Thyroid + Parathyroid Flashcards
what are the 5 main histological classifications of thyroid cancers?
papillary follicular medullary anaplastic other
which is the most common histological classification of thyroid cancer?
papillary
what histological appearance does differentiated thyroid cancer refer to?
papillary and folicular variants
do differentiated thyroid cancers tend to take up iodine?
yes
what do differentiated thyroid cancers tend to secrete?
thyroglobulin
what hormone drives differentiated thyroid cancers?
TSH
thyroid stimulating hormone
what risk factor has a strong association with thyroid cancer?
radiation exposure
do papillary thyroid cancers tend to spread via haematogenous spread or lymphatic spread?
lymphatic spread
what autoimmune condition is papillary thyroid cancer associated with?
Hashimoto’s thyroiditis
what is Hasimoto’s thyroiditis?
an autoimmune condition where the thyroid gland is attacked by a variety of cell and antibody mediated processes
what is the second most common histological type of thyroid cancer?
follicular
what thyroid cancer has a slightly higher incidence in regions relative to iodine deficiency?
follicular carcinoma
do follicular thyroid carcinomas tend to spread via haematogenous spread or lymphatic spread?
haematogenous spread
why is it uncommon to find lymph node enlargement in follicular thyroid carcinomas?
because lymphatic spread is rare
what are the 2 main ways of investigating a suspected thyroid cancer?
ultrasound guided fine needle aspiration
excisional biopsy of lymph node
what is the treatment of choice for a differentiated thyroid cancer?
surgery
what are the 3 main surgical options for thyroid cancer?
- thyroid lobectomy with isthmusectomy
- sub-total thyroidectomy
- total thyroidectomy
what are the 5 indications for total or subtotal thyroidectomy for a patient with thyroid cancer?
- DTC with extra thyroidal spread
- bilateral/multifocal DTC
- DTC with distant mets
- DTC with nodal involvement
- patient in AMES high risk group
when is whole body iodine scanning used post operatively?
in patients who have undergone subtotal or total thyroidectomy
how long post-op is whole body iodine scanning used after a subtotal or total thyroidectomy?
3-6 months
before a whole body iodine scan, when is T3 and T4 stopped?
T3 two weeks before
T4 four weeks before
if there is iodine uptake >0.1% in thyroid bed on whole body iodine scan post total/subtotal thyroidectomy, what is the management?
total remnant ablation
what are the 3 hormones the thyroid gland secretes?
thyroxine (T4)
tri-iodothyronine (T3)
calcitonin
what is a thyroid follicle made of?
follicular cells enclosing a colloid
what is the colloid filled with?
thyroglobulin
what are the cells within the thyroid gland that aren’t contained within the follicles?
parafollicular C cells
what hormone do parafollicular C cells contain?
calcitonin
what is the function of calcitonin?
minor role in calcium regulation
lowers serum calcium
compare the structure of T3 and T4?
T3 = MIT + DIT T4 = DIT + DIT
MIT = monoiodotyrosine unit DIT = di-iodotyrosine unit
where are T3 and T4 stored until required?
in colloid thyroglobulin
carbimazole and propylthiouracil are used in the treatment of hyperthyroidism, how do they work?
stop iodine attaching to the tyrosine units
therefore slow T3 and T4 production
which is secreted more- T3 or T4?
T4
which is more biologically active- T3 or T4?
T3
what is the main stimulus for T3 and T4 to be pulled in from colloid and to move across the follicular cell into the blood stream?
TSH from the pituitary gland
what are the 3 main carrier proteins for T3 and T4?
thyroxine binding globulin
thyroxine binding prealbumin
albumin
what do thyroid hormones do to basal metabolic rate?
increase basal metabolic rate
what do thyroid hormones do to thermogenesis?
increase thermogenesis
why do patients with hyperthyroidism present with shaking, sweating and palpitations?
increased responsiveness to adrenaline and noradrenaline (sympathetic ANS)
why is propanolol used in the treatment of hyperthyroidism?
to block exaggerated effect of sympathetic nervous system
what hormone, released from the hypothalamus, stimulates the release of TSH from the pituitary gland?
thyrotrophin releasing hormone
what hormones do T3 and T4 exert negative feedback control over?
