THYROID PROBLEMS

The thyroid is a small but important gland that sits in the front of the neck between the Adam's-apple and the top of the breastbone. It weighs about 20 grams and is about the size of a walnut. Its main function is to secrete thyroid hormone, which sets the pace of the body's metabolism.

Like other endocrine glands the release of thyroid hormone is part of a complex feedback system. If the thyroid is not producing enough hormone the pituitary gland at the base of the brain releases thyroid stimulating hormone (TSH) to step up production; if too much thyroid hormone is being produced TSH is suppressed. The pituitary gland itself is subject to further control from various releasing factors higher in the nervous system. Thyroid hormone, TSH and other factors can be readily measured to assist with the diagnosis and management of many thyroid conditions.

The thyroid gland needs iodine to make thyroid hormone. In areas where the soil and water is deficient in iodine the gland tends to enlarge to take up more iodine.

 An enlarged thyroid gland for whatever reason is called a goitre In days gone by, some people from Gippsland and Tasmania were known to have goitres because of iodine deficiency.

Goitres are sometimes smooth and uniform, but more frequently knobbly and irregular. Although some goitres produce too much thyroid hormone, most occur when some factor interferes with the capacity of the gland to secrete enough hormone. This may be due to depletion of iodine within the thyroid gland and perhaps an increased responsiveness to the TSH from the pituitary gland.

Occasionally the thyroid can be so large that it presses on important neck structures and causes symptoms like a hoarse voice or even breathing difficulties. Tumours or cysts in the thyroid can also cause goitres, as can a condition called thyroiditis that occurs when the thyroid gland becomes inflamed.

Thyrotoxicosis or hyperthyroidism just means an overactive thyroid gland, one that is producing too much thyroid hormone. The common symptoms are sweating, agitation and weight loss, despite a good appetite. Palpitations and irregularity of the pulse may occur, as well as symptoms of heart failure like shortness of breath. The features are those of a metabolism that is being driven along to the limit. People with thyrotoxicosis usually hate warm weather and frequently have a prominent staring appearance, due to the effect of thyroid hormone on the tissues behind the eyes. Blood tests can quickly confirm the diagnosis. Patients are usually referred to an endocrine specialist for assessment. After initial treatment with medication to control the symptoms of excessive stimulation, a decision is made about longer term treatment. This might involve either surgery to remove most of the thyroid gland, or radioactive iodine treatment to permanently reduce thyroid function. Whatever treatment is chosen, follow-up blood tests are necessary to check that years later the person does not develop signs of an underactive thyroid gland.

Myxoedema or hypothyroidism means an underactive thyroid, one that is not producing enough thyroid hormone. The features are those of a metabolism grinding to a halt. It can be quite insidious and not easy to diagnose. The main symptoms are lack of energy, constipation, hoarse voice and a marked intolerance of cold weather. There may be slow reflexes and dry skin and hair. Once the diagnosis is confirmed with various blood tests the usual treatment is lifelong replacement therapy with thyroid hormone. A small dose is used initially, especially in older patients, and the response to thyroid replacement is often dramatic. However, blood tests are necessary to check that the thyroid hormone replacement dose is adequate.

Hypothyroidism can also be present at birth; this condition used be called cretinism. If it goes unrecognized permanent brain damage can occur. These days all babies are screened for hypothyroidism shortly after birth; if hypothyroidism is present thyroid hormone replacement therapy can be commenced early with very good results.

Health Tip:
* It is quite common for hypothyroidism to develop many years after the treatment for other thyroid problems, such as thyrotoxicosis and some types of thyroiditis. If you have had previous treatment for any thyroid condition, mention it to your doctor in case a follow-up blood test is required.

Dr. Andrew Pattison: Common Consultations
North East Valley Division General Practice, Melbourne, Australia.   Disclaimer
  - Last modified: August 18, 2001