hyperthyroidism Flashcards
2 causes of hyperthyroidism
graves disease nodular goitre/plummers disease
features of graves (types of antibodies)
autoimmune as well- antibodies bind to TSH receptor in thyroid antibody 1 causes thyroid gland to grow and make thyroxine (goitre)= hyperthyroidism antibody 2 causes eyes to swell- binds to muscles behind eye= exopthalmos 3 causes swollen shins (pretibial myxoedema)- non-pitting when you press on it
features of graves eye disease
pushes eyes forward, keeping eyes open eyelids also kept open by adrenaline
feature of goitre and uptake test
smooth as whole gland enlarges- thats why in thyroid uptake test, radioactive iodine taken up by whole gland
features of plummers disease
not autoimmune, caused by benign tumour which is overactive, producing excessive T4 therefore no pretibial myxoedema or exophthalmos
neck in plummers disease and thyroid uptake test DIAGRAM
not smooth, a bulge forms on one side- the rest of the thyroid is fine and TSH is low, so it becomes smaller (although overall due to tumour patient still has hyperthyroidism) in radioactive uptake test, only the HOT TOXIC NODULE takes iodine, rest of gland doesn’t
effect of T4 on SNS
beta adrenoreceptors sensitised to normal levels of adrenaline/NA= tachycardia, tremor in hands, palpitations and lid lag (eye lid doesn’t come down with eyeball as adrenaline holds it back)
features of hyperthyroidism
weight loss with increased appetite SNS symtpoms sweating heat intolerance diarrhoea breathlessness
thyroid storm: danger and symptoms
excessive levels T4, with half of mortality untreated, so aggressive treatment needs hyperpyrexia (above 41 degrees), excessive tachycardia/arrhythmia, cardiac failure, confusion and jaundice- any 2 of these+ hyperthyroidism= admission into hospital
treatment of hyperthyroidism and their effect
thioamides (antithyroid drugs) potassium iodide radioiodine beta blockers first 3 reduce T4, last reduces symptoms
use of thioamines
daily treatment of hyperthyroidism (graves/toxic nodule) treatment before thyroidectomy (keeps thyroid function normal- also better to cause anaesthesia and patient less anxious) reduces symptoms whilst waiting for radioiodine to work
thyroid hormone synthesis DIAGRAM
uptake of iodide by active transport, then iodination of thyroglobulin using thyroperoxidase and H2O2 coupling reaction occurs then storage in colloid iodinated thyroglobulin then endocytosed using same enzyme and secreted as T4/3
mechanism of thionamides and problem, and solving problem
inhibits thyroid peroxidase= T3/4 synthesis and secretion store of thyroid hormone in colloid can still be used, thionamides simply stop production of new T3/4, hence clinical effect (reduction in symptoms) takes weeks thus, treatment involves beta blocker called propranolol to rapidly reduce tremor and tachycardia
other mechanisms of thioamides
reduces antibody production reduces conversion of T4 to T3 in peripheral tissues (PTU)
unwanted effects of thionamides
agranulocytosis- rare but can cause lower neutrophils (although reversible) rashes- common
pharmacokinetics of thionamides
orally active ie tablet carbimazole is prodrug which is converted to methimaole can cross placenta and is passed in breastmilk- so PTU preferred to carbimazole for pregnant women and breastfeeds its broken down in liver and excreted in urine
follow up from thionamides
after 18months, it is stopped, and patient reviewed periodically with thyroid function tests for relapse
role of beta blockers in thyrotoxicosis and when not given
it is non-selective which is good, stops many symptoms like tremors, heart rate etc not used for those with asthma, as blocks beta receptors in bronchial tree
potassium iodide- when is it used
only given when rapid reduction in symptoms is required for either preparing patients for surgery, or if they have a thyroid storm
mechanism of KI
dosage 30 times greater than daily requirement- causes autoregulatory effect called WOLFF-CHAIKOFF effect- prevents H202 and peroxidase, and inhibits iodination
effect of KI
symptoms reduced in a day, and size of glad/vascularity reduced after 10 days- better for surgery as smaller, and fact that symptoms are lower, so anaesthesia easier prior to surgery
unwanted action of KI
allergic reaction like rash, but rare
pharmacokinetics of KI
given orally (liquid/tablet)
radioiodine in high doses- mechanism and usefulness
emits beta particles in colloid to destroy follicular cells- thyroid gland permanently destoryed, so daily lifetime thyroxine needed