Thyrotrophin Releasing Hormone (TRH)
Thyroid Stimulating Hormone (TSH)
what does stress do to the TRH and TSH release?
inhibits TRH and TSH release
when are the thyroid hormones at their highest and lowest?
thyroid hormones highest late at night
lowest in the morning
compare primary and secondary causes of hypothyroidism in terms of goitre (enlarged thyroid)?
primary gland failure- may have a goitre
secondary to TRH or TSH- no goitre
what is cretinism?
dwarfism and limited mental functioning due to deficiency of thyroid hormones present at birth
what is grave’s disease?
an autoimmune disease causing hyperthyroidism
what antibodies are present in grave’s disease and what is their function?
anti-TSH receptor antibodies:
- thyroid stimulating Ig
- thyroid growth stimulating Ig
- TSH binding inhibitor Ig
act in the same way as TSH but aren’t inhibited by T3 and T4
why can eyes bulge in hyperthyroidism?
exopthalmos
water retaining carbohydrate build up between the eyes
what is the anterior triangle of the neck bordered by?
superiorly- mandible
medially- midline
laterally- sternocleidomastoid
what is the posterior triangle of the neck bordered by?
inferiorly- clavicle
anteriorly- sternocleidomastoid
laterally- trapezius
when do thyroglossal cysts tend to present?
teenage years
what is a distinct feature of thyroglossal cysts?
moves with tongue
when do dermoid cysts tend to present?
teenage years
when do branchial cysts tend to present?
teenage years
when do cystic hygromas tend to present?
in 1sy year
compare primary hyperthyroidism to pituitary disease causing secondary hyperthyroidism in terms of levels of T3/4 and TSH?
primary: low TSH, high T3/4
secondary: high TSH, high T3/4
compare primary hypothyroidism to pituitary disease causing secondary hypothyroidism in terms of levels of T3/4 and TSH?
primary: high TSH, low T3/4
secondary: low TSH, low T3/4
what is myxoedema coma?
severe hypothyroidism
is pretibial myxoedema seen in hypo or hyperthyroidism?
hyperthyroidism
only Grav’es disease
what is pretibial myxoedema?
accumulation of hydrophilic mucopolysaccharides in the dermis
(usually seen in shins)
what are the 3 main classes of causes of primary hypothyroidism?
goitrous
non-goitrous
self-limiting
is chronic thyroditis (hashimoto’s thyroditis) a goitrous or non-goitrous cause of primary hypothyroidism?
goitrous
is atrophic thyroditis a goitrous or non-goitrous cause of primary hypothyroidism?
non-goitrous
is iodine deficiency a goitrous or non-goitrous cause of primary hypothyroidism?
goitrous
what is the most common cause of hypothyroidism in the western world?
Hashimoto’s thyroiditis
what is Hashimoto’s thyroiditis?
autoimmune destruction of the thyroid gland causing reduced production of thyroid hormones
what antibodies are present in Hashimoto’s thyroditis?
anti- thyroid peroxidase
anti-thyroglobulin
why does hypothyroidism cause hyperprolactinaemia?
decreased T3/4 causes increased TRH and TSH
increased TRH causes increased prolactin secretion
what dose of thyroxine should you start younger patients with hypothyroidism on?
50-100 micrograms
what dose of thyroxine should you start an older patient with history of ischaemic heart disease with newly diagnosed hypothyroidism on?
25-50 micrograms
once the dose of thyroxine has been estabilished, and hypothyroidism has been stabilised, how often should TSH levels be checked?
12- 18 months
why might exogenous thyroxine dose requirement increase during pregnancy?
because there is increased thyroxine-binding-globulin
compare primary and secondary hypothyroidism in the use of TSH levels as an indicator for if thyroxine treatment is working?
primary: TSH is a good indicator- will be low when T4 treatment is successful
secondary: TSH is not a good indicator, will be low regardless of if the treatment is successful
(in this case montor T4 levels)
what are the 5 findings of myxoedema coma on ECG?
- bradycardia
- low voltage complexes
- varying degrees of heart block
- inversion of T wave
- prolongation of QT interval
does myxoedema coma give type 1 or type 2 respiratory failure?
type 2 respiratory failure
what is the treatment of hyperthyroidism?
carbimazole
or
propylthiouracil
(+ symptomatic control with beta blockers for example)
in graves disease what is the treatment?
carbimazole/propylthiouracil
high dose then reduce over 12-18 months before stopping
(50% relapse risk)
what are the levels of T4 and TSH in sub-acute thyroditis?
T4- high in early stage, then low, then normal
TSH- low in early stage, then high, then normal
does amiodarone-induced thyrotoxicosis occur more frequently in areas with low or high iodine intake?
low iodine intake
does amiodarone-induced hypothyroidism occur more frequently in areas with low or high iodine intake?
high iodine intake
what are the levels of TSH and T3/4 in subclinical hyperthyroidism?
TSH- low
T3/4- normal
what are the levels of TSH and T3/4 in subclinical hypothyroidism?
TSH- high
T3/4- normal
what vertebra level does the thyroid tend to be at?
