Myasthenia Gravis

Question 1

What is Myasthenia Gravis?

Answer 1

An Autoimmune Condition affecting the Neuromuscular junction.

Question 2

When Does Myasthenia Gravis typically affect patients.

Answer 2

Men over 60.
Women under 40.

Question 3

What tumour has MG got a link with?

Answer 3

Thymomas (thymus Gland tumour)
10-20% of MG patients have one.
30% of Thymoma patients get MG.

Question 4

What neurotransmitter is being blocked in MG?

Answer 4

Acetylcholine.
(Usually stimulates muscle contraction)

Question 5

What happens to ACh Receptors in MG?

Answer 5

They are blocked by Acetylcholine Receptor (AChR) Antibodies.

The more receptors being used during muscle activity, leads to more becoming blocked. = Muscle weakness progressing with activity. Improves with rest.

Question 6

How is the complement system involved in increased cell damage in MG?

Answer 6

The AChR Antibodies activate the complement system when bound to post synaptic ACh Receptors, leading to cell damage and worsening symptoms further.

Question 7

What two other Antibodies can cause MG?

Answer 7

• Muscle-Specific Kinase (MuSK) antibodies.
• Low-density lipoprotein receptor-related protein 4 (LRP4) Antibodies.

MuSK and LRP4 proteins are important for the creation and organisation of ACh Receptors usually. Disruption leads to inadequate receptors.

Question 8

How does MG present?

Answer 8

Critical feature is weakness that worsens with muscle use and improves with rest.
- Typically best in morning and worse at night.
- Proximal muscles or limbs.
- Small muscles of Head and Neck.

• Extra-ocular muscle weakness (diplopia)
• Ptosis
• Slurred speech
• Fatigue in jaw.

Question 9

What are common investigations in MG?

Answer 9

• AChR antibodies (around 85%)
• Other antibodies.
• CT or MRI of Thymus gland.

The Edrophonium test

Question 10

What is the Edrophonium test?

Answer 10

• Patients injected with IV Edrophonium chloride.
• Blocks Cholinesterase Enzymes which usually breakdown ACh.
• Temporarily relieving the weakness.
  +ve result indicates MG.

Question 11

What is the Treatment for MG?

Answer 11

• Pyridostigmine (cholinesterase inhibitor)
• Immunosuppression (prednisolone, Azathioprine)
• Thymectomy (can improve symptoms even in px without Thymoma)
• Rituximab (monoclonal antibody against B cells) - considered where other Tx Fails.

Question 12

What is Myasthenic Crisis?

Answer 12

Life-threatening complication of MG.
Causes acute worsening of symptoms, often triggered by another illness.
- Respiratory muscles weakness can lead to Respiratory Failure.

Question 13

How is Myasthenic Crisis Treated?

Answer 13

• Ventillation.
• IV Immunoglobulins and Plasmapharesis.

Question 14

What medications should be avoided in MG patients?

Answer 14

beta blockers (bisoprolol)
- Can cause Respiratory issues (lowered FVC)