5. Hyperthyroidism Flashcards
what are the 2 causes of hyperthyroidism?
- Grave’s disease
2. nodular goitre (Plummer’s disease)
describe grave’s disease
an autoimmune disease where the whole gland is smoothly enlarged and the whole gland is overactive
how does grave’s disease trigger hyperthyroidism?
the immune system produces an antibody pretending to be TSH which binds to the TSH receptor and the thyroid gland becomes overactive
what are the 2 major symptoms of grave’s disease?
- exophthalmos
2. pretibial myxoedema
describe exophthalmos
thyroxine makes b-receptors more sensitive and makes your eyes wider than normal and other antibodies bind the muscles behind the eye, pushing the eye forward
describe pretibial myxoedema
antibodies stimulate the growth of soft tissue on the skin (hypertrophy)
how might a patient present with grave’s disease?
- exophthalmos
- localised myxoedema
- lid lag
- perspiration
- facial flush
- muscle wasting
- shortness of breath
- loss of weight
- rapid pulse
- warm, moist palms
- increased appetite
- tremor
- clubbing of fingers
- muscular weakness/fatigue
what is a scintigram?
a scan where radioactive iodine is given. the thyroid gland takes up iodine and can be visualised on the scan
describe plummer’s disease
toxic nodular goitre which is not autoimmune but the result of a benign adenoma that is overactive and produces too much thyroxine
what are the main differences you can see between grave’s disease and plummer’s disease?
in plummer’s disease there will only be a lump on one side not a smoothly enlarged thyroid
there are no autoimmune features (pretibial myxodeoma/exophthalmos) in plummer’s disease
the scintigram will show a hot nodule as opposed to the whole thyroid gland being enlarged
what are some clinical features of plummer’s disease due to the actions of throxine?
- increased BMR
- weight loss
- overheating
- increased sensitivity of the sympathetic NS
what are the effects of thyroxine on the sympathetic NS?
sensitises beta adrenoreceptors to low levels of adrenaline and NA so there is more sympathetic activation even when small amounts of adrenaline are released
what is thyroid storm?
hyperthyroidism when it becomes life threatening (medical emergency)
what are the features of thyroid storm?
- hyperpyrexia (temperature >41 degrees C)
- accelerated tachycardia (>170bpm)
- cardiac failure
- delirium/psychosis
- hepatocellular dysfunction, jaundice
2 or more symptoms are necessary for it to be a medical emergency
what are the aggressive treatment options for thyroid storm?
- surgery (thyroidectomy)
- radioiodine
- drugs
what drugs are used in the treatment of hyperthyroidism?
- thionamides (1st line treatment) e.g. propylthiouracil (PTU) and carbimazole (CBZ)
- potassium iodide
- radioiodine
- beta-blockers (to help symptoms)
why might drugs be given for reasons other than direct treatment?
- to prepare a patient for a thyroidectomy (lower heart rate)
- to reduce symptoms while waiting for radioactive iodine to act
what is the role of thyroid peroxidase in the production of thyroid hormones?
iodinates thyroglobulin and is involved in the coupling of mono/di-iodothyronines to make T3 or T4
how do thionamides work?
they inhibit thyroperoxidase enzyme, preventing the thyroid gland from making hormones
why do the clinical effects of thionamides take so long to show?
there is a store of thyroid hormones in the colloid so the biochemical effect takes hours and clinical effects are seen after several weeks
what is given to reduce side effects in the short-term?
propranolol (non-selective beta blocker) to reduce tremor and tachycardia
a cardio-selective beta blocker would only overcome palpitations, not the tremor
what are the other mechanisms of propylthiouracil (thionamide)?
- suppresses anti-TSH antibody production in Grave’s disease
- reduces the conversion of T4 to T3 in peripheral tissues
what are the unwanted actions of thionamides?
- agranulocytosis - fall in WBC count (usually reduction in neutrophils) however is rare and reversible
- rashes
describe the pharmacokinetics of thionamides
- drugs are in tablet form and are orally active
- carbimazole is a pro-drug so must be converted to methimazole first
- grave’s disease affects young people so women of reproductive age should be warned against pregnancy until dose is low because thionamides cross the placenta and are secreted in breast milk
- aim is to stop treatment after 18months
