bloods should be done for lambert eaton syndrome?

Answer 14

Anti-voltage gated calcium channel antibody

Question 15

what is the tensilon test?

Answer 15

• edrophonium bromide increases acetylcholine by preventing breakdown

Question 16

what will the nerve conduction study show?

Answer 16

• repetitive stimulation shows the decrement of muscle

Question 17

what will the CT thorax show?

Answer 17

• could show a thymoma