Hyperthyroidism

Definition/diagnostic criteria Thyrotoxicosis is the clinical manifestation of excess thyroid hormone.

Hyperthyroidism (also known as overactive thyroid) is a condition where the thyroid gland produces excessive amounts of thyroid hormone. It is confirmed by low serum thyroid-stimulating hormone (TSH) levels and elevated free T4(FT4) and/or free T3 (FT3) levels.

Primary hyperthyroidism refers to when the condition arises from the thyroid gland (e.g. Graves’ disease or a nodular goitre). Drug induced causes include amiodarone, excess levothyroxine and iodine.

Secondary causes include a pituitary adenoma or high circulating levels of human chorionic gonadotrophin (hCG).

Subclinical hyperthyroidism is diagnosed when TSH is suppressed below the normal reference range, but FT4 and FT3 concentrations are within the normal reference range.

Epidemiology The prevalence of hyperthyroidism in the UK is about 2%, with a higher incidence in women than men. Graves’ disease is the most common cause, accounting for 70-80% of cases. The condition is more prevalent between the ages of 20 and 40 years.

Diagnosis

Clinical features

Features of thyrotoxicosis include:

• Weight loss
• Increased appetite
• Heat intolerance
• Diarrhoea
• Palpitations, tremor, and anxiety
• Oligomenorrhoea or amenorrhoea
• Goitre and/or thyroid nodules
• Ophthalmopathy (in Graves’ disease)
• Tachycardia, and atrial fibrillation.

Features of Graves’ orbitopathy include excessive eye watering, double vision, change in visual acuity or colour vision, eyelid retraction or lid lag, proptosis.

Features of thyroiditis include malaise, fever, thyroid pain.

Investigations

Initial tests include TSH and free T4.

If TSH is low and FT4 or FT3 is high, hyperthyroidism is confirmed.

Subsequent tests may include free T3, thyroid-stimulating hormone receptor antibodies (TRAb) for Graves’ disease (if clinical signs of Graves or if the patient is pregnant), and a thyroid scan if malignancy is suspected.

Additional tests to consider include inflammatory markers if thyroiditis is suspected. Thyroid peroxidase antibodies (TPOAbs) should be measured if a woman is postpartum and a diagnosis of postpartum thyroiditis is suspected.

In the case of subclinical hypothyroidism TFTs should be rechecked after 3 months.

Treatment The treatment of hyperthyroidism depends on the cause, age, and comorbidities. Options include:

• Antithyroid drugs (ATDs): Carbimazole or propylthiouracil (PTU)
• Radioactive iodine therapy: First line for toxic multi-nodular goitre
• Surgery: Thyroidectomy is an option for patients with large goitres, suspicion of malignancy, or those not responding to other treatments.
• Beta-blockers, like propranolol, can be used for symptomatic relief of adrenergic symptoms

Patients should be referred to secondary care. This should be via emergency admission if there are symptoms of a thyroid storm. The referral should be urgent if a secondary cause of hyperthyroidism is suspected or via a two-week wait if malignancy is suspected.

Patients with persistent subclinical hyperthyroidism should be referred for specialist advice.

Patients with current or previous hyperthyroidism (including subclinical hyperthyroidism) who are planning a pregnancy/pregnant or patients should be referred for specialist advice.

Prognosis The prognosis of hyperthyroidism is generally good with appropriate treatment. However, complications can include cardiovascular diseases, osteoporosis, and thyrotoxic crisis if not managed timely. Graves’ disease has a recurrence rate of 20-30% post-ATD treatment, and lifelong monitoring is recommended.