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OD1 Semester 2 - Integrated Ophthalmic Sciences and Preclinical Optometry > Muscle Disorders Of The Eye - Week 4 > Flashcards

Muscle Disorders Of The Eye - Week 4 Flashcards

1
Q

List the neural causes of Extraocular Muscle (EM) disorders (3)

A
  • abnormal control: brain/mid-brain centres
  • bad neural connections: cranial nerve & pathways
  • problems at neuromuscular junction
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2
Q

List the muscular/mechanical causes of extraocular muscle disorder (3)

A
  • muscle insertion (tropia/phoria)
  • orbital congestion/swelling: leads to restriction of eye movement
  • muscle capacity: limited due to energy or trauma related limitations (the muscles fatigue and can’t move eyes)
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3
Q

List EOM types and examples

A

Inflammatory orbital congestion
- Graves’ disease

Muscular disease

  • NMJ: innervational problems (NMG, neuromuscular junction)
  • myasthenia graves
  • myotonic dystrophy

Inherited mitochondrial disorders

  • neuropathy: leber’s
  • myopathy: CPEO, MELAS

Muscle capacity

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4
Q

Is Graves’ disease the same as thyroid eye disease (TED)

A

No. People can have graves without having TED and vice versa

Graves can express TED, but not always the case

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5
Q

Explain Graves’ disease: What type of disorder is it? (more specifically than just saying EOM disorder). What does it result in biochemically?

A

Autoimmune endocrine disorder

Involves overactive thyroid gland, leading to increased thyroid hormone production

  • hyperthyroidism, increased blood t3, t4 levels, reduced blood tsh
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6
Q

Where is the primary insult in Graves’ disease? (I.e the primary affected area)

A

Thyroid

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7
Q

Where is the primary insult (affected area) for Thyroid eye disease (TED)? What is thyroid function like? (In TED alone, assume no graves)

A

Primary insult is ‘Ocular’

Thyroid function unaffected/normal (euthyroid)

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8
Q

What is the cause of Thyroid eye disease (TED)?

A

Aberrant immune response (same as Graves)

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9
Q

What links TED with graves?

A

The fact that TED is secondary to hyperthyroidism, a component of graves

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10
Q

What process involved in TED (thyroid eye disease) might suggest early or preclinical Graves’ disease?

A

Low grade inflammation

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11
Q

What does the thyroid gland control? [3]

A
  • uses of energy
  • proteins production
  • how sensitive the body is to other hormones
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12
Q

List the methods of hormonal control:

A

Endocrine: distance control via blood borne hormones

Paracrine: local control of neighbouring cells via ionotropic receptors

Autocrine: self control via a 2nd messenger

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13
Q

Describe endocrine feedback: locations and actions

A
  1. hypothalamus: senses low t3, t4 levels in blood. Releases TRH
  2. Ant. pituitary gland: TRH stimulates secretory cells to release TSH
  3. TSH released into blood stream
  4. Thyroid gland: TSH stimulates prod. of TGB, which becomes t3, t4
  5. t3/t4 released into blood
  6. t3 feeds back to pituitary and hypothalamus

TRH ==> TSH ==> TGB ==> t3/t4 ==> t3 feeds back

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14
Q

Name an EOM disorder that has inflammatory orbital congestion

A

Graves Disease

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15
Q

Name 3 EOM ‘muscular’ disorders

A
  • disorder of NMJ innervation
  • myasthenia gravis
  • myotonic dystrophy
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16
Q

Define neuropathy

A

disease or dysfunction of one or more peripheral nerves, typically causing numbness or weakness

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17
Q

Define myopathy

A

A disease of muscle tissue

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18
Q

Name a neuropathic inherited mitochondrial disorder

A

Leber’s syndrome

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19
Q

Name 2 myopathic inherited mitochondrial disorders

A

CPEO - Chronic progressive external ophthalmoplegia

MELAS - Mitochondrial encephalomyopathy, lactic-acidosis and stroke

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20
Q

What can inaccurate muscle insertion (mechanical EM disorder) result in?

A

When one of the extra-ocular muscles inserts into a slightly different/inaccurate position on an eye, this can cause:

  • misalignment of the eyes (phoria or tropia)
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21
Q

What happens to the thyroid in Graves Disease?

