How does Thyrotoxicosis present?

The symptoms are:

  • Irritability
  • Weight loss in 90% cases, weight gain in 10%
  • Heat intolerance
  • Sweating
  • Fast or irregular heart rate
  • Vomiting or diarrhoea
  • Irregular periods and infertility
  • A fine tremor with possible muscle weakness (unable to climb stairs)
  • Heart failure in the elderly
  • Fever
  • Eye disease: called thyroid associated ophthalmopathy (TAO)
  • Skin lesions: thick like orange peel, common over the shins (pretibial myxoedema)
  • In children: behavioural disorders.

How is Thyrotoxicosis diagnosed?

Modern assays combined with clinical suspicion make the diagnosis relatively easy. The following tests should be performed:

1) Thyroid Stimulating hormone (TSH)

If this is low it confirms hyperthyroidism, as long as the free thyroxine (T4) is raised. Low TSH levels will also occur in patients with pituitary failure but then the T4 is also low. Rarely the T4 is normal in thyrotoxicosis and only free triiodothyronine (T3) is secreted highlighting the importance in measuring T3. This latter condition is called T3 toxicosis.

2) A Radioactive Iodine or Technetium Scan

Uptake of tracer doses of technetium or iodine is an essential test and may show the following:

A thyrotoxic scan

A thyrotoxic scan - click to enlarge


A low uptake or no uptake in the thyroid occurs in:

  • Thyroiditis
  • Post-partum thyroiditis
  • Iodine induced thyrotoxicosis
  • Factitious hyperthyroidism (self administered or over replacement of thyroid)

A diffuse uniform uptake in the thyroid occurs in:

  • Graves' disease.

A patchy uptake in the thyroid occurs in:

  • Toxic nodular goitre.

A solitary hot spot in the thyroid occurs in:

  • Plummer's disease.

The importance of the thyroid scan is that the low uptake states and Plummer's disease are treated differently from Graves' disease and toxic nodular goitre.