BS - Eye Muscle Disorders - Week 4

Question 1

Name 2 types of EM disorder causes and give three causes for each type.

Answer 1

Neural causes

• abnormal control - brain centres
• bad neural connections - cranial nerve/pathways

Muscular/mechanical causes

• muscle insertions (tropia/phoria)
• orbital congestion
• muscle capacity

Question 2

Give two examples of an inflammatory orbital congestion disorder.

Answer 2

Grave’s disease

Thyroid eye disease

Question 3

Give two examples of neuromuscular junction disorders.

Answer 3

Myasthenia gravis

Myotonic dystrophy

Question 4

Give an example of an inherited neuropathy affecting the EOM, and describe how its transmitted.

Answer 4

Lebers syndrome, a mitochondrial disorder.

Question 5

What is the difference between thyroid eye disease and Graves disease (5)?

Answer 5

Graves disease is an endocrine disorder and the primary insult in in the thyroid. It may or may not express eye disease

Thyroid eye disease - primary insult in ocular, with normal thyroid function euthyroid.

Question 6

Does Graves disease always cause eye disease?

Answer 6

No

Question 7

What can be said of the inflammation grade of thyroid eye disease clinically (2)?

Answer 7

It is low grade, and might be early or preclinical Graves disease.

Question 8

What is thyroid eye disease caused by?

Answer 8

Aberrant immune response

Question 9

What is thyroid eye disease secondary to?

Answer 9

Hyperthyroidism

Question 10

What does the hypothalamus sense, and what does it release in response?

Answer 10

Senses low T3/T4 in blood, and releases thyroid regulating hormone - TSH.

Question 11

What does the anterior pituitary gland release, and what stimulates it?

Answer 11

TRH stimulates the APG to release thyroid stimulating hormone - TSH

Question 12

What does the thyroid gland release, and what is it stimulated by?

Answer 12

Released thyroglobulin TGB, stimulated by TSH.

Question 13

What happens to thyroglobulin?

Answer 13

Becomes T3/T4

Question 14

What does T3/T4 do?

Answer 14

Gives feedback to the pituitary and hypothalamus.

Question 15

Which is the only endocrine gland to store its own secretion, and what does it store?

Answer 15

Thyroid gland, storing TGB

Question 16

Stimulation of which cells results in the production of TGB?

Answer 16

Follicular cells of the thyroid

Question 17

What do parafollicular cells produce, and what does it do?

Answer 17

Calcitonin, inhibiting osteoclasts

Question 18

What 7 actions does the thyroid have on the body?

Answer 18

Increases heart rate
Increases glucose turnover
Increases body temperature
Increases Na+/K+-ATPase synthesis
Increases protein synthesis
Increases lipolysis
Increases bone turnover

Question 19

Describe the mechanism of Graves disease (5).

Answer 19

Antibodies (long standing thyroid stimulators) directed against thyrotropin receptors found on the endothelial surface of thyroid follicular cells, mimicing the action of TSH, but not subject to normal feedback.

Question 20

Name two hypotheses for the cause of Graves disease.

Answer 20

Genetic tendency (lack of T-cell suppression)
or
Prior exposure to gut bacteria which have receptors on their cell membranes with homology to TSH-receptors, giving rise to antibodies agonistic to TSH-receptors, overstimulating them

Question 21

The development of Graves disease requires the participation of which cell?

Answer 21

Self-reactive helper CD4+ T-cells, producing an antibody mediated autoimmune response

Question 22

Name 5 ocular manifestations of Graves disease.

Answer 22

Lid retraction
Lid lag
Proptosis
Extraocular muscle involvement
Optic nerve dysfunction

Question 23

What is the age of onset for Graves disease in men and women?
What is the risk for smokers?

Answer 23

Women - 20-40s
Med 50-60s
Smokers at 2x risk

Question 24

Name some general systemic symptoms of Graves disease.

Answer 24

Anxiety, irritability, insomnia, irregular hear beat, fine tremor of hands/fingers, increased perspiration, heat sensitivity, weight loss but normal food intake, brittle hair, goitre, light to no menstruation, frequent bowel movements

Question 25

Name two demopathies of graves disease.

Answer 25

Local swellings of feet and lower legs, altered colour and itch.

Question 26

Name 4 histopathologies of thyroid eye disease.

Answer 26

Increased orbital fat content
EOM swelling
Increased fibrosis and GAG synthesis - swelling pressure
Inflammatory cell infiltration of the EOM - muscular fibrosis

Question 27

List the clinical expression types of thyroid eye disease, and percentage for each.

Answer 27

80% hyperthyroid

20% euthyroid

Question 28

What kind of disease is myasthenia gravis, what is affected, and how?

Answer 28

Autoimmune disorder causing weakness of skeletal muscles due to antibodies formed against nicotinic receptors

Question 29

List three ocular manifestations of myasthenia gravis.

Answer 29

Ptosis
Diplopia (often vertical)
Fatigue on repeated effort (+10x)

Question 30

Briefly describe the neuromuscular junction mechanisms.

Answer 30

Ach released from the nerve terminal following the action potential.
Move across the synaptic cleft to Ach receptors on the post-synaptic membrane.
Ach-esterase on the post-synaptic cleft scavenges and hydrolyses unbound Ach.

Question 31

Describe the role of IgG in myasthenia gravis (3), and what happens in advanced cases (4).

Answer 31

IgG is an agonist of nAChR, and binds at the neuromuscular junction, blocking receptor activation of Ach.
Advanced - complement C9 colocalises with IgG on nAchR, internalising, disrupting and destroying nAchRs.

Question 32

What population is most affected by myasthenia gravis?

Answer 32

Young women and older men

Question 33

What is myasthenic crisis?

Answer 33

Complete loss of breathing capacity

Question 34

Does thyroid/thymus dysfunction occur in those with myasthenia gravis?

Answer 34

Yes, in 5-15%.

Question 35

Describe the action and purpose of tensilon/edrophorium chloride testing.

Answer 35

A short acting Ach-esterase that prolongs Ach action.
Intravenous gives transient improvement to muscle strength.
Clinically, improvement to ptosis.

Question 36

Describe the single fibre electromyography test, and what it is for.

Answer 36

For testing myasthenia gravis.
Concentric needle electrode is inserted into the muscle to allow identification of action potentials from individual muscle fibres.
Jitter is seen in 95-995 of patients with myasthenia gravis.

Question 37

Describe myotonic dystrophy, and how it is genetically transmitted.

Answer 37

Autosomal dominant condition that leads to myotonia - the inability to relax muscles.

Question 38

Genetically, myotonic dystrophy is similar to what other disease?

Answer 38

Huntington disease.

Question 39

What is the onset of myotonic dystrophy, and death?

Answer 39

Onset - 20-30s

Death - by 50s

Question 40

Do individuals with myotonic dystrophy experience endocrine dysfunction?

Answer 40

Yes, its common due to epithelial dystrophy, especially testicular, leading to baldness.

Question 41

List 7 ocular manifestations of myotonic dystrophy.

Answer 41

Ptosis
Fatigue
Cataracts
Pigment epithelial dystrophy
Retinal degeneration
Ciliary body dysfunction
Reduced IOP