Myasthenia gravis (MG)

Question 1

1) What is myasthenia gravis?
2) What effect does rest have on MG?
3) What effect does activity have on MG?

Answer 1

1) Autoimmune condition that causes muscle weakness
2) Makes it better
3) Makes it worse

Question 2

1) When does it usually affect men?
2) When does it usually affect women?

Answer 2

1) Over 60s
2) Under 40s

Question 3

There is a strong link between MG and what other condition?

Answer 3

Thymoma - tumour of thymus gland

Question 4

1) In MG, autoantibodies are generated against what?
2) What do these autoantibodies bind to?
3) What is the consequence of this?
4) In MG, why is there less effective stimulation of the muscle with increased activity?
5) What are the 2 other, less common, autoantibodies seen in MG?

Answer 4

1) Acetylcholine receptor antibodies
2) Postsynaptic neuromuscular junction receptors
3) Blocks the receptor and prevents the acetylcholine from being able to stimulate the receptor and trigger muscle contraction
4) As the receptors are used more during muscle activity, more of them become blocked up
5) Muscle-specific kinase (MuSK) and LRP4 autoantibodies

Question 5

1) What is the characteristic feature/symptom of MG?
2) Name 3 other symptoms of MG

Answer 5

1) Weakness that gets worse with muscle use and improves with rest
2) Diplopia, ptosis, weakness in facial movements, dysphagia, fatigue in the jaw when chewing, slurred speech

Question 6

How can MG be diagnosed?

Answer 6

Direct testing for the relevant autoantibodies

Question 7

1) Reversible acetylcholinesterase inhibitors can be used in the management of MG - name 1 of these
2) How do they work?
3) Name an immunosuppressive drug that can be used to suppress the production of autoantibodies
4) Name a monoclonal antibody that can be used, and what is it targeted at

Answer 7

1) Neostigmine, pyridostigmine (long acting)
2) Increases the amount of acetylcholine in the neuromuscular junction by decreasing acetylcholine breakdown
3) Prednisolone, azathioprine
4) Rituximab (B cells), eculizumab (complement protein C5)

Question 8

What is a myasthenic crisis?

Answer 8

severe complication og MG where there’s acute worsening of symptoms, often triggered by another illness. It can lead to respiratory failure as a result of weakness in the muscle of respiration

Question 9

Name a medication that may exacerbate myasthenia gravis

Answer 9

• Beta blockers
• Penicillamine
• Lithium
• Quinidine and procainamide
• Antibiotics i.e. macrolides, gentamicin, quinolones, tetracyclines
• Phenytoin