Thyroid Tutorials Flashcards
1
Q
what are thyroid follicles
A
balls of epithelial cells surrounding proteinaceous (non cellular) colloid
2
Q
where are thyroid hormones stored
A
in colloid
3
Q
how is T3 produced
A
de-iodination of T4 within target cells outside the thyroid
4
Q
what do thyroid hormones bind to
A
serum proteins- thyroid binding globulin
5
Q
what enzyme activates iodine
A
a peroxidase enzyme
6
Q
how is tyrosine involved in thyroid hormones
A
tyrosine residues on thyroglobulin are iodinated forming MIT and DIT which couple together to form T4 and T3
7
Q
what is thyroglobulin
A
protein made by thyroid cells
8
Q
how are thyroid hormones secreted
A
colloid is resorbed into the thryoid cells by endocytosis
thyroglobulin is broken down by lysosomes to release (T4 and some T3)
secreted into blood stream
9
Q
what stimulated the thyroid to produce thyroid hormones
A
TSH secreted by the pituitary
10
Q
what is thyrotropin
A
thyroid stimulating hormone
11
Q
what are the types of goitre
A
diffuse and nodular
12
Q
what are the 7 causes of goitres
A
iodine deficiency multinodular goitre graves disease thyroiditis tumour cysts inherited (abnormality of enzyme pathway or T4 receptor)
13
Q
what can cause thyroiditis
A
(thyroiditis is an inflammatory response) hashimotos (autoimmune) subacute causes (de Quervains, viral) acute causes (bacterial) drugs (lithium, amiodarone)
14
Q
what are the usual features of a malignant thryoid nodule
A
<20 and >70 years old male dysphagia/ dysphonia previous neck irradiation firm, hard, immobile cervical lymphadenopathy
15
Q
what are usual features of a benign thyroid nodules
A
FHX of autoimmune diseases FHX benign nodules/ goitre associated hormone disturbances pain/ tenderness soft, smooth, mobile
16
Q
how should thyroid lumps over 1.5 cm be investigated
A
ultrasound and fine needle aspirate (under ultrasound guidance)
17
Q
what is a thyroid isotope scan useful for
A
establishing the cause of thyrotoxicosis- can identify multinodular goitres, toxic adenomas and thyroiditis
18
Q
what antibodies can you check for in thyroid disease
A
anti TPO (thyroid peroxidase)
anti-thyroglobulin
TSH receptor antibody (TRAB)
19
Q
what do thyroid function tests show in primary hypothyroidism
A
increased TSH
decreased T4/T3
20
Q
what do thyroid function tests show in secondary hypothyroidism
A
decreased TSH
decreased T4/3
21
Q
what do thyroid function tests show in hyperthyroidism
A
decreased TSH
increased T4/3
22
Q
what do thyroid function tests show in subclinical hyperthryoidism
A
decreased TSH
normal T3/4
23
Q
what do thyroid function tests show in sick euthyroid
A
normal or decreased TSH
decreased T4/3
24
Q
what are the symptoms of hyperthyroidism
A
nervous, anxious, irritable warm, sweaty, heat intolerance tachycardia, palpitations, weight loss, increased appetite (10% have weight gain), diarrhoea, amenorrhoea, weakness, fatigue
25
what are the causes of hyperthyroidism
```
autoimmune (graves)
multinodular goitre
toxic solitary nodule
thyroiditis
exogenous thyroid hormones
thyroid cancer
hydatiform mole
TSH secreting pituitary tumour
```
26
what is a thyroid storm
CRISIS
untreated/ inadequately treated thyrotoxicosis + preciptating factors (MI, infection, PE)
rare but life threatening - medical emergency
27
what are the features of a thryoid storm
```
HR increased
BP decreased
fever
altered mental status
multiorgan failure
```
28
how do you manage a thyroid crisis
```
carbimazole (high dose)
beta blockers
hydrocortisone
potassium iodide
IV fluids +/- inotropes
treat precipitating cause (MI, infection, PE)
```
29
what are the signs associated with graves
dysthyroid eye disease
thryoid acropathy
pretibial myxoedema
30
what are the forms of dysthyroid eye disease
swelling of extra ocular muscles, lymphocytic infiltration, late fibrosis and muscle tethering.
