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Year Two - Neurology System > Myasthenia Gravis > Flashcards

Myasthenia Gravis Flashcards

1
Q

What is myasthenia gravis?

A

It is an autoimmune condition, in which there is antibody formation against post-synaptic nicotinic acetylcholine receptors of the neuromuscular junction

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2
Q

What generally occurs at the neuromuscular junction?

A

There is communication of motor nerves with muscles

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3
Q

Describe the process that occurs at the neuromuscular junction that leads to muscular contraction

A

The axons of the motor nerves are situated across a synapse from the post-synaptic membrane of the muscle cell

The axons release a neurotransmitter, known as acetylcholine, from the pre-synaptic membrane which then travels across the synapse and attaches to the receptors on the post-synaptic membrane

This causes receptor stimulation, leading to muscle contraction

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4
Q

What is the pathophysiology of myasthenia gravis?

A

There are acetylcholine receptor antibodies are produced by the immune system

These antibodies bind to the postsynaptic neuromuscular junction receptors, preventing the binding of acetylcholine and therefore muscle contraction

During muscle activity, there is a gradual increase in receptor inhibition, resulting in progressive muscle weakness during periods of activity and gradual improvement during periods of rest

These antibodies also activate the complement system within the neuromuscular junction, leading to damage to cells at the postsynaptic membrane

This causes further worsening of clinical features

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5
Q

What two other antibodies are associated with myasthenia gravis?

A

Muscle-specific kinase (MuSK) antibodies

Low-density lipoprotein receptor-related protein 4 (LRP4) antibodies

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6
Q

What is the function of MuSK and LRP4?

A

They are proteins involved in the production and formation of the acetylcholine receptors

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7
Q

How does MuSK and LRP4 antibody formation lead to myasthenia gravis?

A

The destruction of these proteins results in inadequate acetylcholine receptor formation

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8
Q

What are the six risk factors of myasthenia gravis?

A

Females < 40 Years Old

Males > 60 Years Old

Thymomas

Thymic Hyperplasia

Autoimmune Disorders

Drug Administration

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9
Q

What are thymomas?

A

Tumours of the thymus gland

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10
Q

What four autoimmune disorders are associated with myasthenia gravis?

A

Pernicious anaemia

Autoimmune thyroid disorders

Rheumatoid arthritis

Systemic Lupus Erythematosus

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11
Q

What are ten drugs are associated with myasthenia gravis?

A

Penicillamine

Quinidine

Procainamide

Beta-Blockers

Lithium

Phenytoin

Gentamicin

Macrolides

Quinolones

Tetracyclines

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12
Q

What is the characteristic clinical feature of myasthenia gravis?

A

Muscle fatiguability

This is when muscles become progressively weaker during periods of activity and slowly improve after periods of rest

This usually means that clinical features are minimal in the morning and worse at the end of the day

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13
Q

What are the five clinical features of myasthenia gravis?

A

Diplopia

Ptosis

Facial Muscle Weakness

Dysphagia

Slurred Speech

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14
Q

What muscle weakness causes diplopia?

A

Extra-ocular muscle weakness

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15
Q

What muscle weakness causes ptosis?

A

Eyelid muscle weakness

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16
Q

In what three ways can we elicit muscle fatiguability during clinical examination?

A

We can ask the patients to repeatedly blink, which will exacerbate ptosis

We can ask the patients to prolong upward gazing, which will exacerbate diplopia on further eye movement testing

We can ask the patients to repeat unilateral arm abduction, which will exacerbate unilateral weakness when comparing both sides

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17
Q

What four investigations can be used to diagnose myasthenia gravis?

A

Blood Tests

Electromyography (EMG)

CT Scans

Edrophonium Test

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18
Q

What is the first line investigation of myasthenia gravis?

A

Blood tests

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19
Q

What four blood test results indicate myasthenia gravis?

