The most common cause of
hyperthyroidism in Australia is
Graves disease, caused by a defect in immunoregulation in genetically predisposed individuals, leading to production of
thyroid-stimulating antibodies. Each of the three modalities of
therapy for
Graves disease--thionamide drugs, subtotal or total
thyroidectomy, and radioactive
iodine ablation--can render the patient euthyroid, but all have potential adverse effects and may not eliminate recurrences.
Hypothyroidism occurs in about 5% of the adult population; most present with "subclinical"
hypothyroidism (mild thyroid failure), characterised by raised levels of serum
thyroid stimulating hormone (TSH) but normal free
thyroxine (T(4)). The most common cause of
hypothyroidism in Australia is autoimmune
chronic lymphocytic thyroiditis, characterised by raised circulating levels of
thyroid peroxidase antibody. Symptoms and signs of
hypothyroidism are often mild or subtle and, when there is clinical suspicion, thyroid function tests are needed; if serum TSH level is raised, free T(4) and
thyroid peroxidase antibody should be measured. Replacement
therapy with
thyroxine is the cornerstone of
therapy (1.6 microg/kg lean
body weight daily, taken on an empty stomach); combination
therapy with
thyroxine and
liothyronine (T(3)) is promoted, but there is little evidence of its clinical benefit. Despite the development of highly sensitive laboratory tests, clinical assessment and judgement remain paramount