1.4 Myasthenia Gravis II

Question 1

What kind of condition is Myasthenia Gravis?

Answer 1

Autoimmune condition, a potentially life-threatening condition.

Question 2

What are the three paediatric versions of myasthenia gravis?

Answer 2

Neonatal – Born to a myasthenic mother. Disease is self-limiting (in 6 weeks approx.)
Congenital – Infants born to non-myasthenic mothers.
Juvenile – Develops between infancy and puberty. More spontaneous remissions than adults, slower progress.

Question 3

What are the two adult versions of myasthenia gravis?

Answer 3

Ocular – Limited to the eye muscles.
Generalised – Fatigability of striated muscle: bulbar, limbs, facial, respiratory.
(Drug related)

Question 4

What are the causes of myasthenia gravis?

Answer 4

Enlarged/tumourous thymus gland (in the chest) – Thymus gland is involved in developing the immune system in childhood, specifically T cells, it then should shrink in adulthood however in many cases of MG it remains large.

Question 5

What can be associations of myasthenia gravis

Answer 5

Thyroid dysfunction
More common in other auto immune conditions such as lupus or rheumatoid arthritis.

Question 6

What are the general signs and symptoms of generalised myasthenia gravis?

Answer 6

Fatigue
Lack of energy

Question 7

What are the bulbar signs/symptoms in generalised myasthenia gravis?

Answer 7

Problems with speech

Question 8

What are the limb girdle signs/symptoms in generalised myasthenia gravis?

Answer 8

Difficulty getting out of a chair
Difficulty climbing stairs

Question 9

What are the respiratory signs/symptoms in generalised myasthenia gravis?

Answer 9

Problems breathing

Question 10

What are the facial signs/symptoms in generalised myasthenia gravis?

Answer 10

Lack of facial expression

Question 11

What are the ocular signs/symptoms of myasthenia gravis?

Answer 11

Ptosis - Variable, fatigable, often bilateral but can be asymmetrical
Diplopia - Can mimic multiple conditions including nerve palsies, gaze palsies and INO

Question 12

What are key points to note in history taking with myasthenia gravis?

Answer 12

Ask about variability and changes throughout the day
Any activities that make symptoms worse (ie exercise or heat)
Generalised symptoms (problems chewing, raising arms, movement)
General health conditions (other autoimmune conditions, diabetes, thyroid problems.

Question 13

What are the key observations to note in myasthenia gravis?

Answer 13

Frontalis overaction (use of brow to raise lids)

Question 14

What are key ocular movements to note in myasthenia gravis?

Answer 14

Variability during the exam and between visits - May mimic nerve palsies or restrictions, subtle or marked problems. Hess chart can be used to plot changes over visits (as can fields of BSV or fields of uniocular fixation). May vary or increase during assessment but can take more than one visit to see variability in symptoms.
Increase in limitations on sustained gaze
Normal saccades but fatigue quickly

Question 15

What are the clinical tests that can be done to identify myasthenia gravis?

Answer 15

Enhanced ptosis (Gorelick’s sign)
Cogans lid twitch
Sustained elevation (Simpson’s test)
Peek sign
Ice pack test

Question 16

Breifly explain the enhanced ptosis (Gorelick’s sign) method.

Answer 16

Lift more ptotic lid and other side increases due to Herrings law of equal innervation.

Question 17

Briefly explain the Cogans lid twitch method.

Answer 17

Patient looks down for 15s then makes quick refixation to PP, ptotic lid moves above previous position before returning to ptotic position.

Question 18

Briefly explain the sustained elevation (Simpson’s test) method.

Answer 18

Patient elevates eyes for 2 minutes, lids slowly fatigue, or patient has difficulties maintaining fixation.

Question 19

Briefly explain the peek sign method.

Answer 19

Patient can’t bury lashes or prevent eyes being opened with slight pressure. Orbicularis weakness.

Question 20

Briefly explain the ice pack test method.

Answer 20

Ice pack held against ptotic eye for 2 mins. Ptosis should be noted to improve by >2mm. Diplopia may also improve. This method works due to the biochemical basis principle of low temperatures enhancing neuromuscular transmission.

Question 21

What are some further investigations that can be done to diagnose myasthenia gravis?

Answer 21

Bloods - Acetylcholine or MuSK antibodies.
Thymus imaging - looking for enlargement.
Single fibre EMGs

Question 22

What are some medical treatments for myasthenia gravis?

Answer 22

Thymectomy - the removal of the thymus gland surgically
Pyridostigmine (anti-acetylcholinesterase)
Cortico-steroids (prednisolone)

Question 23

What are some orthoptic treatments for myasthenia gravis?

Answer 23

Prisms – often not helpful due to variability
Occlusion – foil/patch
Ptosis props – uncomfortable
Patient information – charities