Thyroid gland Flashcards
what is the large cell surrounded by lots of small cells in a follicle
colloid
what is the small cells that surround the colloid cell in a follicle
follicular cells
what cells surround follicles
parafollicular C cells
what do follicular cells secrete
calcitonin
where are the follicular cells in between
what is their function
colloid cells
blood vessels
allow T3 and T4 into blood stream (from colloid cells)
is T3 or T4 secreted more
T4
what is T4
thyroxine
what is T3
tri-iodothyronine
what is T4 made from
2 DIT (di-iodo tyrosine) molecules
what is T3 made from
1 DIT (di-iodo tyrosine) and 1 MIT (mono-iodo tyrosine) molecule
% of T4 thats free
1%
what do the 99% of bound thyroxine (T4) bind to
thyroxine binding globulin (70%)
albumin
transthyretin (TTR)
why are most of T4 (thyroxine) bound in the blood
need to be bound to be transported
which type of T4 (thyroxine) is active (bound or free)
free
which type of thyroxine (T4) is measured when we measure T4 levels
free T4
what hormone does the hypothalamus produce in the hypothalamic pituitary thyroid axis
thyrotropin releasing hormone (TRH)
what hormone does the anterior pituitary release in response to thyrotropin releasing hormone (TRH)
thyroid stimulating hormone (TSH)
which cell does TSH (thyroid stimulating hormone) act on in the follicle
what does this cause
follicular cells
release of T4 and T3 from colloid cells
even though there is more T4 secreted, what happens to it when it reaches cells
turns in to T3
what converts T4 to T3
iodothyronine deiodinase (ID) types I, II and III
significance of IDI in T4 to T3 conversion
determines T3 in blood
significance of IDII in T4 to T3 conversion
what % of the overall T4 to T3 conversion is this
determines T3 in peripheral tissues
80%
significance of IDIII in T4 to T4 conversion
occurs in brain, fetal tissue, placenta
what are the 2 things taken up by the colloid cells for T3 and T4 synthesis
iodine thyroid peroxidase (TPO) enzyme
when are T3 and T4 released from colloid cells
what needs to happen to them before they are released
TSH stimulation
lysosomes break down thyroglobulin
what are the 2 types of thyroid receptors
beta and alpha
where are alpha thyroid receptors
peripheral tissues (basically everywhere = vast symptoms)
where are beta thyroid receptors
brain/thyroid feedback loop
generally what does the presence of thyroid hormones cause
increased metabolic rate
first line investigation for any ?thyroid problem
thyroid function tests - TSH, free T4, free T3
imaging options for ?thyroid problem (2)
ultrasound (with FNA if ?malignancy)
thyroid uptake scan (darker = more uptake = hyperthyroid (increased metabolism))
most common cause of hypothyroidism
hashimotos thyroiditis (chronic thyroiditis)
aetiology of hashimotos thyroiditis
autoimmune
which group of people (age and gender) are most likely to get hashimotos thyroiditis
middle aged females
same as all autoimmune conditions
autoimmune attack of thyroid peroxidase (TPO) = destruction of thyroid gland = reduced thyroid hormone production
hashimotos thyroiditis
goitre in hashimotos thyroiditis?
yes
bc its a chronic condition
which autoantibody is positive in hashimotos thyroiditis
anti-TPO
although hashimotos is a hypothyroid problem, what may happen in the initial stages of the disease
hyperthyroidism THEN hypothyroidism
apart from hashimotos thyroiditis what are the other aetiologies of primary hypothyroidism (6)
iodine deficiency
congenital
postpartum thyroiditis (in mums after birth , self limiting)
atrophic thyroiditis (acute thyroiditis)
drugs
post surgery
investigation results for primary hypothyroidism
low free T3/T4 high TSH (negative feedback)
where is the problem in primary hypothyroidism
thyroid gland itself
where is the problem in secondary hypothyroidism
above the thyroid gland (hypothalamus or pituitary)
in primary hypothyroidism bc TSH is high (negative feedback of low T3/T4), what else is high
prolactin
aetiology of secondary hypothyroidism (3)
vague things;
malignancy
drugs
infection (sick euthyroid syndrome)
why dont you check thyroid function tests in people with infection
sick euthyroid syndrome
completely normal, but T3/T4 are low - will fix itself so dont worry
overt hypothyroidism definition
clinical presentation
low T3/T4
subclinical hypothyroidism definition (investigation results)
high TSH, normal T3/T4 = probs dont have symptoms
BMI in hypothyroidism
high
face in hypothyroidism
‘toad like’
eyes in hypothyroidism (3)
exophthalmos
closed
puffy
heart in hypothyroidism
bradycardia (slow) - be careful of arrhythmias when treating if you treat it too fast
temp in hypothyroidism
cold
bowel movements in hypothyroidism
constipation
reflexes in hypothyroidism
slow
periods in hypothyroidism
