Disorders of Thyroid Function - Quick Reference

• This is a Quick Reference article. See also the main articles Examining a patient with thyroid complaint Examining a Patient with a Thyroid Complaint, Hypothyroidism Hypothyroidism and Hyperthyroidism Hyperthyroidism.

Examination

• Symptoms
  • In hypothyroidism: fatigue, constipation, feeling cold, slow heart rate, impaired memory
  • In hyperthyroidism: sweating, feeling hot, fatigue, muscle weakness, deteriorating physical fitness, palpitations, tremor, diarrhoea, weight loss, thirst, irritability, sleeplessness
• History (medication, family)
• Palpation (the size and consistency of the thyroid gland, nodules, tenderness)
• Initial investigations serum TSH, free T4 (FT4)
• Additional investigations
  • Free T3 (FT3) if hyperthyroidism is suspected (low TSH) but FT4 is normal
  • Thyroid peroxidase (TPO) antibodies, if the diagnosis of autoimmune thyroiditis would assist the treatment assessment

Hypothyroidism

• TSH high, FT4 below reference range
  • Subclinical: FT4 within reference range
• Permanent
  • Primary (95%): autoimmune thyroiditis Chronic Autoimmune Thyroiditis (TPO antibodies high), following surgery or radio-iodine therapy
  • Central (5%): TSH normal or low, FT4 low
• Transient
  • Subacute thyroiditis Subacute Thyroiditis
  • Drug induced (lithium, amiodarone)
• Thyroxine replacement therapy
  • Usual maintenance dose 100 µg/day
  • Starting dose in young patients 50-100 µg/day, in elderly and those with multiple diseases 25 µg/day
  • Treatment is adjusted individually according to general health and laboratory values. Laboratory tests not to be repeated until 2 months after dose changes.

Hyperthyroidism

• TSH low, FT4 and/or FT3 above reference range
  • Subclinical: TSH below reference range, FT4 and FT3 normal
• Causes
  • Basedow's disease (Graves' disease; the most common, TSH receptor antibodies high, sometimes eye symptoms Graves' Ophthalmopathy)
  • Multinodular goitre
  • Adenoma
  • Drugs: overdosage of thyroxine, iodine-containing substances
• Treatment is started in primary health care with a beta-blocker or an antithyroid drug.
• The actual treatment strategy is decided on in specialised care
  • Long-term antithyroid therapy (small gland, eye symptoms; note the risk of agranulocytosis)
  • Surgery (large gland, multinodular goitre; carried out in the euthyroid state; thyroidectomy leads to permanent hypothyroidism)
  • Radioiodine (small gland, patient in good general health; may worsen eye symptoms, often leads to permanent hypothyroidism)
• Symptomatic treatment with a beta blocker