Thyroid disorders in practice Flashcards
What hormones does the thyroid gland produce?
T3 - tri-iodothyronine
T4 - thyroxine
2 drugs that can induce thyroid disorders
amiodarone
lithium
How does amiodarone cause hypothyroidism?
blocks the conversion of T4 to T3
causes an increase in TSH
How does amiodarone cause hyperthyroidism?
due to the iodine content of the drug
TFT monitoring before starting amiodarone
TSH
T3
T4
thyroid antibodies
TFT during treatment of amiodarone
TSH
T3
T4
Why do you do TFT after stopping amiodarone?
due to its long half life
Hypothyroidism occurs while taking amiodarone
add levothyroxine and continue amiodarone
How does lithium cause hypothyroidism?
inhibits iodine uptake and thyroid hormone release
TFT results for hypothyroidism?
high TSH
low T4
TFT results for hyperthyroidism
low TSH
high T4
TFT results for subclinical hypothyroidism
high TSH
normal T4
TFT results for subclinical hyperthyroidism
low TSH
normal T4
What is hypothyroidism?
impaired production of thyroid hormones
What is primary hypothyroidism?
failure of the thyroid gland to produce thyroid hormones
What is secondary hypothyroidism?
underproduction of TSH by the pituitary gland
subclinical hypothyroidism
usually asymptomatic
don’t need treatment unless symptoms (levothyroxine trial)
screening of TFTs
features of hypothyroidism
fatigue cold intolerance weight gain constipation myalgia (muscle pain) menstrual irregularities depression impaired concentration/memory dry skin/hair hair loss thyroid pain oedema vocal changes (hoarness) goitre bradycardia diastolic hypertension
complications of hypothyroidism
CV - dyslipidaemia, CHD, HF
reproductive - fertility, pregancy complications
neurological - deafness, concentration, memory
myxoedema coma - emergency
When to refer to endocrinologist with hypothyroidism?
goitre suspected Addison's disease pregnant/planning pregnancy cardiac disease atypical thryoid tests drug causes
1st line treaement for hypothyroidism
levothyroxine
dose of levothyroxine (under 65)
1.6 mcg/kg/day (nearest 25mcg)
increase 25-50 mcg every 3-4 weeks
maintenance dose of levothyroxine
100 - 200 mcg daily
levothyroxine dose over 60-65 years or IHD
25-50 mcg adjusted by 25mcg
How often TFTs when taking levothyroxine?
3 monthly until stabe TSH reached (2 similar measurements 3 months apart)
then annually
adverse effects of levothyroxine
GI disturbances CV - arrhythmais, tachycardia flushing, fever, heat intolerance weight loss hypersensitivity rxns - rash, oedema muscle cramps, weakness anxiety, tremour, restlessness, insomnia mania menstrual irregularities headache
levothyroxine drug interactions
calcium
antacids
iron salts
take at least 4 hours apart
timing of levothyroxine dose
30 mins before breakfast/caffeine/other drugs
What primarily causes primary hyperthyroidism?
Grave’s disease
How does Grave’s disease cause hyperthyroidism?
antibodies stimuate and increase secretion of thyroid hormones
causes of secondary hyperthyroidism
TSH secreting pituitary tumour
complications of hyperthyroidism
CV - AF, increased stroke risk
osteoporosis
eye disease - vision loss
thyroid storm - release of large amts of thyroid hormone, sudden worsening of symptoms, emergency, loss of consciousness
features of hyperthyroidism
breathlessness hyperactivity insomnia, irritability palpitations exercise intolerance heat intolerance fatigue muscle weakness incresed appetite, weight loss diarrhoea infertility, oligomenorrhoea, amenorrhoea polyuria itch reduced libido, gynaecomastia (men) hyperglycaemia (DM) sinus tachycardia, AF, HF eye signs goitre muscle wasting
management of hyperthyroidism
referral to specialist:
surgery
radioiodine treatment
antiithyroid drugs
When are antithyroid drugs used in hyperthyroidism?
- ST when waiting for specialist review
- ST prep for radioiodine treatment/surgery
- medium term when inducing remission of Grave’s
- LT radioiodine/surgery c/i/declines
What can be given to treat adrenergic symptoms of hyperthyroidism?
beta blocker - titrate dose until response
propranolol 10-40mg TDS/QDS
MR 80-160mg OD
asthma - diltiazem
How does radioiodine treatment work?
induces damage of DNA leading to death of thyroid cells
What measures should be taken after radioiodine treatment?
radioprotection - avoid close and prolonged contact with children/pregnant women for 3 weeks after
When is radioiodine treatment not recommended?
active thyroid eye disease (it can worsen it)
When is radioiodine treatment c/i?
pregnancy and breastfeeding
avoid pregnancy for 6 months after
men avoid having a child 4 months after
2 anti-thyroid drugs
carbimazole
propylthiouracil
How do anti-thyroid drugs work?
decrease thyroid hormone synthesis by acting as a preferred substrate for iodination by thyroid peroxidase the enzyme in thyroid hormone synthesis
What must be checked first before anti-thyroid hormone drugs?
FBC and LFT
Why is carbimazole preferred over propylthiouracil
propylthiouracil has a small risk of severe liver injury
When is propylthiouracil useful?
carbimazole not tolerated
pregnancy/trying to conceive
history of pancreatitis
When do Grave’s disease become euthyroid with carbimazole?
after 4 - 8 weeks
strategy for treatment with anti-thyroid drugs
high dose carbimazole given
repeat TFTs
if improving use either titration block regimen or block and replace regimen
titration block regimen (40%)
dose adjustment every 4-6 weeks
dose reduced if T4 falls too low/levels indicate hypothyroidism
block and replace regime (60%)
anti-thyroid drug used to block syhtnesis of thyroid hormone
T4 is monitored
levothyroxine is added
adjustments to levothyroxine dose made to maintain T4 levels in the reference range
adverse effects of carbimazole
nausea taste disturbances headache fever malaise arthralgia (joint stiffness) itch/rash bone marrow suppression - stop hepatobiliary disorders (jaundice) stop
What can be used to treat itch/rash caused by carbimazole?
antihistamines
dose of carbimazole
15 - 40mg daily
reduced to maintenance dose of 5 - 15mg
usually for 12 - 18 months
block and replace: 40 - 60mg daily
examples of bone marrow suppression caused by carbimazole
neutropenia and agranulocytosis
What are signs of bone marrow suppression caused by carbimazole?
signs of infection, sore throat and fever
What is preformed if there are signs of bone marrow suppression/infection and when? (carbimazole)
white blood cell count
on the same day
adverse effects of propylthiouracil
leucopenia cutaneous vasculitis aplastic anaemia nephritis hepatic disorders - hepatitis, hepatic failure, hepatic necrosis
propylthiouracil dose
200 - 400mg daily in divided doses
maintained until patient is euthyroid
dose gradually reduced to maintenance of 50 - 150mg daily in divided doses
Which is the more active thyroid hormone?
T3
T4 converted to T3 in peripheral tissues
