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4th Year Endocrinology > Hyperthyroidism > Flashcards

Hyperthyroidism Flashcards

1
Q

Definition of hyperthyroidism

A

Hyperthyroidism reflects an increased level of circulating thyroid hormone leading to raised metabolic rate and sympathetic nervous system activation.

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2
Q

Thyroid function physiology

A
  • Hypothalamus produces thyroid-releasing hormone (TRH)
  • Which stimulates the anterior pitiuitary to release thyroid-stimulating hormone (TSH)
  • Which acts on the thyroid which produces T4 and some T3
  • T4 is activated (converted to T3) by peripheral tissue: liver, kidney, brain and skeletal muscle
  • Negative feedback to hypothalamus
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3
Q

Pathophysiology of primary hyperthyroidism

A
  • Excessive production of T3/T4 by the thyroid gland
  • Thyroid gland pathology
  • Most common subtype
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4
Q

Pathophysiology of secondary hyperthyroidism

A
  • Stimulation of the thyroid gland by excessive TSH
  • Originates due to pathology of the pituitary or hypothalamus
  • May also be secondary to a TSH-secreting tumour
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5
Q

Common causes of primary hyperthyroidism

A
  • Graves’ disease
  • Toxic multinodular goitre
  • ​Toxic adenoma (single autonomous functional nodule)
  • Thyroiditis
    • Transient hyperthyroidism occurring before hypothyroidism due to Hashimoto’s and De Quervain’s thyroiditis
  • Subclinical hyperthyroidism
    • Normal T3/T4, low TSH
    • Typically due to toxic multinodular goitre or Graves’ disease
  • Drugs
    • Amiodarone causes both hyperthyroidism and hypothyroidism
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6
Q

Pathophysiology of Graves’ disease

A
  • Anti-TSH receptor antibodies
  • Most common cause of hyperthyroidism (75%)
  • Diffuse goitre and thyroid eye signs
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7
Q

Pathophysiology of toxic multinoduar goitre

A
  • ​Iodine deficiency
  • Compensatory TSH secretion
  • Nodular goitre formation
  • Nodules become TSH-independent and over produce thyroid hormones
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8
Q

Secondary hyperthyroidism causes

A
  • Pituitary adenoma
    • ​TSH-secreting pituitary adenoma
  • Ectopic tumour
    • ​hCG-secreting tumours (eg choriocarcinoma)
  • Hypothalamic tumour
    • ​Excessive TRH secretion
    • Rare cause of hyperthyroidism
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9
Q

Risk factors for hyperthyroidism

A
  • Femal gender: particularly for Graves’ disease
  • Family history
  • Other autoimmune conditions
  • Smoking: increases risk of Graves’ eye disease
  • Trauma to the thyroid gland: including surgery
  • Drugs: eg Amiodarone
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10
Q

Symptoms of hyperthyroidism

A
  • Weight loss
  • Heat intolerance and sweating
  • Palpitations
  • Menstrual irregularity
  • Anxiety
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11
Q

Signs of hyperthyroidism

A
  • Postural tremor
  • Palmar erythema
  • Graves’ disease
    • Thyroid acropachy
    • Pretibial myxedema
    • Eye signs
      • Exophtalmos
      • Opthalmoplegia
    • Lid lag and retraction
  • Goitre
  • Hyperrelfexia
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12
Q

Which autoantibodies are present in Graves’ disease?

A
  • Anti-TSH receptor (90-100%)
  • Anti-TPO (70-80%)
  • Anti-thyroglobulin (20-40%)
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13
Q

Primary investigations in hyperthyroidism

A
  • Thyroid function tests (TFTs): first line investigation
  • Antibodies: anti-TSH receptor antibodies (95%) and anti-TPO most often raised in Graves’ disease
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14
Q

Causes of disease if:

TSH low, T4 high

TSH low, T4 normal

TSH high/normal, T4 high

A
  • TSH low, T4 high: primary hyperthyroidism
  • TSH low, T4 normal: sub clinical hyperthyroidism
  • TSH high/normal, T4 high: secondary hyperthyroidism
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15
Q

Investigations to consider in hyperthyroidism

A
  • Ultrasound: if thyrotoxic with a palpable thyroid nodule
  • Technetium radionuclide scan: performed if anti-TSH antibodies are negative
  • Glucose: hyperthyroidism is associated with hyperglycaemia
  • ECG: hyperthyroidism is associated with atrial fibrillation
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16
Q

Management of hyperthyroidism

A
  • Anti thyroid medication
    • Carbimazole: usually first line
    • Propylthiouracil: first line pre-pregnancy or in the first trimester
    • Titration regime: titration down to lowest effective dose
    • Block and replace regimen: levothyroixine is added as needed
  • Radioiodine
    • First line definitive management in more-than-mild Graves’ and toxic multinodular goitre
  • Surgery: total or hemithyroidectomy
    • Requires pre-operative optimisation (aiming for euthyroidism)
  • Consider propranolol for symptomatic relief
17
Q

Contraindications for radioiodine therapy

A
  • Pregnancy and breastfeeding
  • Thyroid eye disease
  • < 16 years
18
Q

Advice for patients post radioiodine treatment

A
  • Avoid close contact with pregnant women and children for 3 weeks
  • Avoid becoming pregnancy for 6 months
  • Avoid fathering children for 4 months
  • Patients will often require long term levothyrxine after radioiodine therapy
19
Q

Indication for total or hemithyroidectomy

A

Indicated in those at high risk of recurrent hyperthyroidism or when other options fail.

Hemithyroidectomy is preferred for a single thyroid nodule.

20
Q

Complications of thyroidectomy

A
  • Hypothyroidism
  • Hypoparathyroidism
  • Recurrent laryngeal nerve palsy
21
Q

Complications of hyperthyroidism

A
  • Cardiovascular: heart failure, atrial fibrillation
  • Musculoskeletal: osteoporosis, proximal myopathy
  • Thyrotoxic crisis
  • Iatrogenic:
    • Agranulocytosis and neutropaenic sepsis: secondary to carbimazole
    • Hepatotoxicity: secondary to propylthiouracil
    • Congenital malformations: carbimazole in first trimester
    • Foetal goitre and hypothyroidism: any anti thyroid medication in pregnancy at high doses
22
Q

Thyroiotoxic crisis (thyroid storm) aetiology

A
  • Untreated hyperthyroidism
  • Often triggered by an infection
23
Q

Thyroid storm clinical features

A
  • Tachycardia: often >140 BPM, with or without AF
  • High temperature: often > 40 degrees
  • Diarrhoea and vomiting
  • Jaundice
  • Confusion or mental agitation
24
Q

Thyroid storm mortality rate

A
  • With treatment: 20-40%
  • Untreated: up to 75%
25
Q

Investigations for thyroid storm

A
  • TFTs: elevated T3 and T4, suppressed TSH
  • Screen for the cause: eg an infection screen
  • Full set of bloods: FBC, U&Es, LFTs, bone profile, blood glucose
  • CXR
  • Arterial blood gases
26
Q

Management of thyroid storm

A
  • IV fluids: replace losses
  • NG tube insertion: if vomiting
  • Cooling: sponging and paracetamol
  • Antithyroid drugs: propylthiouracil is often preferred
  • Corticosteroid: IV hydrocortisone
  • Beta-blocker: propranolol PO or IV over 10 minutes
  • Oral iodine: Lugol’s iodine offered >1 hour after propylthiouracil
  • Sedation: if required, use chlorpromazine
  • Plasma exchange or thyroidectomy: in refractory patients

4th Year Endocrinology (7 decks)

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