C5/6 -T1
embryologically, the thyroid descends from the foramen caecum to normal location along what duct?
thyroglossal duct
what embryological abnormality causes a lingual thyroid?
failure of thyroid descent
what embryological abnormality causes a retrosternal thyroid?
excessive descent
what embryological abnormality causes a thyroglossal duct cyst?
patent thyroglossal duct
where are TSH receptors found?
on the surface of thyroid epithelial cells
what happens to the intracellular levels of cAMP when TSH binds to the TSH receptors on teh surface of the cell?
increases cAMP levels
what does increasing intracellular concentration of cAMP levels within thyroid epithelial cells lead to? (in terms of hormone production)
increased T3/T4 production and release
what response elements within target genes, do T3/T4 bind to?
thyroid response elements
polymorphisms in what type of genes are associated with autoimmune thyroditis?
polymorphisms in immune regulation genes
what is thyrotoxicosis?
symptoms and signs that occur as a result of excess T3 and T4
what causes 85% of cases of hyperthyroidism?
grave’s disease
what age group does Grave’s tend to appear in?
20-40 year olds
what antibodies produced in grave’s disease may explain the episodes of hypofunction?
TSH binding inhibitor Ig
does iodine deficiency cause hyper or hypothyroidism?
hypothyroidism
what age group does Hashimoto’s thyroiditis tend to occur in?
40 - 60 years old
as well as autoantibodies, what cell type are important in the destruction of thyroid tissue in hashimoto’s?
cytotoxic T cells
as well as autoantibodies and cytotoxic T cells, what proteins are important in the destruction of thyroid tissue in hashimoto’s?
cytokines
esp gamma interferon
what may precede Hashimoto’s thyroiditis?
transient hyperfunction (Hashitoxicosis)
what form of malignancy is a recognised complication of Hashimoto’s thyroidits?
B cell NHL
a lymphomas
what is a goitre?
an enlargment of the thyroid gland
what are the 2 main types of goitre?
diffuse goitre
multinodular goitre
why does hypothyroidism cause goitre?
reduced T3/T4 production causes increased TSH levels which stimulates gland enlargment
what is the classic evolution of a goitre?
long standing diffuse goitre becomes a multi-nodular goitre
what cells are papillary and follicular thyroid carcinomas derived from?
thyroid follicular cells
do thyroid adenomas tend to be functional or non-functional?
non-functional
some adenomas are functional, what condition does this cause?
is this condition TSH dependent or independent?
thyrotoxicosis
TSH independent
what cells are medullary thyroid carcinomas derived from?
parafollicular C cells
how do you tell the difference between a follicular adenaoma and a follicular carcinoma in the thyroid gland?
follicular carcinoma needs vascular or capsular invasion
why can medullary thyroid carcinomas cause diarrhoea?
due to paraneoplastic syndrome: production of VIP
why can medullary thyroid carcinomas cause cushinds?
due to paraneoplastic syndrome: production of ACTH
describe the Thy 1 - Thy 5 thyroid cytology assessments?
Thy 1 - insufficient aspirate Thy 2 - benign Thy 3 - atypia, but probably benign Thy 4 - atypia, suspicious of malignancy Thy 5 -malignant
what cells are the parathyroid glands composed of?
chief cells supported by oxyphil cells
what hormone do chief cells within the parathyroid glands produce?
PTH
what is the function of PTH?
Calcium homeostasis
what is almost always the cause of hyperparathyroidism?
small adenomas
what are the 3 causes of hyperparathyroidism?
adenomas
hyperplasia
carcinoma
compare adenoma of parathyroid to hyperplasia of parathyroid in terms of glands affected?
adenoma: tends to be single gland
hyperplasia: tends to involve all glands
what causes secondary hyperparathyroidism?
chronic hypocalcaemia
what is the commonest cause of hypoparathyroidism?
post-op
what genetic condition can cause hypoparathyroidism?
Di George Syndrome
what happens to the binding of TBG in pregnancy?
binding increases
increases demand on thyroid
high levels of what hormone cause hyperemesis gravidarum?
high hCG
what does hCG do to the concentrations of TSH and T4?
high T4
causing neg feedback on TSH so low TSH
what is hyperemesis gravidarum?
severe sickness in pregnancy
as soon as pregnancy is suspected, what should you increase thyroxine dose by in a patient with hypothyroidism?
25 micrograms
what is gestational hCG-associated thyrotoxicosis?
when excess hCG (hyperemesis gravidarum) causes increased T4 leading to thyrotoxicosis
when should gestational hCG-associated thyrotoxicosis resolve by?
20 weeks
as levels of hCG increase what happens to the levels of thyroxine and the levels of TSH?
levels of thyroxine increase
levels of TSH decrease (due to T4 negative feedback)
why can transient neonatal thyrotoxicosis occur in a baby born to a mother with grave;s disease?
transient thyrotoxicosis due to graves antibodies crossing the placenta
in what trimester should you avoid the use of carbimazole?
