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Hypothyroidism

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What is Hypothyroidism

Hypothyroidism causes underactivity of the thyroid gland. It may be primary from disease of the thyroid gland or secondary to hypothalamic-pituitary axis.

Statistics on Hypothyroidism

  • Spontaneous hypothyroidism is infrequent with a prevalence of 1-2% and occurs more commonly in women (8-10 times).
  • Atrophic (autoimmune) hypothyroidism: six times more common in females.
  • Incidence increases with age.
  • Hashimoto’s thyroiditis: more common in females and in late middle age.

Risk Factors for Hypothyroidism

  • Autoimmune disease (Hashimoto’s thyroiditis): Autoimmune disorders occur when your immune system produces antibodies that attack your own tissues, as is the case in Hashimoto’s thyroiditis. Sometimes this process occurs within the thyroid gland. It is still unclear as to why the body produces antibodies against its own tissues. A genetic flaw is a valid suggestion, but one that is yet to be proven
  • Treatment with radioactive iodine: The most common treatment for people who produce too much thyroid hormone (hyperthyroidism) is radioactive iodine. Sadly on many occasions this form of treatment can have the effect of curing a person of their over active thyroid and leave them with an under active one.
  • Radiation therapy: Radiation used to treat cancers of the head and neck can affect your thyroid gland and may lead to hypothyroidism.
  • Thyroid surgery: Removing all or a large portion of your thyroid can diminish or halt it capability to produce hormones. Thyroid hormone treatment would then have to be taken for life.
  • Medications: A number of medications can contribute to hypothyroidism. One of the most common is lithium, which is used to treat certain psychiatric disorders.

On rare occasions the following may lead to hypothyroidism:

  • Congenital disease: Approximately one in 3,000 babies in the United States is born with a defective thyroid gland or no thyroid gland at all.
  • Iodine deficiency: The trace mineral iodine ? found primarily in seafood, seaweed, plants grown in iodine-rich soil and iodized salt ? is essential for the production of thyroid hormones.
  • Pregnancy: Some women develop hypothyroidism during or after pregnancy (postpartum hypothyroidism), often because they produce antibodies to their own thyroid gland. Left untreated, hypothyroidism increases the risk of miscarriage, premature delivery and preeclampsia– a condition that causes a significant rise in a woman’s blood pressure during the last three months of pregnancy. It can also seriously affect the developing fetus.
  • Pituitary disorders: About 1 percent of cases of hypothyroidism are caused by the failure of the pituitary gland to produce enough TSH – usually due to a benign tumor of the pituitary gland.

How is Hypothyroidism Diagnosed?

  • Full blood count: anaemia
  • Liver function tests: increased serum aspartate transferase levels
  • Urea and electrolytes: due to an increase in ADH and impaired free water clearance
  • Creatine Kinase: increased levels associated with myopathy.
  • Lipids: hypercholesterolaemia.

Prognosis of Hypothyroidism

In most patients older than 3 years, the signs and symptoms of hypothyroidism are reversed with thyroid hormone treatment.

How is Hypothyroidism Treated?

Replacement therapy with thyroxine: required for life. Assess clinically and by thyroid function tests after six weeks on a steady dose. Dose should be lower if co-existant ischaemic heart disease.

Hypothyroidism References

  1. Braunwald, Fauci, Kasper, Hauser, Longo, Jameson. Harrison’s Principles of Internal Medicine. 15th Edition. McGraw-Hill. 2001
  2. Cotran, Kumar, Collins 6th edition. Robbins Pathologic Basis of Disease. WB Saunders Company. 1999.
  3. Hurst JW (Editor-in-chief). Medicine for the practicing physician. 4th edition Appleton and Lange 1996.
  4. Kumar P, Clark M. CLINICAL MEDICINE. WB Saunders 2002 Pg 427-430.
  5. Longmore M, Wilkinson I, Torok E. OXFORD HANDBOOK OF CLINICAL MEDICINE. Oxford Universtiy Press. 2001
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Dates

Posted On: 7 September, 2003
Modified On: 30 September, 2015

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