Thyroid Flashcards
How does the thyroid feedback loop work?
1) Hypothalamus detects low blood level of T3/T4
2) Releases TRH to stimulate anterior pituitary
3) Anterior pituitary releases TSH to stimulate thyroid gland
4) Thyroid produces T3 & T4 (inactive)
What are the functions of T3?
↑Basal metabolic rate → ↑production of proteins ↑use of sugar + fats
↑Cardiac output
↑Bone resorption → thins bones
↑sympathetic nervous system
What is primary hypothyroidism?
Insufficient release of thyroid hormones from thyroid
↓T3/T4 and ↑TSH
What are the causes of primary hypothyroidism?
Iodine deficiency
Hashimoto
Drug induced: Amiodarone, Li, Contrast, Iodine
Riedel thyroiditis: Parenchyma replaced by fibrous tissue
Subacute de-Quervain’s thyroiditis: Post-virus
Congenital
What is Hashimoto’s?
Autoimmune destruction of thyroid T-cells
Causes hypertrophy & hyperplasia
Leads to more follicular damage
Eventual complete loss of function
What are the causes of secondary hypothyroidism?
Tumour of ant. pituitary
Damage to hypothalamus (trauma, tumour)
What is secondary hypothyroidism?
Insufficient production of TSH
↓TSH → ↓T3/4
What are the signs & symptoms of hypothyroidism?
↑weight/ oedema Fatigue, lethargy Constipation Menorrhagia Hoarse voice Cold ↓Memory + ↓Cognition Dry skin & coarse hair ↓HR (bradycardia) ↑BMI, ↓Reflexes Ataxia, Ascites, Effusion (lung & cardiac)
In which conditions would you have a non-painful & painful goitre?
Non-painful: Hashimoto & Riedel
Painful: De-Quervain’s
What are the signs of congenital hypothyroidism?
Excessive sleeping Mental retardation Intellectual disability Delayed physical growth Short height
How is hypothyroidism investigated?
TFTs: 1o: ↓T4 ↓T3; TSH high , 2o: ↓T4 ↓T3; TSH low/n
Thyroid Ab: Anti-TPO = Hashimoto’s
Lipids
How is hypothyroidism managed?
TSH <4 = TREATMENT
Levothyroxine: Adjust every 3-4w according to TSH
What are the SE of levothyroxine?
Hyperthyroidism
↓bone density (osteoporosis)
Worsening angina
AF
What are the complications of hypothyroidism?
Amiodarone SE
Myxoedema coma: Infection/surgery → ↓GCS + hypothermia, bradycardia, hypoglycaemia, unconscious
What is hyperthyroidism?
Excess release of T3/T4
What are the causes of hyperthyroidism?
Grave's Toxic multi nodular goitre Toxic adenoma Exogenous De Quervain's thyroiditis
What is Grave’s disease?
Circulating IgG auto-ABx
Bind to & activate G-protein thyrotropin receptors
Smooth muscle hyperplasia
↑T3 production
How does a toxic multi-nodular goitre cause hyperthyroidism? How is it Tx?
Autonomous secretion of T3/T4
Nuclear scintigraphy shows patchy uptake
Tx: Radioiodine
What are the signs & symptoms of hyperthyroidism?
↓weight Muscle wasting → Proximal myopathy Diarrhoea Oligomenorrhoea +/- infertility Sweating + heat intolerance Palpitations (AF) Tremor & hyperreflexia Thin hair Lid lag + lid retraction Palmar erythema
What are the signs of Grave’s disease?
1) Eye disease: Ophthalmoplegia
2) Pretibial myxoedema
3) Thyroid acropatchy: Clubbing, painful finger, toe swelling
Bruits
How is hyperthyroidism investigated?
TFTs: 1o = ↓or normal TSH ↑T4/T3 2o = ↑TSH ↑T4/T3
AutoAbx: TRAB (TSH receptor stimulating Abx), TPO
USS
Isotope scan: If antibodies negative (Cancer)
What is the management of hyperthyroidism?
1) B-blocker (Propanolol) for rapid Sx control
2) Carbimazole: Start high and titrate down
- Carbimazole + Thyroxine = Block & Replace
- Pregnant = propylthiouracil
3) Radioiodine 131i: Drink, often 1st line in teenagers
4) Thyroidectomy
What are the SE of carbimazole?
Agranulocytosis
Sepsis
Cholestatic jaundice
What are the complications of hyperthyroidism?
Thyrotoxic crisis/storm: Hyperthermia, mental disturbance, thyrotoxic Sx
Thyroid eye disease: Eye discomfort, diplopia, proptosis, afferent pupillary defect
