Hypothyroidism Flashcards

1
Q

Primary hypothyroidism definition

A

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

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2
Q

Causes of primary hypothyroidism

A

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.

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3
Q

Epidemiology of primary hypothyroidism

  • Location
  • Incidence
  • Sex
  • Age
A

Location

  • Western world= autoimmune
  • Developing= iodine deficiency

Incidence

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

Risk factors for primary hypothyroidism

A
  • 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

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5
Q

Thyroid hormone function and regulation

A

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.

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6
Q

Subclinical hypothyroidism

A

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

Causes
- Partial thyroidectomy

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7
Q

Pathology of Hashimoto’s disease

A

Autoimmune destruction of thyroid cells
- Diffuse lymphocytic infiltrates of cells

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

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8
Q

Symptoms of hypothyroidism

A

Lethargy
Cold intolerance
Weight gain
Generalised weakness

Dry/coarse/ thinning hair
Puffy face
Constipation
Menorrhagia

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9
Q

Signs of hypothyroidism

A

Slow reflexes

Bradycardia

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10
Q

Investigations

A

Bloods

  • TFT= elevated TSH >20
  • Free T4 <9

Anti thyroid peroxidase antibodies
- Elevated.

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11
Q

Management of primary hypothyroidism

A

Levothyroxine

  • 100 mcg/ day
  • Review after 6 weeks.
  • Takes months for symptoms to regress.
  • 25mcg/ day in elderly with ischaemic heart disease.
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12
Q

Central hypothyroidism

A
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.
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13
Q

Central hypothyroidism investigations

A

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.

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14
Q

Hypothyroidism complications

A

Depression

Bradycardia

Hyperlipidaemia

Carpal tunnel syndrome

Heart failure

Coma

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