Myasthenia Gravis

Question 1

What is myasthenia gravis?

Answer 1

AI condition with Abs directed against the acetylcholine receptors on the post-synaptic muscle membrane.

Question 2

What is the aetiology of myasthenia gravis?

Answer 2

Thymus is abnormal in ~75%: 65% have hyper plastic thymus, ~10% have thymic tumours.

Question 3

What is the epidemiology of myasthenia gravis?

Answer 3

1 in 7500

Female: Male = 3:2

Question 4

What are the signs symptoms of myasthenia graves?

Answer 4

Weakness, fatiguability; often affects cranial muscles early leading to ptosis, diplopia, dysarthria, dysphagia.
Limb weakness often proximal.

Question 5

What is a myasthenic crisis?

Answer 5

When respiratory function is affected.

Question 6

What Ix in myasthenia gravis?

Answer 6

Acetylcholine receptor antibodies; 
CXR/CT (to look at thymus), 
anti cholinesterase/edrophonium test (Tensilon test), 
nerve conduction studies, 
thyroid function, 
spirometry.

Question 7

Rx Myasthenia Gravis?

Answer 7

• Medical: anti-cholinesterase e.g. pyridostigmine
• Surgery: thyrectomy -> improves 85%
• Immunosuppression: steroids, azathioprine, ciclosporin, mycophenolate mofetil, cyclophosphamide (rarely).
• Emergency: Iv Ig, plasmapharesis