A

Hyperthyroidism - too much thyroid hormone produced

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22
Q

What is Thyrotoxicosis

A

Excess thyroid hormone in body (such that it becomes toxic to your body)

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23
Q

Is Thyroid Eye Disease (TED) associated with hyperthyroidism when it’s the primary insult, or is it only when TED is secondary to Grave’s Disease

A

Can be either. Though is more often when secondary to Grave’s Disease

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24
Q

What 3 glands work together to control how hard the thyroid gland works? What type of control is this?

A

Hypothalamus, Pituitary Gland, and Pineal Gland.

- this is endocrine control

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25
Q

Where is the pituitary gland situated?

A

Just underneath the optic chiasm

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26
Q

How can pituitary gland problems lead to visual field loss?

A

If you have pituitary gland swelling (e.g. pituitary tumour/adenoma), this will press on the optic chiasm, and can injure it.

Type of visual field loss depends on what side of the pituitary gland is swelling (front or back)

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27
Q

How is cAMP important for thyroid hormone production?

A

It produces a pre-cursor to thyroglobulin

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28
Q

How does TSH stimulate the production of TGB (thyroglobulin)?

A

TSH acts on TSH receptor which converts ATP to cAMP, which produces a precursor to TGB, which then turs into TGB

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29
Q

What processes or systems in the body are controlled by thyroid hormones?

A
  • Heart rate
  • glucose/oxygen turn over (therefore ATP production)
  • Body temperature + caloric intake (calories)
  • Na/K-ATPase synthesis
  • Protein synthesis
  • lipid turn over (lipolysis)
  • bone turn over
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30
Q

What effect does increased thyroid hormone (T3, T4) have on lipolysis?

A

Increases lipolysis

31
Q

What effect does increased thyroid hormone have on bone turnover?

A

Increases bone turn over

32
Q

How is thyroid hormone production altered in Grave’s Disease?

A

TS antibodies (TSAb) mimic the action of TSH to activate the TSH receptor. However, these antibodies are NOT subject to negative feedback, so you get this over-production of thyroid hormones

33
Q

What 2 Hypotheses could explain altered thyroid hormone production in Grave’s Disease?

A
  1. Genetic tendency for Grave’s. i.e. lack of T-cell suppression, or
  2. prior exposure to a bacteria with homologically similar receptors to TSH-receptors, resulting in the production of similar antibodies
34
Q

As Grave’s Disease develops, what happens to the production of t-cells? How do they respond?

A

Over-production of Helper T-cells (CD4+) that are self-reactive.

  • this produces an anitbody-mediated autoimmune response
35
Q

Is Grave’s a systemic or local disease?

A

Systemic Disease

36
Q

How often is the eye effected in Grave’s Disease? (the proportion)

A

25-50% of cases

37
Q

What eye related manifestations occur in Grave’s Disease?

A

Lid retraction, lid lag, and proptosis (eye looks like it’s popping out)

Also: EOM involvement or optic nerve dysfunction

38
Q

Can the TSAb antibody in grave’s disease target anything other than the TSH receptors? If so, where? And what does this lead to?

A

These antibodies can target the orbital fat and muscles in the eye. They go to the back of the eye and recruit white blood cells. [local response]

  • This leads to TED
39
Q

Explain how an inflammatory response at the back of the eye proceeds.

A
  • T-cell infiltration produces inflammatory cytokines
  • Excessive ECM production
  • Proliferation of adipocytes produce fat
  • Tissue and muscle swelling
40
Q

At what age and form does grave’s disease manifest in women?

A

Ages 20-40. Mild form

41
Q

At what age and form does grave’s disease manifest in men?

A

Ages 50-60. Severe form

42
Q

What proportion of grave’s disease patients are male vs female?

A

Male: 35%
Female: 65%

  • more frequent in females
43
Q

How does smoking affect the risk of Grave’s Disease?

A

Doubles the risk

44
Q

List 4 possible systemic symptoms of Grave’s Disease [note: there are many more]

A
  • anxiety, irritability, insomnia, irregular heart beat, frequent bowel movements
45
Q

What changes to your skin might occur in Grave’s Disease?

A

local swellings of feet, lower legs (altered colour, itch)

46
Q

What might be the consequences of EOM swelling?

A
  • eye gets pushed forward: proptosis
  • diplopia
  • squashing of optic nerve (therefor damage)
47
Q

How might EOM swelling impact IOP levels?

A

Increase IOP, which can then add to nerve damage

48
Q

What major histopathological changes can TED result in?

