Hypothyroidism and Goiter Sydney NSW

Hypothyroidism and Goiter - Hypothyroidism Causes Enlargement of the Thyroid

Hypothyroidism, in general, has exactly the opposite effects as those of hyperthyroidism, although it may be caused by autoimmunity as well but a kind of immunity that destroys the gland rather than stimulates it. Most of the patients first have autoimmune thyroiditis, an inflammation of the thyroid glands. This causes deterioration and eventually, fibrosis of the gland or the replacement of thyroid tissue with connective tissue. Fibrotic tissue is incapable of producing thyroid hormone and a deficiency in the hormone occurs. In most cases, an enlagement of the thyroid gland is observed.

Endemic Colloid Goiter

Around 50 milligrams of iodine are required every year for the normal functioning of the thyroid gland and for production of sufficient amounts of thyroid hormone. In some areas of the world like the Swiss Alps, the Andes, and the Great Lakes regions of the United States of America, there are less than adequate quantities of iodine in the soil for the foodstuffs to contain this yearly requirement. In the days when iodized table salt was not yet available, people from these areas developed extremely large thyroid glands called endemic goiters.

Endemic goiters develop when the lack of iodine prevents the formation of sufficient quantities of the thyroid hormones thyroxine and triiodothyronine. Because of the low concentrations of thyroid hormone, there is nothing that could inhibit the production of thyroid-stimulating hormone or TSH by the pituitary gland, which would result in the anterior pituitary gland secreting increased amounts of the hormone targeting the thyroid gland. The increased levels of TSH stimulate the thyroid gland to produce increased amounts of thyroglobulin. However, without iodine to bind to the tyrosine residues in the tyroglobulin molecule, there is still no production of hormones. This causes the thyroid gland to increase in size, sometimes to as large as 10 to 20 times its normal size.

Idiopathic Nontoxic Colloid Goiter

Similarly enlarged thyroid glands filled with colloid may also happen to people who do not have an iodine deficiency, unlike patients with endemic goiter. These people may have normal levels of thyroid hormone secretion but more often than not, the secretion of thyroid hormone is depressed like that of endemic goiter.

The exact cause for the enlargement of the thyroids of patients with iodiopathic nontoxic colloid goiter is not known. However, most of these patients do show signs of mild thyroiditis, which led to the suggestion that thyroiditis might lead to slightly lower concentrations of the hormone, which in turn could cause increase in TSH secretion and progressive growth of unaffected portions of the gland. This could explain why the thyroid glands of these patients are usually nodular, with some areas exhibiting growth while some are being destroyed by thyroiditis.

Some patients with colloid goiter exhibit abnormalities in the enzyme system that helps in the production of thyroid hormone. Some of these abnormalities are the following:

• There is a problem in the process of trapping iodine, in which the thyroid is unable to pump sufficient quantities of iodine into the thyroid cells.
• A deficiency in the peroxidase system, which renders the thyroid cells unable to oxidize iodides into the iodine state. If the iodides are not oxidized into the iodine state, they are unable to bind with the tyrosine in the thyroglobulin molecule, halting the entire process of thyroid hormone formation.
• A deficiency in the coupling of iodinated tyrosines so that thyroid hormones remain unformed.
• There is a problem in the deiodinase system, preventing the recovery of iodine from the iodinated tyrosines that are not coupled to form thyroid hormones. This will eventually lead to a deficiency in iodine.
• Some foods also contain goitrogenic substances, which can act like the anithyroid drug propylthiouracil, inducing hypothyroidism. This also leads to increased TSH stimulation of the thyroid gland, causing it to become enlarged. These goitrogenic substances may be found in some types of turnips and cabbages.

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