Hyperthyroidism occurs in approximately 2% of the community and hypothyroidism in 5-10%. There is a female to male predominance of 5:1. A family history of the thyroid dysfunction is common in affected patients.
The most common cause of hyperthyroidism is Graves' disease; a diffuse goiter with a bruit is commonly found. A nodular goiter may suggest either a toxic multinodular goiter or toxic adenoma. Subacute thyroiditis is associated with a tender asymmetrically enlarged thyroid, and patients are typically systemically unwell with fever and neck pain.
Eye lid lag and lid retraction can occur in any thyrotoxic state, but proptosis (bulging eye) is specific for Graves' disease.
Treatment of hyperthyroidism usually involves antithyroid drugs, radioactive iodine or total thyroidectomy.
Common symptoms include weight gain, fatigue, cold intolerance, depression, constipation, dry skin, muscle and joint aches and slowed mental processing. There may be bradycardia, periorbital edema, thinning of the outer third of the eyebrows, hoarse voice or goitre. Hypothyroidism is suggested if several of these features occur in combination or with recent onset.
Causes of hypothyroidism include autoimmune disease (Hashimoto's thyroiditis), congential hypothyroidism, thyroid or head and neck surgery, previous irradiation, drug treatment (e.g. lithium, interferon), pituitary or hypothalamic disease.
Primary hypothyroidism is confirmed by an elevated TSH and decreased free T4 level. Patients with autoimmune thyroid disease should have their vitamin [B.sub.12] levels measured.
Treatment of hypothyroidism involves thyroxine therapy (Eutroxsig, Oroxine). Most patients require maintenance doses of 100 to 150 [micro]g daily. Women taking thyroxine and planning pregnancy may need to increase the dose by 30% during pregnancy.
Thyroid function tests should be considered in any patient with symptoms or signs suggestive of thyroid disease and in any patient at risk of developing thyroid dysfunction.
PO Box 45, Concord West NSW 2138