is the disease state in humans and animals caused by insufficient production of
Thyroid Hormone by the
Thyroid Gland . It affects about 5% of the United Kingdom population over 60 years of age. As of 2006, more than 1% of the United Kingdom population were receiving T
4 (
Thyroxine ) replacement therapy for hypothyroidism.
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There are several distinct causes for chronic hypothyroidism. Historically and, still, in many developing countries
Iodine Deficiency is the most common cause of hypothyroidism world-wide. 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 .
Temporary hypothyroidism can be due to the
Wolff-Chaikoff Effect .
Hypothyroidism is often classified by the organ of origin:http://www.umm.edu/patiented/articles/what_causes_hypothyroidism_000038_2.htmhttp://www.pathology.vcu.edu/education/endocrine/endocrine/pituitary/diseases.html
Hypothyroidism can be caused by
Lithium -based
Mood Stabilizer s, usually used to treat
Bipolar Disorder (previously known as manic depression).
In addition, patients with hypothyroidism and psychiatric symptoms may be diagnosed with:
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The ability of Hypothyroidism to mimic a number of medical conditions originates in the vast functions of the thyroid hormones, which are 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
4 to mention some. Thus, when the thyroid hormone content gets out of balance, systems covering the whole body are affected, and that's why hypothyroidism can look like other diseases. Conversely, sometimes other conditions can be mistaken for hypothyroidism.
In adults, hypothyroidism is associated with the following symptoms:
NLM
- Slowed speech and a Hoarse , breaking voice. Deepening of the voice can also be noticed.
- Dry puffy skin, especially on the face
- Thinning of the outer third of the eyebrows
- Abnormal Menstrual Cycles
- Low Basal Body Temperature
Hypothyroidism in pediatric patients can cause the following additional symptoms:
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 .
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 Disease s 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
See Also: Thyroid hormone#Medical use of thyroid hormones
l1=Medical use of thyroid hormones
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 Thyroid Association cautions against taking herbal remedies, and warns that taking too much iodine can actually worsen both hypothyroidism and hyperthyroidism.
Some researchers would suggest that there is no benefit to treatment with the T
4 - T
3 combination therapy over the T
4 monotherapy. A
Meta-analysis of 11
Randomized Controlled Trials found no advantage with the T
4 - T
3 combination therapy over the T
4 monotherapy.
However, many of the studies involved in this meta-analysis were not properly designed. They tested the medication's effectiveness by providing the same dose of thyroid medication to each patient and by utilizing the TSH test as a measure of treatment effectiveness. Thyroid medication must be individualized to the patient, carefully observing free T4 and free T3 (not TSH, which is a diagnostic tool but not a treatment tool). Beneficial effects would not expect to be seen at doses not tailored to the individual's needs. Clinically, most physicians prescribing T3 as part or all of a hypothyroid patient's treatment find that most patients receiving T3 in fact must be on a larger dose than was administered in these studies. The meta-analysis results ought to be held in question, therefore; and the knowledgeable physician will administer T3 medication for the hypothyroid patient who continues to present with symptoms and whose free T3 level is low, or low in the range.
A
Meta-analysis by the
Cochrane Collaboration found no benefit except "some parameters of lipid profiles and left ventricular function".
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