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Hypothyroidism is a pathologic state caused by insufficient secretion of thyroid hormones by the thyroid gland. There are several distinct causes for chronic hypothyroidism, most common being Hashimoto thyroiditis and postoperative or hypothyroidism following radioiodine therapy.

Severity of hypothyroidism is variable. Some patients are classified as subclinical hypothyroidism when only diagnostic findings show thyroid hormone abnormality. Others have moderate symptoms that can be mistaken for other diseases and states. Advanced hypothyroidism is easily recognized even for non-specialist.

Hypothyroidism signs and symptoms are :

In the elderly hypothyroidism is relatively common and can be easily missed. It is an important but treatable cause of depression in this age group.

Neonatal period

Thyroid hormone is very important to neural development in the neonatal period. A deficiency of thyroid hormones can lead to "Cretinism". For this reason it is important to detect and treat thryoid deficiency early. In Australia this is done by testing for TSH on the routine neonatal heel pricks performed by law on all new born babies.

Hashimoto's Thyroiditis

This is part of the spectrum of auto-immune disease and is related to Graves disease, lymphocytic thyroiditis as well as other organ related auto-immune conditions such as Addisons disease, diabetes, premature menopause and vitiligo. Hashimotos is a lymphocytic and plasmacytic thryoid inflammation that eventually destroys the thyroid. Patients require permanent thyroid replacement.

Pituitary failure

Reduction or loss of TSH secretion by the pituitary is a very rare cause of hypothyroidism.

Iatrogenic (or Doctor induced).


Substitution of thyroid hormones by taking thyroxine tablets. Doses are started with smaller amounts of thyroxine and then slowly titrated under control of TSH levels. Usually the maintenance dose is about 1-2 mcg per kilogramm of body weight.

Some thyroid deficiency is a side effect of treatment for thyroid cancer, and Graves disease.

See also : DMOZ, hyperthyroidism