What can go wrong with the Thyroid gland?

The problems of the thyroid can be divided into:

1) An over or under production of thyroid hormones
2) An enlarged thyroid (a goitre)
3) Nodules or lumps in the thyroid
4) Cancer
5) 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.

A mother with typical Derbyshire neck

A mother with typical Derbyshire neck, graded as a Grade III WHO goitre - click to enlarge

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.

Do any drugs affect Thyroid function?

There are a number of drugs that can affect thyroid function:

1. Corticosteroids
Very high doses of corticosteroids (e.g.dexamethasone) can decrease the basal production of TSH and TRH and thus decrease thyroid hormone levels.

2. Lithium Carbonate
Lithium 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. Salicylates
These drugs reduce both the uptake and release of iodine from the thyroid.

4. Sulphonamides
These drugs result in a slight decrease in the amount of thyroid hormones.

5. Amiodarone
This 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.