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Health News, Information and Advice from a British Doctor

Underactive thyroid or ‘hypothyroidism’

The thyroid is a small gland that is situated in the front of the lower neck. It is made up of 2 lobes that straddle the wind pipe and are joined by a central ‘isthmus’. The cells of the thyroid gland produce a very important hormone called thyroxine. Thyroxine is essential for maintaining our metabolic balance and growth and having too little (or too much) can have a catastrophic impact on how we feel and may even be fatal. The amount of thyroxine produced by the thyroid gland is controlled by tiny concentrations of a chemical called ‘thyroid stimulating hormone’ or TSH that are released by the pituitary gland in the brain, into the blood stream. When the TSH hits the thyroid, thyroxine is released. The commonest cause of underactive thyroid is resistance of the thyroid gland to TSH. When this happens, the pituitary gland churns out more and more TSH to try and stimulate the gland into cooperating! This is why the first blood tests to become abnormal in hypothyroidism, are elevated levels of TSH, closely followed by a decline in the circulating thyroxine levels (T4 or T3). This ‘resistance’ can occur for several reasons, autoimmune disease (where the body’s own natural defences are directed at the thyroid cells, known as Hashimoto’s thyroidiitis), a very specific viral infection which causes painful swelling of the thyroid gland (De Quervain’s thyroiditis), certain drugs, or just general wear and tear! Just occasionally hypothyroidism can be caused by a failure of the pituitary gland to produce TSH (in which case the circulating TSH levels are low). This is fortunately rare.

The main symptoms of hypothyroidism as you might expect, are due to a <strong>general slowing</strong> of our metabolism and reduced growth rate. They include;

  • tiredness and lethargy
  • slow pulse rate
  • weight gain
  • coarsening of facial features
  • anaemia
  • absent periods in women
  • poor growth in children (the medical jargon for severely hypothyroid children was unfortunately called ‘cretinism’ – a condition that is thankfully rare!)

The treatment (as with all the glandular failures) is easy. <strong>Just replace the hormone!</strong> Thyroxine is likely to be started at a low level by your doctor, and is slowly increased depending on your blood test

Written by Dr M J Webberley, Consultant Gastroenterologist, September 2015