5th April 2024

Hyperthyroidism/thyrotoxicosis

Affecting females more than males, several disorders can cause thyrotoxicosis, of which Grave’s disease is the commonest cause. This autoimmune disorder occurs where thyroid stimulating antibodies stimulate thyroid gland growth and thyroid hormone production. Clinical features include

• Exophthalmos and/or ophthalmoplegia
• Pretibial myxoedema
• Thyroid acropachy, which consists of digital clubbing, soft tissue swelling of hands and feet and periosteal new bone formation

Investigations

Thyroid function tests will reveal raised T3/T4 and suppressed TSH. TSH receptor antibodies are present in 90% of cases, whilst anti-thyroid peroxidase antibodies are seen in 75%. On radionuclide testing, there is increased homogenous uptake.

Management

Carbimazole is a thioamide drug used to lower thyroid hormone levels by inhibiting thyroid peroxidase. It can cause agranulocytosis and patients are counselled to seek medical advice in the event of developing an unexplained sore throat, to have their FBC checked.  There is an increased risk of congenital malformation when carbimazole is administered in the first trimester of pregnancy, where propylthiouracil is the preferred option.

Propranolol can help to control sympathomimetic symptoms of hyperthyroidism. In refractory cases, radioactive iodine or surgery should be considered. Contraindications to radioactive iodine include pregnancy, breastfeeding and uncontrolled thyroid eye disease. Pregnancy should be avoided for up to 6 months after radioactive iodine.

Other causes of hyperthyroidism and distinguishing features include:

• Toxic multinodular goitre, which is more common in elderly women, presenting with a goitre and multiple nodules. There is an absence of eye signs and thyroid acropachy. On the radioiodine uptake scan there is patchy uptake and treatment is with radioactive iodine
• De Quervain’s thyroiditis/subacute thyroiditis occurs secondary to infection. Accompanying features include malaise, fever and pain in the neck. Suppression of uptake is seen in the acute phase on radioiodine scan. Hypothyroidism usually follows
• Solitary toxic adenoma occurs when a single nodule grows on the thyroid gland causing excess thyroid hormone production. It is confirmed by the increased radionuclide uptake in the nodule and a decreased uptake in the surrounding extra nodular thyroid tissue. Management is with radioactive iodine or surgery
• Subclinical hyperthyroidism is a biochemical picture of low TSH but normal T3 and T4. It is associated with an increased risk of atrial fibrillation and decreased bone mineral density. TFTs should be repeated in these patients