Hypothyroidism Flashcards
What will TFTs show in primary hypothyroidism?
TSH- high
T3/T4- low
What will TFTs show in secondary hypothyroidism?
TSH- low or normal
T3/T4- low
What is the definition of hypothyroidism?
Any disorder that results in insufficient secretion of thyroid hormones from the thyroid gland
What is myxoedema coma?
A hypothyroid emergency
In general, hypothyroidism is most common in which sex and of which age group?
Females, 65+
Hypothyroidism has a higher incidence in which race?
White populations
What environmental factor causes a higher incidence of hypothyroidism?
Areas of iodine deficiency
What are 5 causes of goitrous, primary hypothyroidism?
- Hashimoto’s thyroiditis
- Iodine deficiency
- Drug induced
- Maternally transmitted
- Hereditary defects
What 2 drugs have a big effect on thyroid function?
Amiodarone and lithium
How is hypothyroidism maternally transmitted?
If the mother is on anti-thyroid drugs
Is Hashimoto’s thyroiditis always goitrous?
No
What are 4 causes of non-goitrous, primary hypothyroidism?
- Hashimoto’s thyroiditis
- Post-ablative therapy
- Post-radiotherapy
- Congenital defects
What are 3 examples of self-limiting hypothyroidism?
- Following withdrawal of anti-thyroid drugs
- Subacute thyroiditis
- Post-partum thyroiditis
What causes secondary hypothyroidism?
Hypothalamic or pituitary disease
What are 6 causes of hypothalamic-pituitary disease?
- Infiltrative disease
- Malignancy
- Infection
- Cranial radiotherapy
- Congenital disorders
- Trauma
What effects can hypothyroidism have on the hair and skin?
- Vitiligo
- Coarse, sparse hair
- Periorbital puffiness
- Pale, cool, doughy skin
- Hypercarotenaemia
What effect does hypothyroidism have on thermogenesis?
Cold intolerance
What clinical sign appears in hypothyroidism as a result of abnormal fluid balance?
Pitting oedema
What effects can hypothyroidism have on the CV system?
- Decreased HR
- Cardiac dilatation
- Pericardial effusion
- Worsening of heart failure
What metabolic effects does hypothyroidism have?
- Hyperlipidaemia
- Weight gain and decreased appetite
What GI effects can hypothyroidism cause?
- Constipation
- Intestinal obstruction
- Ascites
What respiratory effects can hypothyroidism cause?
- Deep, hoarse voice
- Macroglossia
- Sleep apnoea
What neurological/CNS effects can hypothyroidism have?
- Depression, psychosis
- Muscle stiffness, cramps
- Peripheral neuropathy
- Decreased visual activity
What reproductive effects can hypothyroidism have?
- Menorrhagia
- Oligo/amenorrhoea (later)
- Hyperprolactinaemia
Hypothyroidism causes macrocytosis. What is this and what test will show it?
Enlarged red blood cells, increased MCV
What does hypothyroidism do to creatinine kinase?
Increases it
What does hypothyroidism do to LDL cholesterol?
Increases it
What effect does hypothyroidism have on sodium concentration and why?
Hyponatraemia- decreases renal tubular water loss
Why does hypothyroidism cause hyperprolactinaemia?
Increased TRH increased PRL secretion
What type of disease is Hashimoto’s thyroiditis?
Autoimmune
What are the two main antibodies involved in Hashimoto’s thyroiditis? Which is the major one?
Anti-thyroglobulin (60%) and anti-thyroperoxidase (95%)
Is TRAb ever present in Hashimoto’s thyroiditis?
Yes (10-20%)
Autoantibodies in Hashimoto’s thyroiditis cause antibody mediated, cell dependent cytotoxicity via what cell?
CD8+ T cells
How does cytokine mediated cell death occur in Hashimoto’s thyroiditis?
Gamma interferon from T cell activation recruits macrophages
What sex and age group is Hashimoto’s most common in?
Females, 45-60
What may precede Hashimoto’s thyroiditis?
Transient hyperfunction (hashitoxicosis)
What type of goitre will Hashimoto’s usually cause?
Diffuse, firm, painless
There is an increased risk of what type of cancer in the gland affected by Hashimoto’s thyroiditis?
B cell Non-Hodgkins Lymphoma
What other autoimmune conditions are most commonly affected with autoimmune thyroid disease?
Addison’s disease, pernicious anaemia, Type 1 diabetes
What is the main treatment of hypothyroidism?
Levothyroxine
What is the main risk of levothyroxine increasing metabolic rate?
Cardiac arrhythmias
What is the normal dosage of Levothyroxine?
50-100 macrograms daily
When should the normal dosage of levothyroxine be changed and what to?
In the elderly or those with ischaemic heart disease it should be 25-50 macro grams initially and adjusted every 4 weeks depending on response
Once TSH is stabilised with Levothyroxine, how often should levels be checked?
Every 12-18 months
Is there proven benefit of T3/4 combined treatment?
No
When in the day is levothyroxine preferably taken?
Before breakfast
What happens to the dose of levothyroxine in pregnancy and why?
It increases (usually by 25-50%) since pregnancy increases thyroid binding globulin
What drugs interfere with Levothyroxine?
Ca++ and iron tablets and PPIs
Who is most commonly affected by myxoedema coma?
Elderly females with longstanding but unrecognised or untreated hypothyroidism
Why is the mortality rate of myxoedema coma so high?
Co-morbidities
What 4 things may an ECG of someone with myxoedema coma show?
- Bradycardia
- Varying degrees of heart failure
- T wave inversion
- Prolonged QT interval
What type of respiratory failure will occur in myxoedema coma? What are the features of this?
Type 2- hypoxia, hypercapnia, respiratory acidosis
Co-existing failure of what is present in 10% of myxoedema coma patients?
Adrenals
How should patients with myxoedema coma be treated?
- ABCDE, intensive care
- Passively rewarmed
What is the major thing that should be monitored for in myxoedema coma?
Arrhythmias
What 4 things should be monitored in myxoedema come?
Oxygenation, urine output, fluid balance, blood sugars
What drugs should myxoedema coma patients be given?
Broad spectrum antibiotics and thyroxine (cautiously)
