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OD3 - Clinical Optometry Practice > NV - Neuromuscular Disorders II: Myasthenia Gravis - Week 2 > Flashcards

NV - Neuromuscular Disorders II: Myasthenia Gravis - Week 2 Flashcards

1
Q

Recap: what test detects proptosis? What test measures it? What does scleral show indicate and what is checking for lid lag on down gaze helpful for?

A

Birds eye - detection
Side view - measurement
Scleral show can indicate proptosis
Lid lag on downgaze is helpful for diagnosis

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2
Q

How can you tell whether ocular misalignment is comitant or incomitant? What List a cause for both of these.

A

Comitant - decompensated congenital deviation

Incomitant - CN4 palsy or acquired

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3
Q

List three acquired causes of incomitant ocular misalignment.

A

Paretic
Mechanical (TED)
Neuromuscular

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4
Q

What kind of disorder is myasthenia gravis?

A

Autoimmune disorder

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5
Q

Antibodies against what is produced in myasthenia gravis? Describe what this causes and how this affects receptor binding, number, and activation.

A

Nicotinic acetylcholine receptors (nAchR)
Local membrane internalisation increases
-internalised nAchR does not bind as readily
Receptor numbers decrease and activation decreases

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6
Q

What are two expressions of myasthenia gravis (3)?

A

Systemic
Ocular
Both

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7
Q

What percentage of myasthenia gravis patients have only ocular problems? What is this known as? What Percentage of myasthenia gravis patients with only ocular problems develop systemic problems and within what timeframe?

A

40% of all MG patients have only ocular problems - ocular MG

60-80% of ocular myasthenics develop systemic problems within 2 years of diagnosis

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8
Q

What organ does systemic myasthenia gravis particularly affect?

A

Lungs

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9
Q

What antibody type is produced with myasthenia gravis? What does it do and what happens over time?

A

IgG
Blocks nAChR, they break down with time
-results in decreased number of functional receptors

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10
Q

What additional component co-localises with antibodies in myasthenia gravis and what is the consequence of this (3)? What does this mean for repeated use of the neuromuscular junction?

A

Complement (C9) co-localises with the IgG

  • affects local membranes carrying nAChR
  • nAChRs internalise
  • this speeds the breakdown of nAChRs
  • results in loss of functional nAChRs with use
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11
Q

List the two mechanisms that result in dysfunction of cholinergic receptors in myasthenia gravis and note which one results in fatigability. Describe why.

A 
Antibody IgG mediated
-directed against receptors
Complement C9 mediated
-membrane internalisation
-results in fatigability
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12
Q

Below what percentage of active nAChRs do symptoms of myasthenia gravis begin to manifest?

A

Below 35%

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13
Q

Note two associations of myasthenia gravis. Note the percentage for each.

A

Thymus dysfunction - 70% of MG patients have thymus hyperplasia
Thyroid dysfunction - 5% in MG

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14
Q

What percentage of thyroid dysfunction patients develop myasthenia gravis (male and female)?

A

Male - 9%

Female - 20%

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15
Q

What three ocular signs would you expect to see with myasthenia gravis? Note the most common expression.

A

Ptosis - most common
Vertical diplopia
Fatigue on repeated effort (10-20 times)

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16
Q

Does fatigue from myasthenia gravis improve or worsen with cooling? Explain why (2).

A

Improves

  • cooling acts to stabilise the membrane
  • stops internalisation
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17
Q

List four systemic expressions that may be seen in myasthenia gravis (organs).

A

Face
Tongue
Lungs
With time - ANS (bowels, heart etc)

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18
Q

List two compounds that are used to test for myasthenia gravis. Note what each of these are and how they work.

A

Compounds that increase muscle action with injection:
Neostigmine
-an ACh agonist - slow release of ACh
Tensilon
-an AChE inhibitor - binds to AChE, increasing [ACh] in the synapse

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19
Q

List three ways that fatigability can be exposed with myasthenia gravis.

A

Cogan’s lid twitch (2)
-exaggerated ptosis after repeated/sustained upgaze
-a 2 minute sustained downgaze gives lid twitch on returning to primary gaze
Sleep/ice bag
-sleep/cold improves response
-icepack over muscle for 2-5 minutes

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20
Q

Based on one of the tests for exposing fatigability in myasthenia gravis, when would you expect lid function to be its worst?

A

Afternoon - muscle function improves with sleep

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21
Q

What is the typical age of onset for myasthenia gravis? Is older worse in females or males?

A

30-80

Older is milder in females, worse in males

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22
Q

Why is asymmetric ptosis seen in myasthenia gravis? What percentage of patients will have this?

A

Levator palpebrae superioris involvement (85%)

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23
Q

Involvement of what muscles in myasthenia gravis will gibe nystagmus/diplopia? What percentage of patients will have this?

A

EOM involvement in 5-10% gives nystagmus/diplopia

24
Q

Is the orbicularis commonly or rarely involved in myasthenia gravis? How are the brows normally used by MG patients?

A

It is rarely involved <5%

The brow is often used by MG patients to keep lids open (only when there is no orbicularis involvement)

25
Q

What is a myasthenic crisis and is it an emergency?

A

Respiratory failure resulting in tachycardia

Urgent action needed as it has death potential

26
Q

Describe what herring’s law means for ptotic eyelid and contralateral eyelid function. Describe in what two ways this effect can be eliminated and what it reveals.

A

Levator stimulation in the ptotic eye increases causing grater activation of the contralateral eyelid
Covering the ptotic eye or manually raising the eyelid eliminates overstimulation, allowing the contralateral eyelid to express its true lid position

27
Q

What should you do if ptosis is found in the absence of miosis? What id you have a positive result on this?

