Hypothyroidism Flashcards
Primary hypothyroidism definition
Underproduction of thyroid hormones T3 + T4, due to failure of thyroid gland.
Causes of primary hypothyroidism
Most common
- Autoimmune thyroiditis (Hashimoto’s disease)
- Iodine deficiency (less common in western world)
Others
- Thyroidectomy
- Drugs: amiodarone, lithium.
- Radioactive iodine therapy (i.e. treatment for Graves’)
- Radiotherapy for head/ neck cancer.
RARE: sarcoidosis, haemochromatosis.
Epidemiology of primary hypothyroidism
- Location
- Incidence
- Sex
- Age
Location
- Western world= autoimmune
- Developing= iodine deficiency
Incidence
- 4:1000 a year
- Peak age= 30-50
- Sex= F>M, especially for Hashimoto’s
Risk factors for primary hypothyroidism
- Female
- Age 30-50.
- Iodine deficiency
- Drugs: amiodarone, lithium
- Family history
Autoimmune disorders: T1 DM, Vitiligo, Graves’ disease, Sjogren’s syndrome, Ovarian failure.
Radiology exposure
Thyroid hormone function and regulation
T4 produce in thyroid= converted to T3 in tissue.
T3 stimulates cellular oxygen consumption and energy generation.
- Regulate protein, fat and carb metabolism
- Metabolism of substrates vitamins and minerals.
Production of T4/3 is regulated by TSH, from anterior pituitary, via negative feedback.
Subclinical hypothyroidism
Where TSH is elevated, but T3/4 levels are normal.
- Tends to have no obvious symptoms
Causes
- Partial thyroidectomy
Pathology of Hashimoto’s disease
Autoimmune destruction of thyroid cells
- Diffuse lymphocytic infiltrates of cells
Elevated anti-thyroid peroxides
- Can also show elevated antithyroglobulin.
Symptoms of hypothyroidism
Lethargy
Cold intolerance
Weight gain
Generalised weakness
Dry/coarse/ thinning hair
Puffy face
Constipation
Menorrhagia
Signs of hypothyroidism
Slow reflexes
Bradycardia
Investigations
Bloods
- TFT= elevated TSH >20
- Free T4 <9
Anti thyroid peroxidase antibodies
- Elevated.
Management of primary hypothyroidism
Levothyroxine
- 100 mcg/ day
- Review after 6 weeks.
- Takes months for symptoms to regress.
- 25mcg/ day in elderly with ischaemic heart disease.
Central hypothyroidism
Low TSH (or TRH), low T3/4. - Due to dysfunction in pituitary/ hypothalamus
Causes
- Pituitary adenoma
- hypophysectomy/ radiation
- Head trauma
- Brain tumours around pituitary/ hypothalamus: meningioma, mets, cysts, craniopharyngioma.
- Infective: TB, syphlysis, toxoplasmosis.
Central hypothyroidism investigations
TFT
- Low or normal TSH
- Low free serum T4 (<9)
Rule out adenomas
- Prolactin= elevated in prolactinoma
- 9am serum cortisol= low in ACTH deficiency
- Serum testosterone/ gonadotrophins=Low
MRI brain, CT head
- Show lesions, especially pituitary adenoma.
Hypothyroidism complications
Depression
Bradycardia
Hyperlipidaemia
Carpal tunnel syndrome
Heart failure
Coma