A

Increased Acetylcholine Receptor (Ach-R) Antibodies

Increased Muscle-Specific Kinase Antibodies (MuSK) Antibodies

Increased Low-Density Lipoprotein Receptor-Related (LPR4) Antibodies

Normal Creatinine Kinase Levels

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20
Q

What is electromyography (EMG)?

A

It measures muscle response or electrical activity in response to a nerve’s stimulation of the muscle

21
Q

What are the two features of myasthenia gravis on EMG?

A

Decremental Response To Repetitive Nerve Stimulation

Single-Fibre Jitter

22
Q

How are CT scans used to investigate myasthenia gravis?

A

They can detect underlying causes, such as thymomas

23
Q

What is a feature of myasthenia gravis on CT scans?

A

Anterior Mediastinum Mass

24
Q

What is another term for the edrophonium test?

A

Tensilon test

25
Q

What is the edrophonium test?

A

It involves administrating an IV dose of edrophonium chloride

26
Q

What is the function of edrophonium?

A

It is an acetylcholinesterase inhibitor, which means that it inhibits cholinesterase enzymes in the neuromuscular junction – an enzyme involved in the break down acetylcholine

This means that it increases acetylcholine levels at the neuromuscular junction

27
Q

What edrophonium test result indicates myasthenia gravis?

A

Once edrophonium has been administered, there should be temporary relief of muscle weaknes

28
Q

Why is the edrophonium test only reserved for when myasthenia gravis diagnosis is unclear?

A

This is due to the risk of cardiac arrythmia

29
Q

What are the three pharmacological management options for myasthenia gravis?

A

Long Acting Acetylcholinesterase Inhibitors

Immunosuppressants

Monoclonal Antibodies

30
Q

Name two long acting acetylcholinesterase inhibitors used to treat myasthenia gravis

A

Pyridostigmine

Neostigmine

31
Q

What is the first line long acting acetylcholinesterase inhibitor?

A

Pyridostigmine

32
Q

What is the function of long acting acetylcholinesterase inhibitors?

A

They increase the level of acetylcholine in the neuromuscular junction

33
Q

How are long acting acetylcholinesterase inhibitors used to treat myasthenia gravis?

A

They provide symptomatic relief

34
Q

Name four immunosuppressants used to treat myasthenia gravis

A

Prednisolone

Azathioprine

Cyclosporine

Mycophenolate mofetil

35
Q

How are immunosuppressants used to treat myasthenia gravis?

A

They can be added to long acting acetylcholinesterase inhibitors to suppress the production of antibodies

36
Q

Name two monoclonal antibodies used to treat myasthenia gravis

A

Rituximab

Eculizumab

37
Q

What is the function of rituximab? How is it therefore used to treat myasthenia gravis?

A

They target B cells

They reduce the production of antibodies

38
Q

What is the function of eculizumab? How is it therefore used to treat myasthenia gravis?

A

They target complement protein C5

This could potentially prevent the complement activation and destruction of acetylcholine receptors

39
Q

What surgery can be used to manage myasthenia gravis?

A

Thymectomy

40
Q

What is thymectomy?

A

It involves resection of the thymus gland

41
Q

How is thymectomy used to treat myasthenia gravis?

A

It can be used to provide symptomatic relief in individuals with and without a thymoma

42
Q

What is a complication of myasthenia gravis?

A

Myasthenic Crisis

43
Q

What is myasthenic crisis?

A

It is a life-threatening complication, in which there is an acute worsening of clinical features due to another illness

44
Q

What illness commonly triggers myasthenic crisis?

A

Respiratory tract infection

45
Q

What clinical feature is typical of myasthenic crisis? Why?

A

Respiratory failure

There is weakness of respiration muscles

46
Q

How do we manage respiratory failure in myasthenic crisis?

A

Non-invasive ventilation with BiPAP

OR

Full intubation and ventilation

47
Q

What two pharmacological management options can be used in myasthenic crisis?

A

IV immunoglobulins

Plasmapheresis

48
Q

What is plasmapheresis?

A

Plasma exchange

Year Two - Neurology System (25 decks)

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