causes:
- proptosis (eye protusion)
- lid lag
- opthalmoplegia (swelling of muscles causing orbital muscle paralysis - can present as diplopia)
31
describe thyroid acropachy
oft tissue swelling and periostial bone changes
32
what can worsen graves opthalmology
smoking and hypothyroidism
33
what are the clinical features of dysthyroid eye disease
```
grittiness, watery eyes, conjunctival injection,
eyelid retraction,
proptosis,
visual blurring,
painful eye movements
```
34
what are the primary causes of hypothyroidism
autoimmune- hasimotos/ postpartum
iatrogenic- post surgery or radioiodine
other- excess iodine, iodine deficiency and goitrogens (lithium etc.), inborn errors of thyroid hormone synthesis
35
what are the secondary causes of hypothyroidism
pituitary or hypothalamic disease
36
what other than primary and secondary causes of hypothyoridism can cause hypothyroidism
peripheral resistance to thyroid hormone
37
what is the treatment for hypothyroidism
levothyroxine (T4)
- start at 50 or 200 micrograms (lower if IHD or LVF)
liothyronine (T3)
-start at 20 micrograms
38
what are the symptoms of hypothyroidism
```
fatigue
lethargy
cold intolerance
weight gain
dry puffy skin
hair loss
constipation
menorrhagia
muscle weakness
bradycardia
```
39
what is the ultrasound classification for ultrasound thryoid cancers
U1-2 benign
U3- indeterminate
U4-5 malignant
40
what are 80% of all thyroid cancers
papillary cell carcinomas
41
what would been seen in thyroid tests for a goitre caused by menopause
suppressed TSH and raised T4
42
what is pemburtons sign
used to evaluate venous obstruction in patients with goiters. The sign is positive when bilateral arm elevation causes facial plethora
43
why do anti thyroid drugs take 3-4 weeks minimum to work
as stores of thyroid hormones
44
what should you be careful of when on antithyroid drugs
agranulocytosis- suppression of bone marrow, be aware of any sore throat or mouth ulcers
45
what changes should be made in thyrotoxicosis during pregnancy
switch carbimazole to propylthiouracil for first trimester then back in second
thyrotoxicosis very bad for feotus, make sure its well controlled
46
if a patient is non compliant to thyrotoxicosis meds what are their treatment options
radio iodine, sugery
47
what will probably happen eventually after radio iodine
will develop hypothyroidism, be on lifelong thyroxine
48
what antibodies for hypothryoidism
Anti-thyroid peroxidase (anti-TPO) antibodies or anti-thyroglobulin antibodies are found in 90-95% of patients with autoimmune thyroiditis
49
what antibodies for hyperthyroidism
Antimicrosomal antibodies - against thyroid peroxidase. Thyroid peroxidase antibodies are present in about 75% of cases of Graves
Antithyroglobulin antibodies
TSH-receptor antibodies (very specific and sensitive for graves)
50
what is the most common cause of hypopituitarism
a pituitary tumour
51
why does the thyroid move on swallowing
as it is attached to the upper end of the trachea
52
what cell types make up the thyroid
follicular cells (encase colloid) and parafollicular cells (lie within connective tissue)
53
what cell type produces thyroglobulin
follicular
54
what cell type produces calcitonin
parafollicular C cells
55
where is thyroglobulin stored
in the colloid
56
what is pinocytosis
occurs at colloid, causes the release of thyroglobulin
57
what acts on thyroglobulin to make thyroid hormones
lysosomes
58
how is iodine involved in thyroid hormones
enters from bloodstream in follicles
attached to the tyrosine residues on thyroglobulin to form MIT and DIT
T3= 2 x MIT
T4= MIT + DIT
59
where are T3 and T4 stored
in colloid thyroglobulin
60
what is the majority of secreted thyroid hormone
T4 (triiodothyronine)
61
where is T4 converted to T3
liver and kidneys
62
are T3 and T4 hydrophilic or phobic
phobic
calcitonin is phillic
63
what effects does thyroid hormone have on metabolism
increases protein synthesis, glucose and fatty acid plasma levels, thermogenesis, bone turnover and gut motility
64
what effect does growth hormone have on fat tissues
increases lipolysis, increasing plasma fatty acids
65
what effect does growth hormone have on the liver
increases gluconeogenesis, increasing plasma glucose
66
what effect does growth hormone have on muscle
increases protein synthesis, decreasing plasma amino acids
67
how does thyroid hormone affect fat storage
decreases it
68
what is the role of thyroid hormone in the nervous system
increase responsiveness to neurotransmitters - increases the numbers of receptors to these transmitters (e.g. adrenaline and noradrenaline)
69
what regulates thyroid hormone
TRH (from hypothalamus, acts on ant pituitary) and TSH (ant pituitary, acts on thyroid gland) positive feedback
T3 negatibe feedback on ant pituitary and hypothalamus
70
what hormone will always be raised in graves
T4 (T3 may be high or normal)
71
what complications are specific to graves disease
exopthalamus- loss of eye movement, feels gritty, eye pushed forward, blurred vision, eye redness (1-2 years after diagnosis)
pretibial myxoedema- bilateral plaque formation on the anterior surface of lower legs, orange fell look, non pitting, 1-2 years after diagnosis
72
what causes exopthalamus
receptors in tissue and muscle surrounding the eye respond to TSI- causes water build up and retro-orbital swelling
collagen fibres may also be deposited which leads to loss of function and lack of movement
73
what is lid lag
delay of the upper eyelid on downward rotation of the eye
74
what hormone is predominantly secreted by thyroid adenoma and carcinomas
T3
75
what is de Quervains thyroiditis
acute inflammatory process usually due to viral that causes hyperthyroidisim along with fever, malaise, local tenderness of the thyroid
after a few will will transition into transient hypothyroidism the euthyroid
76
do you get goitres in iodine deficiency hypothyroidism
usually yes
77
what do antibodies attach in hashimotos
thyroid peroxidase (enzyme in production of thyroid hormones) and thyroglobulin
78
what are the secondary causes of hypothyroidism
deficiency or loss of function of the hypothalamus or pituitary: infiltration, infection or malignancy
79
what causes decreased TSH with normal T4 and T3
subclinical hyperthyroidism
80
what causes decreased TSH with decreased T4 and T3
pituitary disease
81
how are anti thyroid drugs dosed
start with high dose then reduce over 12-18 months
82
is agranulocytosis carbimazole or PTU
carbimazole
