Hypothyroidism Flashcards
What are the 3 types of hypothyroidism?
Goitrous
Non-goitrous
Self-limiting
What are some causes of goitrous hypothyroidism?
- Hashimoto’s thyroiditis (Chronic thyroiditis)
- Iodine deficiency
- Drugs (e.g. amiodarone, lithium)
- Maternally transmitted (e.g. anti-thyroid drugs)
- Hereditary biosynthetic defects
What are some causes of non-goitrous hypothyroidism?
- Atrophic thyroiditis
- Ablative surgery (e.g. radioiodine, surgery)
- Radiotherapy
- Congenital developmental defect
What are some causes of self-limiting hypothyroidism?
- post-partum thyroiditis
- withdrawal of antithyroid drugs
- subacute thyroiditis
What is Hashimoto’s thyroiditis?
Hashimoto’s thyroiditis is an autoimmune condition causing chronic thyroiditis and therefore hypothyroidism
It results in autoimmune destruction of the thyroid gland, leading to reduced thyroid hormone production
What is the most common cause of hypothyroidism in the Western world?
Hashimoto’s thyroiditis
Who is most at risk of Hashimoto’s thyroiditis?
Younger patients
Females
Family history
What immune components are present in Hashimoto’s thyroiditis?
- CD8+ T cells
- Anti-thyroid antibodies
- Gamma-interferon + Macrophages
- Lymphocytes
What antibodies are found in Hashimoto’s thyroiditis?
- Anti-TPO (Thyroid PeriOxidase)
- Anti-thyroglobulin
What will histological testing show in Hashimoto’s thyroiditis?
Prominent lymphoid infiltrate, containing:
- Lymphocytes
- Plasma cells
- Reactive follicles with germinal centres
There will also be thyroid follicle atrophy, causing the formation of Hurthle cells (Follicular cells that incorrectly regenerate, leading to eosinophilic cytoplasm formation)
May see progressive fibrosis within the glan
What are Hurthle cells?
Follicular cells that incorrectly regenerate, leading to eosinophilic cytoplasm formation)
What are some causes of secondary hypothyroidism?
- Infection
- Malignancy
- Trauma
- Congenital
- Cranial radiotherapy
- Drugs
What are the main symptoms and signs of hypothyroidism?
- Reduced basal metabolic rate
- Slow pulse rate
- Fatigue, lethargy, slow response times and mental sluggishness
- Cold-intolerance
- Tendency to put on weight easily
What is caused by reduced BMR in hypothyroidism?
Reduced basal metabolic weight means there may be hyperlipidaemia and decreased appetite (But still weight gain)
What are some hair and skin symptoms of hypothyroidism?
- Coarse, sparse hair
- Dull, expressionless face
- Periorbital puffiness
- Pale cool skin that feels doughy
- Vitiligo
- Hypercarotenaemia (yellow skin-pigmentation)
What is vitiligo?
Vitiligo is a skin condition that forms as a result of a number of autoimmune conditions
What are some cardiac symptoms of hypothyroidism?
- Cardiac dilatation
- Pericardial effusion
- Worsening of heart failure
- Pitting oedema
What are some gastrointestinal symptoms of hypothyroidism?
- Constipation
- Megacolon
- Intestinal obstruction
- Ascites
What are some respiratory symptoms of hypothyroidism?
- Deep hoarse voice
- Macroglossia
- Obstructive sleep apnoea
What are some neurological symptoms of hypothyroidism?
- Decreased intellectual and motor activity
- Depression and psychosis
- Muscle stiffness and cramps
- Peripheral neuropathy
- Prolongation of tendon jerks
- Carpal tunnel syndrome
- Decreased visual acuity
What are some gynaecological symptoms of hypothyroidism?
- Menorrhagia
- Oligo or amenorrhoea
- Hyperprolactinaemia
What are the main 2 tests performed in hypothyroidism?
Free T3/4
TSH
How will primary hypothyroidism be shown on blood testing?
Low fT3/4
High TSH
How will secondary hypothyroidism be shown on blood testing?
Low fT3/4
Low TSH
What other blood test results are suggestive of hyperthyroidism?
- Raised MCV
- Raised Creatinine kinase
- Raised LDL
- Hyponatraemia
- Hyperprolactinaemia
- Possibly anti-TPO, anti-thyroglobulin and TSH-receptor antibodies (TRAb)
What is the most common antibody found in autoimmune (e.g Hashimoto’s thyroiditis) hypothyroidism?
Anti TPO (95%)
What is the leats common antibody found in autoimmune hypothyroidism?
TRAb (10-20%)
Why should basal metabolic rate be increased gradually in hypothyroidism?
Rapid restoration may precipitate cardiac arrhythmia
How is hypothyroidism managed in younger patients?
- Start levothyroxine (50-100ug daily)
- Check TSH 2 months after any dose change
- Check TSH every 12-18 months once stabilised
How is hypothyroidism managed in elderly patients?
- Start levothyroxine (25-50ug daily, adjusted every 4 weeks)
- Check TSH every 4 weeks and adjust if necessary
- Check TSH 2 months after any dose change
- Check TSH every 12-18 months once stabilised
How should secondary hypothyroidism be managed?
In secondary hypothyroidism, titrate dose of levothyroxine to the fT4 level
What is levothyroxine?
Levothyroxine is a T4 hormone analogue, preferably taken before breakfast
Why is T3 therapy rarely used?
It is immediately biologically active, so levels in the blood do not last long
What is a myxoedema coma?
A coma caused by extreme hypothyroidism
Who is most at risk of myxoedema coma?
Elderly women with long standing but frequently unrecognised or untreated hypothyroidism
What is the mortality rate of myxoedema coma?
Around 60% despite early diagnosis and treatment
What investigations are required in myxoedema coma?
ECG
ABG
What will be shown on ECG in myxoedema coma?
- Bradycardia
- Varying degrees of heart block
- T wave inversion
- Prolongation of QT interval
What will be shown on ABG in myxoedema coma?
- Hypoxia
- Hypercarbia
- Respiratory acidosis
How is myxoedema coma managed in ICU?
- Passive rewarming
- Cardiac and urine output monitoring
- Broad spectrum antibiotics
- Thyroxine cautiously (Hydrocortisone)
Why is levothyroxine dose increased in pregnancy?
During pregnancy, strain on the thyroid increases, meaning that in pre-existing hypothyroidism, the thyroid is unable to compensate for increased demand in pregnancy, even when treated with levothyroxine
By how much is levothyroxine dose increased by in pregnancy?
25mg as soon as pregnancy is suspected
How often are thyroid function tests performed in pregnancy?
Monthly thyroid function tests are performed then for the first 20 weeks, then every 2 months until term
What is the average dose increase in levothyroxine by week 20?
50% increase
What is the TSH level aimed for in pregnancy?
<3-4 mU
What are some complications of untreated hypothyroidism in pregnancy?
- Increased abortion
- Pre-eclampsia
- Abruption
- Post-partum
- Haemorrhage
- Preterm labour
- Foetal neuropsychological underdevelopment (7 IQ point average decrease)
