Myasthenia Gravis

Question 1

Myasthenia gravis is a condition affecting the neuromuscular junction of skeletal muscles. What is the cause of this disease?

1 - idiopathic
2 - autoimmune
3 - metabolic
4 - vascular

Answer 1

2 - autoimmune
- autoantibodies target nicotinic acetylcholine receptors on post synapse
- B and T cells are involved

Question 2

What is the prevalence of myasthenia gravis?

1 - 1.5-36.7 cases per 100,000
2 - 105-360 cases per 100,000
3 - 1500-3600 cases per 100,000
4 - 15,00-36,000 cases per 100,000

Answer 2

1 - 1.5-36.7 cases per 100,000
- this is a rare condition

Question 3

Are men or women more at risk of myasthenia gravis?

Answer 3

• women
• typically aged 20-30 y/o

Question 4

What type of hypersensitivity is myasthenia gravis classified as?

1 - type 1 hypersensitivity
2 - type 2 hypersensitivity
3 - type 3 hypersensitivity
4 - type 4 hypersensitivity

Answer 4

2 - type 2 hypersensitivity
- also called cytotoxic hypersensitivity
- T cells and complement pathway lead to cell damage, inflammation and apoptosis

Question 5

In myasthenia gravis is it just the acetylcholine receptors on the post synapse that are affected?

Answer 5

• no
• some patients produce another antibody that can enter skeletal muscle leading to apoptosis of skeletal muscle cells

Question 6

In myasthenia gravis the acetylcholine receptors on the post synapse or skeletal muscle cells can be damaged, inducing apoptosis due to autoantibodies. What has also been identified as a cause of myasthenia gravis?

1 - alcohol
2 - smoking
3 - metabolic syndrome
4 - paraneoplastic syndrome

Answer 6

4 - paraneoplastic syndrome
- bronchiogenic carcinoma or thymic neoplasm are most common causes
- malignancy induces and immune response and auto-antibodies, which subsequently targets the NMJ

Question 7

Myasthenia gravis can present with all of the following, but which is the tell tale sign?

1 - ptosis
2 - muscular weakness with fatigue
3 - bulbar (swallowing, chewing)
4 - facial/neck weakness
5 - limb girdle and trunk

Answer 7

2 - muscular weakness with fatigue
- exhausted in the evenings

Question 8

Which of the following are clinical signs of myasthenia gravis?

1 - dysphonia upon counting (slurred)
2 - ptosis and diplopia (double vision)
3 - myasthenia snarl when smiling
4 - peak signs of orbicularis (eyes opening despite you closing them)
5 - general weakness
6 - all of the above

Answer 8

6 - all of the above

Question 9

Although any skeletal muscles can be affected, which is often the most common?

1 - muscles of hands
2 - extra-ocular muscles
3 - respiratory muscles
4 - cardiac muscles

Answer 9

2 - extra-ocular muscles
- common to see ptosis (dropping) and diplopia (double vision)

Question 10

There are some common exacerbating factors of myasthenia gravis. Which of the following is NOT one of these?

1 - pregnancy
2 - low Na+
3 - exercise
4 - gentamicin
5 - beta blockers
6 - opiates

Answer 10

2 - low Na+
- low K+ can make patients worse
- the rest of these medications can act as neuromuscular blockade and make myasthenia gravis symptoms worse

Question 11

All of the following are typical differentials for myasthenia gravis, EXCEPt which one?

1 - polymyositis
2 - myopathies
3 - connective tissue disorders (SLE)
4 - stroke
5 - botulism
6 - Lambert-Eaton myasthenic syndrome

Answer 11

4 - stroke

Question 12

Patients who are suspected of having myasthenia gravis should be screened for ermatomyositis, polymyositis, systemic lupus erythematosus, Addison’s disease, Guillain-Barré syndrome and juvenile rheumatoid arthritis. What do all of these have in common?

1 - higher incidence in women
2 - occur at a younger age
3 - all autoimmune disease
4 - all of the above

Answer 12

3 - all autoimmune disease

Question 13

Which of the following is NOT a typically used test when trying to diagnose a patient with myasthenia gravis?

1 - ACh antibodies
2 - CK-MB
3 - EMG (decremental muscle response)
4 - CT to exclude malignancy (thyoma or bronchiogenic carcinoma)
5 - thyroid function

Answer 13

2 - CK-MB

Question 14

Can myasthenia gravis be dangerous and a risk to life?

Answer 14

• yes
• myasthenia crisis
• respiratory and/or cardiac depression

Question 15

What is the typical 1st line medication for patients with myasthenia gravis?

1 - Acetylcholinesterase inhibitors
2 - NMDA receptor antagonist
3 - Dopamine agonist
4 - Anticholinergics

Answer 15

1 - Acetylcholinesterase inhibitors
- increase ACh in synaptic cleft
- core drug for is Donepezil
- drug referenced in lecture was Pyridostigmine

Question 16

Acetylcholinesterase inhibitors are given as a symptomatic treatment for patients with myasthenia gravis. Which of the following is NOT typically a side effect of acetylcholinesterase inhibitors?

1 - diarrhoea
2 - abdominal pain common
3 - parasympathetic muscarinic
4 - tachycardia

Answer 16

4 - tachycardia
- typically causes bradycardia

Question 17

Acetylcholinesterase inhibitors is the typical 1st line medication for patients with myasthenia gravis. However, if a patient has a relapse or present with a myasthenia gravis crisis, what medication should they be given?

1 - Anticholinergics
2 - NMDA receptor antagonist
3 - Dopamine agonist
4 - Steroid

Answer 17

4 - Steroid
- specifically prednisolone
- need to use with caution as this can exacerbate myasthenia gravis symptoms

Question 18

Patients with myasthenia gravis can be given immunoglobulins via IV as part of immuno modulation. What is immunoglobulins as a treatment?

1 - patients are vaccinated to improve immune system
2 - patients have monoclonal antibodies made for them
3 - patients are given a mixture of antibodies (typically IgG and IgM)
4 - all of the above

Answer 18

3 - patients are given a mixture of antibodies (typically IgG and IgM)
- similar to a blood transfusion

• Anaphylaxis (IgA deficiency, small risk)
• Mostly immunomodulatory
• Highly viscous
• Prothrombotic especially VTE

Question 19

Patients with myasthenia gravis can be given plasmapheresis as part of immuno modulation. What is plasmapheresis as a treatment?

1 - patients are vaccinated to improve immune system
2 - patients have monoclonal antibodies made for them
3 - patients are given a mixture of antibodies (typically IgG and IgM)
4 - patients own antibodies are taken out and replaced with blood products

Answer 19

4 - patients own antibodies are taken out and replaced with blood products

• removes plasma and blood products, specifically the antibodies that are attacking ACh receptors
• need to monitor coagulation factors as these can be lost in this process

Question 20

If a patient has a thymoma, can a thyroidectomy have any beneficial effect?

Answer 20

• yes
• has shown benefits of reducing muscke weakness even in patients without a thymoma
• potentially linked with reduced T cell production so less cytotoxic T cells