Thyrotoxicosis The term thyrotoxicosis is retained because hyperthyroidism, i.e. symptoms due to a raised level of circulating thyroid hor- mones, is not responsible for all manifestations of the disease. Clinical types are:
● diffuse toxic goitre (Graves’ disease);
● toxic nodular goitre;
● toxic nodule;
● hyperthyroidism due to rarer causes.
Diffuse toxic goitre
Graves’ disease, a diffuse vascular goitre appearing at the same time as hyperthyroidism, usually occurs in younger women and is frequently associated with eye signs. The syndrome is that of primary thyrotoxicosis (Figure 50.17); 50% of patients have a family history of autoimmune endocrine diseases. The whole of the functioning thyroid tissue is involved, and the hypertrophy and hyperplasia are due to abnormal TSH-RAb that bind to TSH receptor sites and produce a disproportion- ate and prolonged effect.
Toxic nodular goitre
A simple nodular goitre is present for a long time before the hyperthyroidism, usually in the middle-aged or elderly, and very infrequently is associated with eye signs. The syndrome is that of secondary thyrotoxicosis. In many cases of toxic nodular goitre, the nodules are inactive, and it is the internodular thyroid tissue that is over- active. However, in some toxic nodular goitres, one or more nodules are overactive and here the hyperthyroidism is due to autonomous thyroid tissue as in a toxic adenoma.
A toxic nodule is a solitary overactive nodule, which may be part of a generalised nodularity or a true toxic adenoma. It is autonomous and its hypertrophy and hyperplasia are not due to TSH-RAb. TSH secretion is suppressed by the high level of circulating thyroid hormones and the normal thyroid tissue surrounding the nodule is itself suppressed and inactive.
The normal thyroid gland consists of acini lined with flat- tened cuboidal epithelium and filled with homogeneous col- loid (Figure 50.2). In hyperthyroidism (Figure 50.18), there is hyperplasia of acini, which are lined by high columnar epi- thelium. Many of them are empty, and others contain vacuo- lated colloid with a characteristic ‘scalloped’ pattern adjacent to the thyrocytes.