7. Thyroid disease Flashcards
How do TSH and free T4/T3 levels relate to thyroid activity?
Hypothyroidism
- increseased TSH
- decreased free T4/T3
Hyperthyroidism
- decreased TSH
- increased free T4/T3
What is a goitre and what are the 3 types?
Swelling of the thyroid gland:
- diffuse
- multinodular
- single nodule
What is the prevalence of goitre in UK?
1% males
7% females - oestrogen/progesterone ratio affects thyroid function
At which stages in life can physiological goitre (normal thyroid function) occur at?
- menarche
- pregnancy
- menopause
What is the most common cause of goitre globally?
Iodine deficiency: reduced thyroxine levels… increased TSH… generalised thyroid enlargement (usually nodular).
Severe cases can become hypothyroid.
What is the most common cause of goitre in the UK?
Multinodular goitre
- affects 5% of Western pops.
- 7x more common in women
- aetiology unknown
What is the thyroid function in multinodular goitre?
normal, though very small no. may develop hyperthyroidism after many years (toxic multinodular goitre).
Why is iodine deficiency a particular concern during pregnancy?
If mother is iodine deficient and hypothyroid then the foetus is also iodine deficient. Leads to cretinism: - mental retardation - abnormal gait - deaf-mutism - short stature - goitre - hypothyroidism
Name a possible complication of multinodular goitres.
may enlarge inferiorly into superior mediastinum to form a retrosternal goitre - may cause tracheal compression and respiratory problems (inspiration stridor)
Name a 3rd possible cause for goitre (without metabolic dysfunction). How does this present and what is the prognosis?
thyroid cancer (<1% of all cancers in UK)
- don’t cause metabolic disturbance
- present as thyroid nodule
- prognosis is excellent - 97% cure rate
Name some hypothyroidism symptoms.
1- lethargy
2- weight gain
3- intolerance to cold
4- bradychardia
5- constipation
6- dry skin
7- hair loss (alopecia), esp. outer 1/3 of eyebrows
8- myoedema (puffy eyes, face, hands and feet) and associated carpal tunnel syndrome symptoms
9- hoarse voice
10- memory problems, depression, psychosis (myxoedema medness)
11- menorrhagia
Name some signs of hypothyroidism.
- weight gain
- dry skin, coarse brittle hair, loss of outer 1/3 of eyebrows
- pallor - ‘peaches and cream’ face
- coarse facial features and periorbital puffiness
- bradycardia
- hyporeflexia with delayed relaxation
- non-pitting oedema - myxoedema - around eyes, hands and feet
- ascites or pericardial effusion (both uncommon)
Why does myxoedema occur in hypothyroidism?
deposition of mucopolysaccharides
What is the main cause of hypothyroidism?
Hashimoto’s disease (autoimmune destruction of thyroid follicles) - antibodies to thyroglobulin and thyroid peroxidase are present in blood
10x more frequent in women
Is Hashimoto’s disease associated with goitre?
may be associated in early stages with a small diffuse goitre (due to inflammation)
Apart from autoimmunity, name possible causes for hypothyroidism.
- severe iodine deficiency
- post-surgical removal of thyroid with inadequate thyroxine replacement
- TRH or TSH deficiency
What is the treatment for hypothyroidism?
Oral thyroxine (longer 1/2 life) - adjust dose to normalise serum TSH
What is the difference between hyperthyroidism and thyrotoxicosis?
Hyperthyroidism = thyrotoxicosis due to over production of thyroxine by thyroid gland
What are the symptoms of thyrotoxicosis?
- weight loss in spite of increased appetite and increased bowel movement/diarrhoea
- irritability, anxiety, insomnia
- heat intolerance, sweating warm vasodilated hands
- tachycardia and palpitations
- fatigue, weakness esp. of proximal muscles (buttocks and thighs)
- amenorrhea
Name some signs of thyrotoxicosis.
- weight loss
- warm sweaty hands
- fine hand tremor
- tachycardia, atrial fibrillation
- bounding pulse - wide pulse pressure
- proximal myopathy
- lid lag and staring eyes
Why are lid lag and staring eyes signs of thyrotoxicosis?
Lids controlled by levator palpebrae superioris muscle (90% skeletal muscle and 10% smooth muscle) - SM portion supplied by sympathetic nervous system.
Overstimulation of sympathetic portion causes signs.
Suggests possible causes for hyperthyroidism. Which is the most common?
- Graves’ disease (most common)
- Toxic multinodular goitre
- Toxic adenoma (benign tumour causing overactivation)
- Ectopic thyroid tissue
What is Graves’ disease?
Autoimmune disease resulting in hyperthyroidism. Caused by production of thyroid stimulating immunoglobulin (TSI) which continually stimulates TSH receptor and thyroid hormone secretion outside normal negative feedback control.
Which features are unique to Graves’ disease in addition to the symptoms of thyrotoxicosis?
- exopthalmos - bulging of eyes anteriorly out of orbit
2. pre-tibial myxoedema (5% of Ps)
What are the treatment options for thyrotoxicosis?
- carbimazole
- pro-drug converted to methimazole in body
- prevents thyroid peroxidase from coupling and iodinating the tyrosine residues on thyroglobulin, thereby reducing T4 production - thyroidectomy - surgical excision of thyroid
- ablative dose of radioactive iodine
Which drug can affect thyroid function? Explain why.
Anti-arrhythmic drug AMIODARONE - similar structure to thyroxine so can affect thyroid function (can cause hypo- or hyperthyroidism)
