Hypothyroidism

Question 1

Primary hypothyroidism definition

Answer 1

Underproduction of thyroid hormones T3 + T4, due to failure of thyroid gland.

Question 2

Causes of primary hypothyroidism

Answer 2

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.

Question 3

Epidemiology of primary hypothyroidism

• Location
• Incidence
• Sex
• Age

Answer 3

Location

• Western world= autoimmune
• Developing= iodine deficiency

Incidence

• 4:1000 a year
• Peak age= 30-50
• Sex= F>M, especially for Hashimoto’s

Question 4

Risk factors for primary hypothyroidism

Answer 4

• 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

Question 5

Thyroid hormone function and regulation

Answer 5

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.

Question 6

Subclinical hypothyroidism

Answer 6

Where TSH is elevated, but T3/4 levels are normal.
- Tends to have no obvious symptoms

Causes
- Partial thyroidectomy

Question 7

Pathology of Hashimoto’s disease

Answer 7

Autoimmune destruction of thyroid cells
- Diffuse lymphocytic infiltrates of cells

Elevated anti-thyroid peroxides
- Can also show elevated antithyroglobulin.

Question 8

Symptoms of hypothyroidism

Answer 8

Lethargy
Cold intolerance
Weight gain
Generalised weakness

Dry/coarse/ thinning hair
Puffy face
Constipation
Menorrhagia

Question 9

Signs of hypothyroidism

Answer 9

Slow reflexes

Bradycardia

Question 10

Investigations

Answer 10

Bloods

• TFT= elevated TSH >20
• Free T4 <9

Anti thyroid peroxidase antibodies
- Elevated.

Question 11

Management of primary hypothyroidism

Answer 11

Levothyroxine

• 100 mcg/ day
• Review after 6 weeks.
• Takes months for symptoms to regress.
• 25mcg/ day in elderly with ischaemic heart disease.

Question 12

Central hypothyroidism

Answer 12

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.

Question 13

Central hypothyroidism investigations

Answer 13

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.

Question 14

Hypothyroidism complications

Answer 14

Depression

Bradycardia

Hyperlipidaemia

Carpal tunnel syndrome

Heart failure

Coma