Myasthenia Gravis

Question 1

What is myasthenia Gravis?

Answer 1

Myasthenia gravis is an autoimmune condition affecting the neuromuscular junction. It causes muscle weakness that progressively worsens with activity and improves with rest.

Question 2

When does myasthenia gravis affect men? Women?

Answer 2

Women <40
Men >60

Question 3

What is myasthenia gravis often associated with?

Answer 3

Thymomas

Question 4

What 3 antibodies are associated with myasthenia gravis?

Answer 4

AChR antibodies
MuSK antibodies
LRP4 antibodies

Question 5

What neurotransmitter is released from presynaptic membranes in neuromuscular junctions?

Answer 5

ACh

Question 6

What is the action of AChR antibodies?

Answer 6

Bind to postsynaptic ACh receptors
Blocks them and prevents stimulation by ACh
More the receptors are used during activity the more they become blocked

Activate complements system leading to damage of postsynaptic membrane

Question 7

What is the action of MuSK and LRP4 proteins? What do antibodies against them lead to?

Answer 7

Proteins create and organise the ACh receptor
Antibodies lead to inadequate ACh receptor

Question 8

What are the main symptoms of myasthenia gravis? (7)

Answer 8

• Difficulty climbing stairs, standing from a seat or raising their hands above their head
• Extraocular muscle weakness, causing double vision (diplopia)
• Eyelid weakness, causing drooping of the eyelids (ptosis)
• Weakness in facial movements
• Difficulty with swallowing
• Fatigue in the jaw when chewing
• Slurred speech

Question 9

What ways can you elicit fatiguability in myasthenia gravis? (3)

Answer 9

○ Repeated blinking will exacerbate ptosis
○ Prolonged upward gazing will exacerbate diplopia on further testing
○ Repeated abduction of one arm 20 times will result in unilateral weakness when comparing both sides

Question 10

What do antibody tests look for in myasthenia gravis? (3)

Answer 10

• AChR antibodies (around 85%)
• MuSK antibodies (less than 10%)
• LRP4 antibodies (less than 5%)

Question 11

What imaging is used in myasthenia gravis and why?

Answer 11

A CT or MRI of the thymus gland is used to look for a thymoma.

Question 12

What is the diagnostic test in myasthenia gravis?

Answer 12

Edeophonium test

Question 13

What is the action of cholinesterase enzymes?

Answer 13

Work in the NMJ to break down ACh

Question 14

What is the action of the edrophonium test?

Answer 14

Patient given edrophonium chloride
This blocks cholinesterase enzymes .: ACh breakdown is reduced
.: level of ACh in NMJ increases temporarily relieving the weakness

Question 15

What are the management options in myasthenia gravis? (4)

Answer 15

○ Pyridostigmine is a long acting cholinesterase inhibitor that prolongs the action of acetylcholine and improves symptoms
○ Immunosuppression (e.g., prednisolone or azathioprine) suppresses the production of antibodies
○ Thymectomy can improve symptoms, even in patients without a thymoma
○ Rituximab (a monoclonal antibody against B cells) is considered where other treatments fail

Question 16

What is myasthenic crisis?

Answer 16

Myasthenic crisis is a potentially life-threatening complication of myasthenia gravis. It causes an acute worsening of symptoms, often triggered by another illness, such as a respiratory tract infection. Respiratory muscle weakness can lead to respiratory failure. Patients may require non-invasive ventilation or mechanical ventilation.

Question 17

What is the management of myasthenic crisis? (2)

Answer 17

IV immunoglobulins
Plasmapheresis to remove bad antibodies

Question 18

Which drug type is avoided in myasthenia gravis?

Answer 18

Beta blockers