A

Check herrings law

-if positive, reconsider MG diagnosis

28
Q

What happens to sympathetic receptors on muscles with peripheral denervation? What about central denervation? What consequence does this have on lid and pupil dilator’s sensitivity to adrenergic agonists? Note which alpha receptor type these two are.

A

Peripheral denervation - causes upregulation of sympathetic receptors on muscles
Central innervation does not
Lid (alpha 2) and pupil dilator (alpha 1) are both supersensitive to adrenergic agonists with peripheral denervation

29
Q

What kind of response would you expect if you use adrenergic drops OU on a case of peripheral Horners and after how long? Name two drugs that can be used and note which of the two alpha receptors they target.

A

Asymmetric response 10-30 minutes after instilling

  • apraclonidine 0.5/1% (alpha 2 > 1)
  • phenylephrine 2.5% (alpha 1 > 2)
30
Q

What should you do if you see pain free Horners syndrome? Is it more likely to be benign or malignant?

A

Check adrenergic suprasensitivity - indicates peripheral horners
-most likely benign

31
Q

What history is indicative of myasthenia gravis?

A

Fatigue worse in the afternoon or repeated use

32
Q

If you confirm myasthenia gravis with lid twitch/ice, what should you do and for what (2)?

A

Refer to GP for DDX

  • CT scan, blood test for antibody assay/thyroid dysfunction
  • tensilon/neostigmine test
33
Q

What is the management for myasthenia gravis (4)?

A

Ptosis crutch (hold eyelid up or surgery)
Medications
Surgery (thymectomy)
Plasmapheresis

34
Q

What does plasmapheresis do?

A

Decreases ACh antibody load

35
Q

List 4 medications available for myasthenia gravis.

A

Mestinon
Steroids (prednisolone)
Cyclosporine
Azathioprine

36
Q

What is lambert-eaton myasthenic syndrome an abnormality of? Is it common or rare? Is it similar to MG? Is it more severe or mild?

A

Ca+ (VGCC) regulation abnormality reduces ACh release at the synaptic cleft
Is rare
Similar but more severe than myasthenia gravis

37
Q

How does botulinum toxin work? Include what it targets specifically.

A

Stops ACh release into the synaptic cleft by degrading SNAP needed for vesicle fusion
Causes major paralysis of muscular activity
Its effects mimic myasthenia gravis but more severe (and both ocular/systemic)

38
Q

What does myotonic dystrophy lead to?

A

Myotonia

-inability to relax muscle contraction

39
Q

What age is myotonic dystrophy expressed? When is death expected?

A

20s to 30s

-death by 50s

40
Q

What is myotonic dystrophy associated with and why? What two other things does it this cause?

A

Associated with endocrine dysfunction

  • due to epithelial dystrophy
  • baldness and testicular dysfunction - male infertility
41
Q

List four ocular changes with myotonic dystrophy.

A

Cataracts (young males)
Pigment epithelial dystrophy
Retinal changes
Ciliary body - reduced IOP

42
Q

What is the cause of myotonic dystrophy?

A

Repeated sequences at chromosome 19

43
Q

Which of the mitocondrial complex proteins can electron leakage occur (3)? List in order of likelihood. What can these electrons bind to and what does it result in the formation of?

A

C1&raquo_space; C3 > C4

Can bind with O2, to give a superoxide, very potent free radical

44
Q

List three ways mitochondrial dysfunction can be expressed. Describe where electron loss occurs in each if applicable (2).

A

Abnormality in mtDNA
Energy deficiency (RPE) and myopathy (C1, ealry complex loss)
Oxidative stress and neuropathy (C4, later complex loss)

45
Q

What is lebers optic neuropathy due to? What kind of complex loss is seen? What does it lead to?

A

Point mutations in mtDNA

-late complex loss leads to advanced neural apoptosis

46
Q

What happens to the disc with lebers optic neuropathy?

A

Normal disc undergoes optic neuroapthy with age (teens to forties)

47
Q

What kind of vision loss would you expect with lebers optic neuropathy?

A

Profound vision loss (6/24 to NLP)

48
Q

What family history would you expect of lebers optic neuropathy?

A

Positive maternal side

49
Q

What are mitochondrial myopathies characterised by on histology?

A

Ragged red fibles

50
Q

What appearance do RPE disorders have? Why does mitochondrial dysfunction often result in them?

A

Salt/pepper appearance

-RPE is high energy tissue

51
Q

What is the onset for chronic progressive external ophthamoplegia?

A

Childhood up to 30s

52
Q

Is the levator palpebrae superioris involved in chronic progressive external ophthamoplegia? Do you see ptosis? List three other ocular signs.

A

Ptosis with no LBS involvement
Ophthalmoplegia
Pigmentary retinopathy (salt/pepper)
Retained lid crease

53
Q

Describe kearns-sayre syndrome (6).

A 
As with chronic progressive external ophthamoplegia with the addition of:
Heart block
Mental retardation
Hearing loss
Endocrine disorder
Cerebellar ataxia
54
Q

What is the onset of mitochondrial encephalomyopathy lactic acidosis stroke (MELAS)? Before what age?

A

Onset in childhood - before 15

55
Q

What kind of vision loss would you expect in MELAS (2)? List four other symptoms.

A

Vision loss as in chronic progressive external ophthamoplegia with the addition of hemianopia
Other symptoms are:
Hemiparesis
Headaches
Convulsions
Short stature due to stroke-like episodes

OD3 - Clinical Optometry Practice (114 decks)

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