menorrhagia - heavy periods (think hypo = slows things down = makes them worse = makes periods worse too)
hypothyroidism treatment
levothyroxine (T4)
levothyroxine dose in young for hypothyroidism
50-100ug
levothyroxine dose in old/CVD risk for hypothyroidism
25ug
medication advice for levothyroxine (when to take, what not to take with) for hypothyroidism
before breakfast
not at same time as Ca supplement, PPI, iron tablets
causes of levothyroxine malabsorption in hypothyroidism (2)
other drugs at same time - PPI, Ca supplement, iron tablets
coeliac disease
in pregnancy what do you do to levothyroxine dose in hypothyroidism
increase dose by 25ug
complication of untreated hypothyroidism
treatment
myxoedema coma - puffy face, hands
medical emergency - warm up, thyroxine slowly, ABCDE
aetiology of acute thyrotoxicosis (hyperthyroidism) (2)
thyroiditis - de quervains (viral infection), post partum, drug induced, hashimotos (before it turns hypothyroid)
thyroxine tablet overdose
aetiology of chronic thyrotoxicosis (hyperthyroidism) (3)
graves disease
thyroid nodules
thyroid cancer
for hyper and hypothyroid disease, when do goitres occur
if the condition is chronic (not acute)
aetiology of graves disease
autoimmune
most common cause of hyperthyroidism
graves disease
which group (age and gender) usually presents with graves
middle aged females
like all other autoimmune conditions
graves disease is an autoimmune condition, what thing is produced that causes the hyperthyroidism
what does it act like
what does this cause
thyroid stimulating immunoglobulin (TSI)
thyroid stimulating hormone (TSH)
increased T3 and T4 release
histology of graves disease
lymphoid follicles scattered through thyroid
presentation of graves disease (6)
hyperthyroid presentation (long list lol) symmetrical smooth goitre (sometimes) pretibial myxoedema thyroid bruit (on auscultation) graves eye disease clubbing of fingers (thyroid acropachy)
leg presentation of graves disease and description
pretibial myxoedema - bilateral plaques, red bumpy rash on legs
presentation of graves eye disease (4)
double vision (diplopia)
lid lag/lid retraction
protruding eyes
exophthalmos
treatment of severe graves eye disease
decompression surgery to bring down swelling
positive investigations in graves disease (4)
high T3/T4
low TSH (negative feedback)
anti-TPO positive (non specific, also positive in hashimotos)
TSH receptor antibody positive (TRAbs) - specific, not positive in hashimotos
thyroid uptake scan
treatment of graves (3)
carbimazole
surgery if severe
smoking cessation
investigation findings of primary hyperthyroid disease (2)
high free T3/T4 low TSH (from negative feedback)
investigation findings of secondary hyperthyroid disease (2)
high free T3/T4 high TSH (this is the cause)
investigation results for secondary hypothyroid disease (2)
low free T3/T4 low TSH (this is the cause)
in chronic hyperthyroid disease, what is the most likely aetiology for an elderly patient
thyroid nodules
asymmetrical rough goitre in hyperthyroidism
thyroid nodules
symmetrical smooth goitre in hyperthyroidism
graves disease
treatment of thyroid nodules causing hyperthyroidism
radioiodine
surgery
carbimazole long term
where is the problem in primary hyperthyroidism
thyroid gland itself
where is the problem in secondary hyperthyroidism
above the thyroid gland (hypothalamus or pituitary)
overt hyperthyroidism definition
has clinical evidence
high T4/T3
subclinical hyperthyroidism definition
low TSH but normal T4/3 = probs no symptoms
when do you treat subclinical hyperthyroidism
TSH <0.1
when do you treat subclinical hypothyroidism
TSH >10
BMI in hyperthyroidism
low
temp in hyperthyroidism
high
CNS response to hyperthyroidism (3)
tremor, anxiety, nervous
heart in hyperthyroidism (2)
tachycardia, palpitations
bowel habits in hyperthyroidism
diarrhoea
periods in hyperthyroidism
lighter
think hyper = speeds things up = makes them better
reflexes in hyperthyroidism
fast
skin in hyperthyroidism
thin skin
how does hyperthyroidism present in pregnancy
like hyperemesis - vomiting, nausea, tachycardia, warm
need to check TSH, will last >20 weeks (hyperemesis only lasts <20 weeks)
imaging for hyperthyroid disease (after TFTs)
thyroid isotope uptake scan to differentiate between graves, nodules etc
treatment physiology of hyperthyroid disease (antithyroid drugs)
block TPO (thyroid peroxidase enzyme ) = decrease T3 and T4 production
treatment options for hyperthyroid disease (4)
antithyroid drugs; carbimazole, propylthiouracil (PTU)
radioiodine
surgery
1st line treatment for hyperthyroidism
carbimazole
1st line treatment for hyperthyroidism in 1st trimester of pregnancy
propylthiouracil (PTU)
why is prophylthiouracil (PTU) preferred over carbimazole in 1st trimester of pregnancy
less potent
