Hypothyroidism Flashcards
Where does primary hypothyroidism arise from?
Thyroid gland itself
What are the three classifications of primary hypothyroidism?
Goiterous
Non-goiterous
Self limiting
What can cause a goiterous primary hypothyroidism?
Hashimoto’s thyroiditis
Iodine deficiency
Maternally transmitted anti thyroid agent
Drug induced
What is Hashitmoto’s thyroiditis?
Autoimmune disease
destruction of thyroid gland
chronic inflammation
What is the etiology of Hashimoto’s?
F>M
FHx AID
What auto antibodies are involved in Hashimoto’s?
Anti TPA (thyroid peroxidase antibodies)
What can be seen on miscroscopy of Hashimoto’s?
T cells and inflammation
What drugs can cause a goiterous primary hypothyroidism?
Amiodarone
Lithium
IL-2
IFN alpha
What are the causes of a non goiterous primary hypothyroidism?
Post radiation
Atrophic thyroiditis
Post ablative/surgey
Congenital
What are the self limiting causes of primary hypothyroidism?
Withdrawal of thyroid suppressive therapy
Post partum thyroiditis
Subacute/chronic with transient hypothyroid
Where are the sites of secondary hypothyroidism?
Hypothalamus
Pituitary
What hypothalamic causes of secondary hypothyroidism are there?
infection eg encephalitis
infiltration eg sarcoidosis
neoplasm eg craniopharyngioma
congenital
What pituitary causes of secondary hypothyroidism are there?
panhypopituitarism TSH deficiency infection infiltration neoplasm trauma
What laboratory tests can be used to show hypothyroidism?
Raised TSH Low fT4 Low fT3 Raised CK Raised LDL Reduced Na+ (less renal tubule water loss)
What test needs to be done to rule out B12 deficiency?
Test for macrolytes
What are the hormone levels in
a) primary overt hypothyroidism?
b) primary subclinical hypothyroidism?
c) secondary hypothyroidism?
a) Raised TSH, Low fT4, Low fT3
b) Raised TSH, normal fT4, normal fT3
c) Low/normal TSH, low fT4, normal/low fT3
What are the hair and skin changes in hypothyroidism?
Dry skin Periorbital puffiness Pale, cold, doughy skin Coarse, sparse hair Pitting oedema (fluid retention)
What are the thermogenesis changes in hypothyroidism?
Cold intolerance
What are the cardiac changes in hypothyroidism?
Bradycardia
Cardiac dilatation
worsening heart failure
pericardial effusion
What are the gynaecological changes in hypothyroidism?
Menorraghia (heavy periods)
may lead to oligio or amenorrhoea
What are the changes to the metabolic rate in hypothyroidism?
Increased appetite
Weight gain
hyperlipidaemia
What are the GI changes in hypothyroidism?
constipation
megacolon
obsruction
ascites
What are the repiratory changes in hypothyroidism?
deep hoarse voice
obstructive sleep apnoea
What antibodies are found in autoimmune hypothyroidism?
Anti TPO (90%) Anti TSH receptor (10-20%) blocking effect Anti Thyroglobulin (60%)
How can you treat hypothyroidism?
Thyroxine
50-100 ug in young
25-50 ug in elderly
Take before breakfast (food often changes pH)
How does treatment for hypothyroidism need monitored?
adjust every 4 weeks according to response
check TSH levels every 2 months after a dose change
once stable check TSH every 12 months
How does rapid restoration of metabolic rate affect patient?
May percipatate arrythmias
What changes to thyroxine dose need to be considered in pregnancy?
May need to increase dose
What is myxoedema in the context of hypothyroidism?
Very severe hypothyroidism
Can lead to myxoedema coma
What are the signs of myxoedema in a) adult
b) baby/child
a) puffy face, hands, feet
b) cretinism: dwarf, limited mental functioning
What is the etiology of a myxoedema coma?
Elderly women
undiagnosed/untreated hypothyroidism
What are the ECG findings in a myxoedema coma?
Bradycardia
pronlonged QT
Low voltage complexes
Maybe heart block
What are the respiratory effects in a myxoedema coma?
Thype 2 repiratory failure
hypercabia
hypoxia
respiratory acidosis
What happens to the adrenals in myxoedema coma?
co existing failure of adrenals
What is the treatment for a myxoedema coma?
intensive care ABCDE passively rewarm monitor: ECG, BP, urine output, Sp02 Fluids, electrolytes Broad spectrum antibiotics
Why does special care have to be taken when perscribing amiodarone?
causes thyrotoxicosis in low iodine areas
hypothyroidism in iodine overdose
How is management of hyothyroidism changed in pregancy?
increase thyroxine my 25mcg as soon as pregnancy suspected
check TFTs monthly for 20weeks then 2 monthly until term
average dose increase is by 50%
aim for TSH
What are the risks of untreated hypothyroidism in pregnancy?
abortion preeclampsia abruption postpartum hge preterm labour
How does gestational hCG associated thyrotoxicosis happen?
hyperemesis gravidarum(high hCG, low TSH)
resolves in 20wks
(only treat if persists past this)
