Hypothyroidism

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Hypothyroidism is the disease state caused by insufficient production of thyroid hormone by the thyroid gland. There are several distinct causes for chronic hypothyroidism, the most common being Hashimoto's thyroiditis and hypothyroidism following radioiodine therapy for hyperthyroidism.

The severity of hypothyroidism varies widely. Patients are classified as "subclinical hypothyroid" if diagnostic findings show thyroid hormone abnormalities, but they do not exhibit any symptoms. Others have moderate symptoms that can be mistaken for other diseases and states. Advanced hypothyroidism may cause severe complications, the most serious one of which is myxedema.

Signs and symptoms

Adults

Children

Very Early Infancy

Later Infancy/Toddlerhood

After Toddlerhood

  • Lack of normal growth
  • Abnormally short for age on height/weight charts
  • Puffy, bloated appearance
  • Below-normal intelligence for age

Causes

Neonatal hypothyroidism

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 thyroid deficiency early. In Australia, the Netherlands, and many other countries this is done by testing for TSH on the routine neonatal heel pricks performed by law on all newborn babies.

Hashimoto's thyroiditis

Sometimes called Hashimoto's Disease, this is part of the spectrum of autoimmune diseases and is related to Graves' disease, lymphocytic thyroiditis, and other organ-related autoimmune conditions such as Addison's disease, diabetes, premature menopause and vitiligo. Hashimoto's is a lymphocytic and plasmacytic thyroid inflammation that eventually destroys the thyroid. Patients require permanent thyroid hormone replacement.

Autoimmune hypothyroidism may also be part of a spectrum of disorders referred to as Schmidt's syndrome:

Thyroid surgery for this has generally been a sub-total thyroidectomy. A large reason for this is the risk of destroying the parathyroids in a total thyroidectomy. If insufficient thyroid tissue remains to produce normal requirements then supplementary thyroxine is required.

Pituitary failure

Reduction or loss of TSH secretion by the pituitary is a rare cause of hypothyroidism. This constellation is usually referred to as "secondary hypothyroidism". Even rarer is tertiary hypothyroidism that is caused either by hypothalamic lesions or by interruption of signal transfer in the portal veins connecting the hypothalamus to the pituitary gland (Pickardt syndrome).

Iatrogenic

Hypothyroidism may occur as an adverse reaction to lithium used in the treatment of mood disorders, and in response to interferon and IL-2 treatment (e.g. for cancer). It may also be a result of the antiarrhythmic amiodarone.

Iodine deficiency

Severe iodine deficiency is another major cause of hypothyroidism. In areas of the world where there is an iodine deficiency in the diet, severe hypothyroidism can be seen in 5 to 15% of the population. In many countries, iodine deficiency is very rare due to the small amount of iodine salt that is added to common table salt.


Surgery on the thyroid is generally done in a form that allows some hormone-producing tissue to remain. Nevertheless, some patients will need hormone supplementation after surgery.

Treatment

Myxedema coma

Myxedema coma is a medical emergency. The major imbalances are hypoglycemia, hyponatremia, hypothermia and acute renal failure. The initial management includes warming the patient, monitoring the vitals. Parenteral steroids is the initial drug (injection hydrocortisone 100 mg - 200 mg) given. Levothyroxine 600 micrograms is given through nasogastric tube or parenteral route.

Hypothyroidism

Clinically apparent hypothyroidism usually warrants treatment. In case the hypothyroidism is due to dietary minerals and iodine, supplementation with these may obviate the need for hormonal treatment, but only if iodine deficiency has been documented, which is very rare in the Western world. Whilst subclinical hypothyroidism is thought to have long-term consequences, such as atherosclerosis and coronary heart disease risks. There is no current consensus as to the benefits of treatment in this group.

Treatment is usually with levothyroxine (starting at 50 μg/day), a synthetic thyroxine analogue. There is no evidence suggesting that there is any need to substitute T3 as well. Symptoms as well as TSH levels are used to monitor effect of substitution; a high TSH level suggests treatment is not yet adequate and that dose adjustments are necessary. A low ("suppressed") TSH may indicate the dose is too high. Some patients prefer a pig thyroid extract, natural desiccated thyroid hormones, which contains T3 as well as T4 and traces of T2, T1 and calcitonin.

See also

External links

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