side effect of propylthiouracil (PTU)
why its not used all the time (just in 1st trimester of pregnancy
liver toxicity
side effect of all anti thyroid drugs (carbimazole, propylthiouracil (PTU))
agranulocytosis
NEED TO WARN PATIENTS need to stop drug immediately
patient with hyperthyroidism on carcbimazole develops mouth/throat infection
what do they have
what do you do
agranulocytosis (side effect of antithyroid drugs)
stop drug immediately, FBC looking for increased WCC (infection)
immediate symptomatic treatment for hyperthyroidism (bc the antithyroid drugs take a couple weeks to work)
beta blockers (propranolol)
2nd line treatment for graves after antithyroid drugs (carbimazole, propylthiouracil)
what do you give alongside this
radioiodine
need thyroxine replacement bc you destroy the entire thyroid gland (otherwise will cause hypothyroidism)
1st line treatment of nodules causing hyperthyroidism
radioiodine
treatment of hyperthyroidism if radioiodine contraindicated
what do you give alongside this
surgery
thyroxine bc you are destroying the thyroid gland = hypothyroidism
what do you need to watch out for in hyperthyroid patient with infection
management of this
sever hyperthyroidism (thyroid storm)
emergency treatment - ABCDE, ventilation, high dose steroids (inhibit conversion of T4 to T3), beta blockers, fluid etc etc
are solitary or multinodular thyroid goitres more common
solitary
types of benign thyroid nodule (3)
benign follicular adenoma
cyst
colloid nodule
are most thyroid nodules benign or malignant (%)
95% benign
most common malignant thyroid cancer (80%)
papillary thyroid cancer
what clinical condition can benign thyroid nodules cause
hyperthyroidism (thyrotoxicosis)
types of malignant thyroid cancer (5)
papillary thyroid carcinoma follicular thyroid carcinoma medullary thyroid carcinoma thyroid lymphoma anaplastic thyroid carcinoma
risk factors for thyroid cancer (3)
nuclear incidents/neck exposure
genetics (ask about family history)
iodine deficiency
which thyroid cancer is associated with hashimotos thyroiditis
papillary thyroid carcinoma
histology of papillary thyroid carcinoma (2)
'orphan annie' nucleus (looks like her big white eyes) psammoma bodies (collection of calcium)
are males or females more likely to get thyroid cancer
females
investigations for ?thyroid cancer
TFTs (thyroid function tests)
US (ultrasound) guided FNA (fine needle aspiration)
treatment of malignant thyroid cancer
surgery - lobectomy if AMES low risk, total thyroidectomy if AMES high risk
what does AMES stand for in determining the risk of thyroid cancer
Age
Metastasis
Extent of tumour
Size of tumour
eg high risk = >50, extrathyroidal if papillary OR capsular invasion if follicular, >5cm
after thyroid surgery for thyroid cancer, what do you need to give patient
levothyroxine
if prognosis generally good or bad for papillary and follicular thyroid cancer
good
5% mortality for papillary thyroid carcinoma
10% mortality for follicular thyroid carcinoma
how does papillary thyroid cancer spread
lymph nodes
how does follicular thyroid cancer spread
blood = bone, brain, lungs
what 2 groups of patients are associated with medullary thyroid carcinomas
40s/50s
young patients with MEN2 (familial phaeochromocytoma and medullary thyroid carcinoma)
where are medullary thyroid carcinomas
hence what do they secrete
parafollicular C cells
calcitonin
which thyroid cancer has worst prognosis bc it is v aggressive
anaplastic thyroid cancer
presentation of thyroid cancer
rough asymmetrical goitre
moves on swallowing
not painful
rough asymmetrical goitre with lymphadenopathy
papillary thyroid carcinoma
rough asymmetrical goitre with hoarseness
anaplastic thyroid carcinoma (v aggressive = vocal cord palsy)
aetiology of a multinodular goitre
pathophysiology
iodine deficiency
decrease in T3/T4 secretion = increase in TSH - increased thyroid gland size
what complication may a multinodular goitre have (bc its so big)
compression of trachea
when would you treat a multinodular goitre (you normally dont do anything)
if compression of trachea or ?cancer
viral infection
high T4/T3
low TSH
(few weeks later, more normal TFTs)
acute thyroiditis (cause by viral infection = dequervains thyroiditis)
aetiology of a goitre (5)
chronic hyperthyroidism chronic hypothyroidism benign thyroid cancer malignant thyroid cancer multinodular goitre (iodine deficiency)
how does congenital thyroid disease present in babies
poor appetite but normal weight (= weight gain)
delayed jaundice
aetiology of congenital thyroid disease (3)
missing thyroid
abnormally located thyroid
congenital pituitary disease
complication of baby with congenital thyroid disease that isnt treated within 3 months
cretinism (permanent developmental delay)
is acquired thyroid disease common in kids
no
