Thyroid Gland Flashcards
what do follicular cells enclose
colloid
what does colloid contain
tyrosine containing thyroglobulin filled spheres
what do parafollicular C cells secrete
calcitonin
what is the main fuel for the thyroid gland
iodine
describe the synthesis and stoage of T3 and T4
iodine taken up by follicle cells
iodine attaches to tyrosine residues on thyroglobulin to form MIT and DIT
coupling of MIT + DIT = T3
coupling of DIT and DIT = T4
what is T4
thyroxine
accounts for 90%
converted to T3 by liver and kidney
what is T3
triiodothyronine
accounts for 10%
4x more potent
major biologically active hormone
properties of T3 and T4
hydrophobic and lipophilic so bind to plasma proteins
which plasma proteins do T3/T4 bind to
thyroxine binding globulin
thyroxine binding prealbumin
albumin
which form is biologically active - bound or unbound?
unbound
what is measured in hopsitals?
free T3/T4
states of increased TBG (increase total T4 but not fT4)
pregnancy, newborn OCP, tamoxifen, clofibrate, heroin Hep A biliary cirrhosis acute intermittent porphyria
states of decreased TBG (decrease total T4 but not fT4)
androgens cushings acromegaly systemic illness chronic liver disease nephrotic syndrome phenytoin, carbamzepine
metabolic effects of thyroid hormones
increase BMR and thermogenesis
increase blood glucose
mobilise fats from adipose tissue and increase fatty acid oxidation
increase protein synthesis
symptoms of hypothyroidism
slow pulse fatigue cold intolerance tendency to put on weight easily myxoedema cretinism in babies doughy skin periorbital puffiness coarse, sparse hair constipation hoarse voice carpal tunnel menorrhagia
symptoms of hyperthyroidism
fast pulse nervousness insomnia sweating heat intolerance tendency to lose weight easily palpitations tremor loose bowels eye symptoms brittle hair
most common thyroid cancer
papillary
worst prognosis thyroid cancer
anaplastic
types of differentiated thyroid cancer
papillary
follicular
features of differentiated tumours
take up iodine
secrete thyroglobulin
TSH driven
good prognosis
approximately how many present with mets in differentiated tumours
5%
spread of papillary
lymphatic
associations of papillary
Hashimoto’s thyroiditis
10yr mortality papillary
less than 5%
second most common thyroid cancer
follicular
spread of follicular
haematogenous
investigation of thyroid cancer
US guided FNA
excision for biopsy
gold standard treatment for thyroid cancer
surgery
- lobectomy
- subtotal or total thyroidectomy
AMES risk stratification
Age
Metastases
Extent of primary tumour
Size of primary tumour
what is it important to monitor post-operatively
calcium
what can be used as a tumour marker of recurrence in patients who have had surgery to remove a tumour
thyroglobulin
what is the most common cause of hypo or hyper thyroidism
autoimmune disease
hormone levels in hyperthyroid
low TSH
high fT3/4
hormone levels in hypothyroid
high TSH
low fT3/4
most common cause of goitrous hypothyroidism
Hashimoto’s thyroiditis
antibodies in Hashimoto’s
thyroid peroxidase (TPO) occasionally anti-thyroglobulin
what is seen on microscopy in Hashimotos
T cell infiltrate and inflammation
other primary causes of hypothyroidism
maternally transmitted iodine deficiency drug induced post-radiation/ablation subacute thyroiditis postpartum thyroiditis
causes of secondary hypothyroidism
hypothalamic - congenital, infection, infiltration, malignancy
pituitary - panhypopituitarism, TSH deficiency
management of hypo
thyroxine 50-100micrograms
in elderly with IHD, start at 25-50
when is TSH an index of therapeutic success?
primary hypothyroidism
of no use in secondary
what is myxoedema coma
severe hypothyroidism - typically affects old women with long standing hypothyroidism
signs of myxoedema coma
ECG - bradycardia, low voltage complexes, heart block, T wave inversion, QT prolongation
Type 2 resp failure
adrenal failure
treatment of myxoedema coma
ABCDE passively rewarm cardiac monitoring monitor vitals broad spectrum ABx
causes of hyperthyroid
Graves multi-nodular goitre toxic nodule subacute thyroiditis post partum amiodarone, thyroxine and lithium treatment kelp supplements
antibodies in Graves
TSH receptor antibodies
eye disease in graves
lid retraction lid lag chemosis proptosis visual loss diplopia exophthalmos
features of nodular thyroid disease
older patients with insidious onset
feels nodular
asymmetrical goitre
high uptake on scintigraphy
features of graves goitre
smooth symmetricl goitre
high scintigraphy uptake
see on US
what is thyroid storm
medical emergency
severe hyperthyroidism with resp and cardiac collapse
hyperthermia and exaggerated reflexes
Treatment of thyroid storm
Lugols iodine (potassium iodide) glucocorticoids PTU B Blockers fluids monitoring
medication for hyperthyroidism
carbimazole
PTU (preferred in pregnancy)
radio-iodine
side effects of carbimazole you do not want to miss
agranulocytosis
medication for symptomatic relief
beta blockers - propanolol
these are sympathomimetic
precautions with radio-iodine
no close contact for days after
no pregnancy for 6m after
high risk of hypothyroidism
risks of surgery
scar, general risks
recurrent laryngeal nerve palsy
hypothyroidism/hypoparathyroidism
what is DeQuervains thyroiditis
subacute viral
associated with sore throat/fever
usually self-limiting
subclinical thyroid disease results
mildly overactive - TSH low, T3/4 normal
mildly failing - TSH high and T3/4 normal
shin rash seen in Graves disease
pretibial myxoedema
HLA haplotypes for hypothyroidism
DR3/DR5
gene mutations in Hashimotos
CTLA-4 (negative regulator of T cell responses)
PTPN-22 (inhibitor of T cell function)
hashimotos associated with higher risk of what
B cell lymphoma
features of thyroid adenoma
discrete solitary mass
encapsulated by collagen cuff
nodule in papillary carcinoma
usually solitary, can be multifocal
often cystic and may be calcified (psammoma bodies)
features of anaplastic thyroid cancer
undifferentiated and aggressive
rapid growth
features of medullary thyroid cancer
associated with MEN 2
rare
derived from C cells (neuroendocrine) and so can secrete calcitonin
composed of spindle or polygonal cells arranged in nests, trabeculae or follicles
which type of cancer is associated with amyloid deposition
medullary
treatment of medullary
total thyroidectomy
Thy1
insufficient/uninterpretable
Thy2
benign
Thy3
atypia probably benign
Thy4
atypia suspicious of malignancy
Thy5
malignancy
