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Disease 2 > Myasthenia Gravis > Flashcards

Myasthenia Gravis Flashcards

1
Q

Define myasthenia gravis

A

An autoimmune neuromuscular disorder characterized by fluctuating motor weakness involving ocular, bulbar, limb and respiratory muscles

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2
Q

What effect can impairment of the bulbar nerves cause?

A

Dysphagia
Reduced gag reflex
Slurred speech
Aspiration of secretions
Impaired cough

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3
Q

What is the weakness associated with MG caused by?

A

An immunological attack on the post synaptic membrane where acetylcholine receptors are located

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4
Q

What is the most common disorder of neuromuscular transmission?

A

Myasthenia gravis

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5
Q

How does MG block neuromuscular impulses?

A

Antibodies attack nicotonic receptors preventing them from binding with acetylcholine

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6
Q

What is a characteristic of the weakness associated with MG?

A

Improves after rest

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7
Q

Are the eyes affected equally in MG?

A

Not necessarily

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8
Q

Describe ocular MG

A

Muscle weakness limited to eyes and extraocular muscles

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9
Q

Describe generalized MG

A

Variable muscle weakness in bulbar muscles, limbs, and respiratory muscles

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10
Q

How may a patient with generalized MG present?

A

Drooped head
Expressionless
Ptosis
Diplopia Double vision
Slurred speech (dysarthria)

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11
Q

How is MG a respiratory problem?

A

May cause weakness of the respiratory muscles which can lead to respiratory insufficiency or failure

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12
Q

What antibody is responsible for the neuromuscular weakness seen in MG?

A

IgG

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13
Q

How does IgG disrupt the transmission of acetylcholine?

A

Not well understood
May block receptor sites
Destroy receptor sites
Accelerate breakdown of acetylcholine

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14
Q

What kind of motion is more susceptible to the weakness associated with MG?

A

Repetitive

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15
Q

What patients would raise a suspicion of MG?

A

Patients with fatigable muscle weakness
Patient w isolated ptosis (drooping eyelid) and/or diplopia (double vision)

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16
Q

Describe how the icebag test works on patients with MG

A

Neuromuscular transmission improves at lower temperatures so cooling the eyelids allows for improved function IF the dysfunction is due to impaired neuromuscular transmission

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17
Q

What is a pharmacological test for MG?

A

Edrophonium (tensilon) test

18
Q

What does the edrophonium or tensilon test do?

A

Short acting drug that inhibits acetylcholinesterase from functioning allowing for higher concentrations of acetylcholine and increases signal transmission

19
Q

Why does steve hate edrophonium?

A

Its not used in US
Supposedly unreliable
Associated with adverse events

20
Q

What is serologic testing?

A

Testing for antibodies to acetylcholine receptors

21
Q

If a patient is seropositive, what antibodies are present?

A

AChR
MuSK

22
Q

What does it mean if a patient is seronegative?

A

It means theyh dont have the AChR or MuSK antibodies and will need further testing

23
Q

How many patients with generalized MG are seronegative?

A

90%

24
Q

What are the 3 electrodiagnostic studies used for MG?

A

Nerve conduction
Electromyography
Single fiber electromyography

25
Q

Describe repetitive nerve stimulation testing for MG

A

Stimulate motor nerve of a selected muscle 6-10 times at low rates and observe for changes ins compound muscle action potential (CAMP) amplitude

26
Q

What constitutes a positive result from a repetitive nerve stimulation test for MG?

A

Progressive decline in CAMP amplitude after 4-5 stimuli
>10% decrease required for a positive test

27
Q

What is the most sensitive test available for MG?

A

Single fiber electromyography (SFEMG)

28
Q

Describe single fiber electromyography (SFEMG)

A

A special needle electrode allows simultaneous recording of action potential of two muscle fibers innervated by the same motor neurons

29
Q

What constitutes a positive test with the single fiber electromyography test?

A

When the muscle is stimulated, the second fiber will falter behind the first, causing a jitter that is measurable

30
Q

Why should the thymus be investigated when considering MG?

A

Thymus creates antibodies
A thymoma or thymic mass may be causing the thymus to create bad antibodies

31
Q

What kind of lung pathology is associated with MG?

A

Restrictive lung pathology
Decreased flows
Decreased volumes
Decreased capacities

32
Q

What is an ABG of someone with MG likely to look like?

A

Respiratory acidosis

33
Q

How will the CXR of a patient with MG look?

A

Normal

34
Q

How are patients with MG managed in the hospital?

A

Repeated NIF + VC to assess need for intubation
SpO2
ABGs

35
Q

When is a patient with MG considered to be in respiratory failure?

A

RR > 30
SpO2 < 92
FVC < 20 (or 30% reduction since last measurement)
NIF < 30
MEP < 40
PaCO2 > 50

36
Q

What are the 4 main treatment pathways for MG?

A

Acetylcholinesterase inhibition
Immunosuppressive or immunomodulatory agents
Short acting immunomodulating agents
Thymectomy

37
Q

What medication is used to inhibit acetylcholinesterase?

A

Pyridostigmine (mestinon)

38
Q

When is pyridostigmine (mestinon) used?

A

Mild cases
Less effective in severe cases

39
Q

What drugs can be used on patients who do not tolerate acetylcholinesterase inhibitors?

A

Glucocorticoids

40
Q

What treatments are used as a rapid response to a myasthenic crisis?

A

PLEX
IVIG

41
Q

What are options for chronic management of MG?

A

Avoid medications that may exacerbate MG
Seek vaccinations

Disease 2 (16 decks)

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