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Hypothyroidism



Hypothyroidism
Classification & external resources
Triiodothyronine, the most active form of thyroid hormone
ICD-10 E03.9
ICD-9 244.9
DiseasesDB 6558
eMedicine med/1145 
MeSH D007037

Hypothyroidism is the disease state in humans and animals caused by insufficient production of thyroid hormone by the thyroid gland.

Additional recommended knowledge

Contents

Causes

There are several distinct causes for chronic hypothyroidism. Historically and, still, in many developing countries iodine deficiency is the most common cause of hypothyroidism worldwide. In present day developed countries, however, hypothyroidism is mostly caused by Hashimoto's thyroiditis, or by a lack of the thyroid gland or a deficiency of hormones from either the hypothalamus or the pituitary.

Hypothyroidism can result from postpartum thyroiditis, a condition that affects about 5% of all women within a year after giving birth. The first phase is typically hyperthyroidism. Then, the thyroid either returns to normal or a woman develops hypothyroidism. Of those women who experience hypothyroidism associated with postpartum thyroiditis, one in five will develop permanent hypothyroidism requiring life-long treatment.

Hypothyroidism can also result from sporadic inheritance, sometimes autosomal recessive. It is a relatively common disease in purebred domestic dogs as well, and can have a hereditary basis in dogs.[citation needed]

Temporary hypothyroidism can be due to the Wolff-Chaikoff effect.

Hypothyroidism is often classified by the organ of origin:[1][2]

Type Origin Description
Primary hypothyroidism thyroid gland The most common forms include Hashimoto's thyroiditis (an autoimmune disease) and radioiodine therapy for hyperthyroidism.
Secondary hypothyroidism pituitary gland Occurs if the pituitary gland does not create enough thyroid stimulating hormone (TSH) to induce the thyroid gland to create a sufficient quantity of thyroxine. Although not every case of secondary hypothyroidism has a clear-cut cause, it is usually caused when the pituitary is damaged by a tumor, radiation, or surgery so that it is no longer able to instruct the thyroid to make enough hormone[3]
Tertiary hypothyroidism, also called hypothalamic-pituitary-axis hypothyroidism hypothalamus Results when the hypothalamus fails to produce sufficient TRH.

General psychological associations

Hypothyroidism can be caused by lithium-based mood stabilizers, usually used to treat bipolar disorder (previously known as manic depression).

In addition, patients with hypothyroidism and psychiatric symptoms may be diagnosed with:[4]

Symptoms

The ability of Hypothyroidism to mimic a number of medical conditions originates in the vast functions of the thyroid hormones, which are reduced or absent in this case. The functions of thyroid hormones include modulation of carbohydrate, protein and fat metabolism, vitamin utilization, mitochondrial function, digestive process, muscle and nerve activity, blood flow, oxygen utilization, hormone secretion and sexual and reproductive health[5] to mention a few. Thus, when the thyroid hormone content gets out of balance, systems covering the whole body are affected. This is why hypothyroidism can look like other diseases. Conversely, sometimes other conditions can be mistaken for hypothyroidism.

Adults

In adults, hypothyroidism is associated with the following symptoms:[3]

Early symptoms

[6]

Late symptoms

[6]

Pediatric

Hypothyroidism in pediatric patients can cause the following additional symptoms:

Severity

The severity of hypothyroidism varies widely. Some have few overt symptoms, others with moderate symptoms can be mistaken for having other diseases and states. Advanced hypothyroidism may cause severe complications including cardiovasular and psychiatric myxedema.

Diagnostic testing

To diagnose primary hypothyroidism, many doctors simply measure the amount of Thyroid-stimulating hormone (TSH) being produced. High levels of TSH indicate that the thyroid is not producing sufficient levels of Thyroid hormone (mainly as thyroxine (T4) and smaller amounts of triiodothyronine (fT3)). However, measuring just TSH fails to diagnose secondary and tertiary forms of hypothyroidism, thus leading to the following suggested blood testing if the TSH is normal and hypothyroidism is still suspected:

  • thyroid-stimulating hormone (TSH)
  • free triiodothyronine (fT3)
  • free levothyroxine (fT4)
  • total T3
  • total T4

Additionally, the following measurements may be needed:

  • antithyroid antibodies - for evidence of autoimmune diseases that may be damaging the thyroid gland
  • serum cholesterol - which may be elevated in hypothyroidism
  • prolactin - as a widely available test of pituitary function
  • testing for anemia, including ferritin

Treatment

Both synthetic and animal-derived thyroid tablets are available and can be prescribed for patients in need of additional thyroid hormone. Thyroid hormone is taken daily, and doctors can monitor blood levels to help assure proper dosaging. The American Association of Clinical Endocrinologists recommends the use of levothyroxine (T4) as thyroid replacement. In general, desiccated thyroid hormone, combinations of thyroid hormone, or triiodothyronine should not be used for replacement therapy.[8]

The American Thyroid Association cautions against taking herbal remedies, and warns that taking too much iodine can actually worsen hypothyroidism.[3]

Subclinical hypothyroidism

A meta-analysis by the Cochrane Collaboration found no benefit except "some parameters of lipid profiles and left ventricular function".[9]

References

  1. ^ http://www.umm.edu/patiented/articles/what_causes_hypothyroidism_000038_2.htm
  2. ^ http://www.pathology.vcu.edu/education/endocrine/endocrine/pituitary/diseases.html
  3. ^ a b c American Thyroid Association (ATA) (2003). Hypothyroidism Booklet (PDF), 6. 
  4. ^ Heinrich TW, Grahm G (2003). "Hypothyroidism Presenting as Psychosis: Myxedema Madness Revisited" 5 (6): 260-266. PMID 15213796.
  5. ^ Comprehensive Thyroid Assessment. Geneva Diagnostics. Retrieved on 2007-05-21.
  6. ^ a b NLM
  7. ^ Fred D.Hofdelt, Stephen Dippe, Peter H. Forshman "Diagnosis and classification of reactive hypoglycemia based on hormonal changes in response to oral and intravenous glucose administration" The American Journal of Clinical Nutrition[1]
  8. ^ American Association of Clinical Endocrinologist. Thyroid guidelines. Endocrin Pract. 2002;8:457-469.
  9. ^ Villar H, Saconato H, Valente O, Atallah A (2007). "Thyroid hormone replacement for subclinical hypothyroidism". Cochrane database of systematic reviews (Online) (3): CD003419. doi:10.1002/14651858.CD003419.pub2. PMID 17636722.

[www.aace.com/pub/pdf/guidelines/hypo_hyper.pdf]

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hypothyroidism". A list of authors is available in Wikipedia.
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