Thyroid Tutorials Flashcards
what are thyroid follicles
balls of epithelial cells surrounding proteinaceous (non cellular) colloid
where are thyroid hormones stored
in colloid
how is T3 produced
de-iodination of T4 within target cells outside the thyroid
what do thyroid hormones bind to
serum proteins- thyroid binding globulin
what enzyme activates iodine
a peroxidase enzyme
how is tyrosine involved in thyroid hormones
tyrosine residues on thyroglobulin are iodinated forming MIT and DIT which couple together to form T4 and T3
what is thyroglobulin
protein made by thyroid cells
how are thyroid hormones secreted
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
what stimulated the thyroid to produce thyroid hormones
TSH secreted by the pituitary
what is thyrotropin
thyroid stimulating hormone
what are the types of goitre
diffuse and nodular
what are the 7 causes of goitres
iodine deficiency multinodular goitre graves disease thyroiditis tumour cysts inherited (abnormality of enzyme pathway or T4 receptor)
what can cause thyroiditis
(thyroiditis is an inflammatory response) hashimotos (autoimmune) subacute causes (de Quervains, viral) acute causes (bacterial) drugs (lithium, amiodarone)
what are the usual features of a malignant thryoid nodule
<20 and >70 years old male dysphagia/ dysphonia previous neck irradiation firm, hard, immobile cervical lymphadenopathy
what are usual features of a benign thyroid nodules
FHX of autoimmune diseases FHX benign nodules/ goitre associated hormone disturbances pain/ tenderness soft, smooth, mobile
how should thyroid lumps over 1.5 cm be investigated
ultrasound and fine needle aspirate (under ultrasound guidance)
what is a thyroid isotope scan useful for
establishing the cause of thyrotoxicosis- can identify multinodular goitres, toxic adenomas and thyroiditis
what antibodies can you check for in thyroid disease
anti TPO (thyroid peroxidase)
anti-thyroglobulin
TSH receptor antibody (TRAB)
what do thyroid function tests show in primary hypothyroidism
increased TSH
decreased T4/T3
what do thyroid function tests show in secondary hypothyroidism
decreased TSH
decreased T4/3
what do thyroid function tests show in hyperthyroidism
decreased TSH
increased T4/3
what do thyroid function tests show in subclinical hyperthryoidism
decreased TSH
normal T3/4
what do thyroid function tests show in sick euthyroid
normal or decreased TSH
decreased T4/3
what are the symptoms of hyperthyroidism
nervous, anxious, irritable warm, sweaty, heat intolerance tachycardia, palpitations, weight loss, increased appetite (10% have weight gain), diarrhoea, amenorrhoea, weakness, fatigue
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
what is a thyroid storm
CRISIS
untreated/ inadequately treated thyrotoxicosis + preciptating factors (MI, infection, PE)
rare but life threatening - medical emergency
what are the features of a thryoid storm
HR increased BP decreased fever altered mental status multiorgan failure
how do you manage a thyroid crisis
carbimazole (high dose) beta blockers hydrocortisone potassium iodide IV fluids +/- inotropes treat precipitating cause (MI, infection, PE)
what are the signs associated with graves
dysthyroid eye disease
thryoid acropathy
pretibial myxoedema
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)
describe thyroid acropachy
oft tissue swelling and periostial bone changes
what can worsen graves opthalmology
smoking and hypothyroidism
what are the clinical features of dysthyroid eye disease
grittiness, watery eyes, conjunctival injection, eyelid retraction, proptosis, visual blurring, painful eye movements
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
what are the secondary causes of hypothyroidism
pituitary or hypothalamic disease
what other than primary and secondary causes of hypothyoridism can cause hypothyroidism
peripheral resistance to thyroid hormone
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
what are the symptoms of hypothyroidism
fatigue lethargy cold intolerance weight gain dry puffy skin hair loss constipation menorrhagia muscle weakness bradycardia
what is the ultrasound classification for ultrasound thryoid cancers
U1-2 benign
U3- indeterminate
U4-5 malignant
what are 80% of all thyroid cancers
papillary cell carcinomas
what would been seen in thyroid tests for a goitre caused by menopause
suppressed TSH and raised T4
what is pemburtons sign
used to evaluate venous obstruction in patients with goiters. The sign is positive when bilateral arm elevation causes facial plethora
why do anti thyroid drugs take 3-4 weeks minimum to work
as stores of thyroid hormones
what should you be careful of when on antithyroid drugs
agranulocytosis- suppression of bone marrow, be aware of any sore throat or mouth ulcers
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
if a patient is non compliant to thyrotoxicosis meds what are their treatment options
radio iodine, sugery
what will probably happen eventually after radio iodine
will develop hypothyroidism, be on lifelong thyroxine
what antibodies for hypothryoidism
Anti-thyroid peroxidase (anti-TPO) antibodies or anti-thyroglobulin antibodies are found in 90-95% of patients with autoimmune thyroiditis
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)
what is the most common cause of hypopituitarism
a pituitary tumour
why does the thyroid move on swallowing
as it is attached to the upper end of the trachea
what cell types make up the thyroid
follicular cells (encase colloid) and parafollicular cells (lie within connective tissue)
what cell type produces thyroglobulin
follicular
what cell type produces calcitonin
parafollicular C cells
where is thyroglobulin stored
in the colloid
what is pinocytosis
occurs at colloid, causes the release of thyroglobulin
what acts on thyroglobulin to make thyroid hormones
lysosomes
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
where are T3 and T4 stored
in colloid thyroglobulin
what is the majority of secreted thyroid hormone
T4 (triiodothyronine)
where is T4 converted to T3
liver and kidneys
are T3 and T4 hydrophilic or phobic
phobic
calcitonin is phillic
what effects does thyroid hormone have on metabolism
increases protein synthesis, glucose and fatty acid plasma levels, thermogenesis, bone turnover and gut motility
what effect does growth hormone have on fat tissues
increases lipolysis, increasing plasma fatty acids
what effect does growth hormone have on the liver
increases gluconeogenesis, increasing plasma glucose
what effect does growth hormone have on muscle
increases protein synthesis, decreasing plasma amino acids
how does thyroid hormone affect fat storage
decreases it
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)
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
what hormone will always be raised in graves
T4 (T3 may be high or normal)
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
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
what is lid lag
delay of the upper eyelid on downward rotation of the eye
what hormone is predominantly secreted by thyroid adenoma and carcinomas
T3
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
do you get goitres in iodine deficiency hypothyroidism
usually yes
what do antibodies attach in hashimotos
thyroid peroxidase (enzyme in production of thyroid hormones) and thyroglobulin
what are the secondary causes of hypothyroidism
deficiency or loss of function of the hypothalamus or pituitary: infiltration, infection or malignancy
what causes decreased TSH with normal T4 and T3
subclinical hyperthyroidism
what causes decreased TSH with decreased T4 and T3
pituitary disease
how are anti thyroid drugs dosed
start with high dose then reduce over 12-18 months
is agranulocytosis carbimazole or PTU
carbimazole
