Myasthenia Gravis

Question 1

What is myasthenia gravis?

Answer 1

Autoimmune disease against Nicotinic Acetylcholine Receptors (AChR) in the neuromuscular junction

Question 2

Who is more likely to get MG if UNDER the age of 50 and what is it associated with?

Answer 2

Commoner in women if under 50 and associated with autoimmune disease.

Question 3

Who is more likely to get MG if OVER the age of 50 and what is it associated with?

Answer 3

Commoner in men and is associated with thymic atrophy or thymic tumour, rheumatoid arthritis and SLE

Question 4

Briefly describe the pathophysiology of autoimmune associated myasthenia gravis?

Answer 4

• Autoantibodies to nicotinic acetylcholine receptor
  Interfering with the NMJ via depletion of working post-synaptic receptor sites
• This is achieved by immune complex deposition of anti-AChR IgG and complement at the post-synaptic membranes, causing interference with and destruction of receptors
• Both B and T cells are implicated
• This blocks the excitatory effect of ACh on the nicotinic receptors (since there are less receptors) resulting in muscle weakness

Question 5

What is the overall presentation of myasthenia gravis?

Answer 5

Increasing muscular fatigue, in particular on repetitive or sustained movement. Improves with rest.

Question 6

What muscle groups tend to be affected and in what order?

Answer 6

1. Extra-ocular
2. Bulbar - swallowing & chewing
3. Face
4. Neck
5. Trunk

Question 7

What signs in the eyes would you look for in myasthenia gravis?

Answer 7

• Look for ptosis (drooping of upper eyelid),
• Diplopia (double vision)
• Myasthenic snarl on smiling