A
  • increased fat content of orbit (upper)
  • swelling of EOMs (upper)
  • Increased fibrosis and GAG synthesis in connective tissue of orbit
  • presence of inflammatory cells in EOM (mainly CD4+ and CD8+)
49
Q

What techniques can you use for the early diagnosis of TED?

A
  • MRI

- OCT

50
Q

What proportion of TED patients have hyperthyroid vs normal (euthyroid)?

A

80% hyperthyroid

20% euthyroid

51
Q

What type of clinical signs can develop in TED?

A
  • orbital congestion: local rigidity gives proptosis
  • chemosis: swelling fluid retention
  • inflammation: redness
52
Q

Describe what happens in orbital congestion

A

Blood flows into the orbit, but at high pressure, the veins will get crushed and so the blood can’t flow out and gets trapped – so the tissue swells and looks really red

53
Q

What gene mutations have been implicated int he development of TED?

A

Cytokien genes: assoc. with imbalance of pro-inflammatory cytokine production

HLA gene: assoc. with autoreactivity

CTLA-4 gene: disturbance in T-cell suppression

Note: these genes are genes that are related to increased chance of having inflammation [that’s really the take-home message]

54
Q

What type of EOM disorder is Myaesthenia Gravis?

A

Muscular, auto-immune.

55
Q

How does Myaesthenia Gravis affect muscles?

A

Leads to weakness of skeletal muscles

56
Q

Describe the autoimmune reactivity in Myaesthenia Gravis?

A

antibodies form against nicotinic acetylcholine receptors

57
Q

Where can systemic manifestations for Myaesthenia Gravis occur?

A

In the lungs

58
Q

What percentage of ocular myaesthenics develop systemic problems in less than 2 years?

A

60-80%

59
Q

List 3 clinical symptoms of myaesthenia gravis

A
  • lid ptosis
  • diplopia (often vertical)
  • fatigue on repeated effort (e.g. more ptosis after blinking many times in a row)
60
Q

When do myaesthenia gravis patients experience the LEAST amount of lid ptosis?

A

In the morning, when the muscles are less fatigued

61
Q

What is IgG and what does it do?

A

IgG is an agonist for the acetylcholine receptor (nAChR). It blocks receptor activation by ACh.

62
Q

Where does IgG bind?

A

At the neuromuscular junction (NMJ)

63
Q

What type of people get myaesthenia gravis?

A

young women and old men

64
Q

Where/How does myaesthenia gravis express?

A

in EM, arms, legs, breathing, swallowing

65
Q

Define Myasthenic Crisis

A

Complete loss of breathing capacity (px requires artificial ventilation)

66
Q

What percentage of myaesthenia gravis cases have thyroid/thymus dysfunction? Can this be resolved?

A

5-15%. Px can have thymectomy (remove thyroid gland), which leads to resolution in some people

67
Q

What clinical tests can we use to test for myesthenia gravis?

A

Tensilon/edrophonium chloride testing

or

Single Fibre Electromyography (SFEMG)

68
Q

How does Tensilon/edrophonium chloride testing work?

A
  • inject a short acting acetyl-cholinesterase inhibitor that prolongs the action of ACh in NMJ, meaning there is now more ACh to compete with the IgG
  • should transiently improve muscle strength
  • Observe if this improved ptosis
69
Q

What effect might an ice-pack have on lid ptosis?

A

Improves it

70
Q

What would SFEMG (single fibre electromyography) find for patients with myaesthenia gravis?

A

Abnormal muscle fibre jitter in 95-99% of cases

71
Q

What type of mendelian inheritance is Myotonic dystrophy? What age onset?

A

Autosomal dominant. Occurs due to repeated sequence of 3’ nucleotides. 20s-30s yr old

72
Q

What does myotonic dystrophy lead to?

A

Myotonia, inability to relax muscle

73
Q

How is myotonic dystrophy expressed?

A

as a multi-system disorder. Expressed in several forms (DM1-DM4)

74
Q

What are the ocular manifestations of myotonic dystrophy, and in what form are they most prominent in?

A

Most prominent in DM1.

  • ptosis and fatigue
  • cataracts
  • pigment epithelium dystrophy
  • retinal degeneration
  • ciliary body dysfunction

OD1 Semester 2 - Integrated Ophthalmic Sciences and Preclinical Optometry (49 decks)

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