1st trimester
what trimester is it safer to use propylthiouracil than carbimazole?
1st trimester
what is post partum thyroiditis?
transient hyperthyroxaemia 6 weeks after pregnancy which moves to hypothyroidism
what are the 4 main causes of superficial swellings in the neck?
- sebaceous cysts
- lipoma
- neurofibroma
- carbuncle
what are the 3 main causes of midlline swellings in the neck?
- thyroid swelling
- thyroglossal cyst
- dermoid cyst
what is the main infecting organism of a carbuncle?
staph
what are the 4 main causes of anterior triangle swellings in the neck?
- lymph nodes
- branchial cysts
- salivary glands
- carotid body tumour
what are the 2 main causes of posterior triangle swellings in the neck?
- lymph nodes
- cystic hygroma
what is the embryological origin of a carbuncle (superficial swelling of the neck)? [endoderm, mesoderm or ectoderm]
ectoderm
what is the embryological origin of a cystic hygroma (posterior triangle swelling of the neck)? [endoderm, mesoderm or ectoderm]
mesoderm
what is the embryological origin of a dermoid cyst (midline swelling of the neck)? [endoderm, mesoderm or ectoderm]
ectoderm
what is the embryological origin of a branchial cyst (anterior triangle swelling of the neck)? [endoderm, mesoderm or ectoderm]
mesoderm
what is the embryological origin of the thyroid (midline structure of the neck)? [endoderm, mesoderm or ectoderm]
endoderm
what is the embryological origin of a thyroglossal cyst (midline swelling of the neck)? [endoderm, mesoderm or ectoderm]
endoderm
what is the embryological origin of a neurofibroma (superficial swelling of the neck)? [endoderm, mesoderm or ectoderm]
ectoderm
when examining a neck lump what 6 features are you looking for?
- position
- size
- shape
- consistency
- mobility
- associated lymphadenopathy
what test is done to screen for congenital thyroid disease?
guthrie test
when is the guthrie test performed?
day 5
what hormone levels are measured by the guthrie screening test?
TSH
T4
does vit D increase or prevent loss of calcium from the kidney?
prevents loss
does vit D increase or prevent calcium uptake from the gut?
increases uptake
what type of receptor is the calcium sensor receptor?
g protein coupled receptor
what does calcium binding to the calcium sensor receptor do to the levels of PTH?
suppresses PTH
what is the function of PTH?
increases serum calcium by
- increasing gut absorption
- increasing resorption from bones
- increases reabsorption from the kidneys
what does vit D do to PTH?
suppresses PTH
if there is hypercalcaemia with suppressed PTH what does this indicate?
bone pathology
if there is hypercalcaemia with normal or high PTH what is the next test you should do?
urine calcium levels
if there is hypercalcaemia with normal or high PTH and high urine calcium, what does this indicate?
primary or tertiary hyperparathyroidism
if there is hypercalcaemia with normal or high PTH and low urine calcium, what does this indicate?
familial hypocalciuric hypercalcaemia
what are the 2 main causes of hypercalcaemia?
primary hyperparathyroidism
malignancy
what is primary hyperparathyroidism?
overactive parathyroid glands: PTH is produced irrespective of calcium levels
why does hyperparathyroidism cause osteopenia and increased risk of bone fractures?
high PTH causes high resorption of calcium from bones
what imaging can be used to detect which of the parathyroid glands is overactive?
sestamibi scan
what is secondary parathyroidism?
physiological high PTH in response to low calcium
what is tertiary hyperparathyroidism?
parathyroid becomes autonomously overactive after many years of secondary parathyroidism
which MEN type are parathyroid neoplasms associated with?
both 1 and 2
what type of inheritence is familial hypocalciuric hypercalcaemia?
autosomal dominant
what does familial hypocalciuric hypercalcaemia do to calcium sensing receptor?
makes it slightly insensitive
more calcium is needed for PTH suppression
what are the main 3 causes of hypocalcaemia?
hypoparathyroidism
vit D deficiency
chronic renal failure
compare intracellular and extracellular concentrations of calcium in a patient with hypomagnaseaemia?
intracellular Ca is high
extracellular Ca is low
what is pseudohypoparathyroidism?
a genetic defect causing PTH resistance
what are the levels of PTH in pseudohypoparathryoidism?
high
what is pseudo-pseudohypoparathyroidism?
a genetic defect causing PTH resistance
calcium is normal because PTH is high
compare calcium levels in a patient with pseudohypoparathyroidism and pseudo-pseudohypoparathyroidism?
pseudo- low calcium
pseudo-pseudo- normal calcium
