The problems of the thyroid can be divided into:
1) An over or under production of thyroid hormones2) An enlarged thyroid (a goitre)3) Nodules or lumps in the thyroid4) Cancer5) Disturbance of normal thyroid function by drugs.
An enlarged thyroid is called a goitre (Derbyshire neck).World wide the commonest cause of a goitre is iodide deficiency. Iodide is commest in mountainous areas and when 10% of the population have a goitre the goitre iscalled "endemic".Enlargement may be diffuse throughout the whole thyroid gland, or irregular affecting part or all of one lobe. When there are many nodules in the thyroid it is called a multinodular goitre. Thyroid swellings are usually not cancerous. Indeed in 2008there are less than one thousand three hundred reportednew cases of thyroid cancer a year in the United Kingdom.
The thyroid produces three hormones. Two of these (thyroxine and triiodothyronine) are chemical messengers secreted into the blood stream, which control the level of body activity.
Three situations may occur:
1) The thyroid secretion is normal (Euthyroid State) 2) The thyroid secretion is excessive (Hyperthyroid State also called Thyrotoxicosis) 3) The thyroid secretion is subnormal (Hypothyroid state also called Myxoedema)
Specialized cells in the thyroid (parafollicular cells) secrete a third hormone called calcitonin. The function of calcitonin is unclear but it has minor effects on calcium metabolism. Tumours of parafollicular cells are called medullary thyroid cancers.
There are a number of drugs that can affect thyroid function:
1. CorticosteroidsVery high doses of corticosteroids (e.g.dexamethasone) can decrease the basal production of TSH and TRH and thus decrease thyroid hormone levels.
2. Lithium CarbonateLithium carbonate is a commonly used drug for manic depression. This drug inhibits the release of the thyroid hormones and interferes with their peripheral deiodination.
3. SalicylatesThese drugs reduce both the uptake and release of iodine from the thyroid.
4. SulphonamidesThese drugs result in a slight decrease in the amount of thyroid hormones.
5. AmiodaroneThis is an anti-arrhythmic drug that contains iodine. This drug can have various effects on thyroid function causing both hyperthyroidism and hypothyroidism, depending on iodine levels and thyroid function.