Myasthenia Gravis

Question 1

What is it?

Answer 1

Auto-immune disease affecting the NMJ

Question 2

Epidemiology?

Answer 2

affects men and women in different age ranges

• women mainly under 40
• men mainly over 60

Question 3

Aetiology?

Answer 3

thymus abnormalities in 75%

• hyperplastic thymus
• thymoma

Question 4

What are the antibodies implicated?

Answer 4

• Acetylcholine receptor antibodies
• MuSK
• LRP4

Question 5

What are MuSK and LRP4 antibodies targeted towards?

Answer 5

proteins which are involved in the production of ACh receptors. Destruction of these proteins makes inadequate ACh receptors

Question 6

Presentation?

Answer 6

• muscle weakness & fatigue, that gets worse with muscle activity and better with rest
• cranial muscles affected first
  
  • diploplia
  • ptosis
  • dysphagia
  • dysarthria
• proximal limb weakness

Question 7

Examination?

Answer 7

Tests to elicit muscle fatigue:

• blinking many times to exacerbate ptosis
• abduction of arm 20 times will result in unilateral weakness

Check for thymectomy scar

Check FVC

Question 8

Diagnosis?

Answer 8

• Antibody tests
• CT/MRI thymus
• Edrophonium test

Question 9

WHat is involved in the edrophonium test?

Answer 9

giving an IV dose of an acetylcholinesterase inhibitor (edrophonium chloride or neostigmine), which increases levels of ACh in the synapse. If this provides temporary relief from muscle weakness = diagnosis of MG

Question 10

Treatment?

Answer 10

• Reversible Acetylcholinesterase inhibitor
  
  • neostigmine
• Immunosuppression
• Thymectomy
• Rituximab

Question 11

What is a Myesthenic Crisis and what is the treatment for it?

Answer 11

Acute worsening of symptoms, usually triggered by another illness. Can lead to respiratory failure due to respiratory muscle weakness and pts may need intubated & ventilated.

Rx: Plasma exchange and IV Immunoglobulins