Hypothyroidism

Hypothyroidism (pronounced ) is a condition in which the thyroid gland does not make enough thyroid hormone. (a deficiency of thyroid hormone).

Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or hypothalamus. It can result from a lack of a thyroid gland or from iodine-131 treatment, and can also be associated with increased stress.

Severe hypothyroidism in infants can result in cretinism.

Classification
Hypothyroidism is often classified by association with the indicated organ dysfunction (see below):

Signs and symptoms
Early hypothyroidism is often asymptomatic and can have very mild symptoms. Subclinical hypothyroidism is a state of normal thyroid hormone levels, thyroxine (T4) and triiodothyronine (T3), with mild elevation of thyrotropin, thyroid-stimulating hormone (TSH). With higher TSH levels and low free T4 levels, symptoms become more readily apparent in clinical (or overt) hypothyroidism.

Hypothyroidism can be associated with the following symptoms:

Early

 * Poor muscle tone (muscle hypotonia)
 * Fatigue
 * Hyperprolactinemia and galactorrhea
 * Elevated serum cholesterol
 * Cold intolerance, increased sensitivity to cold
 * Constipation
 * Rapid thoughts
 * Depression
 * Muscle cramps and joint pain
 * Thin, brittle fingernails
 * Coarse hair
 * Paleness
 * Decreased sweating
 * Dry, itchy skin
 * Weight gain and water retention
 * Bradycardia (low heart rate – fewer than sixty beats per minute)

Late

 * Goiter
 * Slow speech and a hoarse, breaking voice – deepening of the voice can also be noticed, caused by Reinke's Edema.
 * Dry puffy skin, especially on the face
 * Thinning of the outer third of the eyebrows (sign of Hertoghe)
 * Abnormal menstrual cycles
 * Low basal body temperature
 * Thyroid-Related Depression

Uncommon

 * Impaired memory
 * Impaired cognitive function (brain fog) and inattentiveness.
 * A slow heart rate with ECG changes including low voltage signals. Diminished cardiac output and decreased contractility
 * Reactive (or post-prandial) hypoglycemia
 * Sluggish reflexes
 * Hair loss
 * Anemia caused by impaired haemoglobin synthesis (decreased EPO levels), impaired intestinal iron and folate absorption or B12 deficiency from pernicious anemia
 * Difficulty swallowing
 * Shortness of breath with a shallow and slow respiratory pattern
 * Increased need for sleep
 * Irritability and mood instability
 * Yellowing of the skin due to impaired conversion of beta-carotene to vitamin A (carotoderma)
 * Impaired renal function with decreased glomerular filtration rate
 * Acute psychosis (myxedema madness) (a rare presentation of hypothyroidism)
 * Decreased libido in men due to impairment of testicular testosterone synthesis
 * Decreased sense of taste and smell (anosmia)
 * Puffy face, hands and feet (late, less common symptoms)
 * Gynecomastia
 * Deafness
 * Enlarged tongue

Subclinical hypothyroidism
Subclinical hypothyroidism occurs when thyrotropin (TSH) levels are elevated but thyroxine (T4) and triiodothyronine (T3) levels are normal. In primary hypothyroidism, TSH levels are high and T4 and T3 levels are low. TSH usually increases when T4 and T3 levels drop. TSH prompts the thyroid gland to make more hormone. In subclinical hypothyroidism, TSH is elevated but below the limit representing overt hypothyroidism. The levels of the active hormones will be within the laboratory reference ranges.

Subclinical hypothyroidism in early pregnancy, compared with normal thyroid function, has been estimated to increase the risk of pre-eclampsia with an odds ratio (OR) of 1.7 and the risk of perinatal mortality with an OR of 2.7.

Epidemiology
About three percent of the general population has hypothyroidism. A 1995 survey in the UK found the mean incidence (with 95% confidence intervals) of spontaneous hypothyroidism in women was 3.5/1000 survivors/year (2.8-4.5) rising to 4.1/1000 survivors/year (3.3-5.0) for all causes of hypothyroidism and in men was 0.6/1000 survivors/year (0.3-1.2).

Estimates of subclinical hypothyroidism range between 3–8%, increasing with age; incidence is more common in women than in men.

Causes
Iodine deficiency is the most common cause of hypothyroidism worldwide. In iodine-replete individuals hypothyroidism is frequently caused by Hashimoto's thyroiditis, or otherwise as a result of either an absent thyroid gland or a deficiency in stimulating hormones from the hypothalamus or pituitary.

Factors such as iodine deficiency or exposure to iodine-131 from nuclear fallout, which is absorbed by the thyroid gland like regular iodide and destroys its cells, can increase the risk.

Congenital hypothyroidism is very rare accounting for approximately 0.2‰ and can have several causes such as thyroid aplasia or defects in the hormone metabolism. Thyroid hormone insensitivity (most often T3 receptor defect) also falls into this category although in this condition the levels of thyroid hormones may be normal or even markedly elevated.

Hypothyroidism can result from postpartum thyroiditis, a condition that affects about 5% of all women within a year of giving birth. The first phase is typically hyperthyroidism; the thyroid then 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 result from de Quervain's thyroiditis, which, in turn, is often caused by having a bad flu that enters and destroys part, or all, the thyroid.

Hypothyroidism can also result from sporadic inheritance, sometimes autosomal recessive.

Hypothyroidism is also a relatively common disease in domestic dogs, with some specific breeds having a definite predisposition.

Temporary hypothyroidism can be due to the Wolff-Chaikoff effect. A very high intake of iodine can be used to temporarily treat hyperthyroidism, especially in an emergency situation. Although iodide is a substrate for thyroid hormones, high levels reduce iodide organification in the thyroid gland, decreasing hormone production. The antiarrhythmic agent amiodarone can cause hyper- or hypothyroidism due to its high iodine content.

Hypothyroidism can be caused by lithium-based mood stabilizers, usually used to treat bipolar disorder (previously known as manic depression). In fact, lithium has occasionally been used to treat hyperthyroidism. Other drugs that may produce hypothyroidism include interferon alpha, interleukin-2, and thalidomide.

Stress and hypothyroidism
Stress is known to be a significant contributor to thyroid dysfunction: this can be environmental stress as well as lesser-considered homeostatic stress such as fluctuating blood sugar levels and immune problems. Moreover, adrenal stress's effect on thyroid function can be indirect, through its effects on blood sugar levels (dysglycemia), but can also have more direct effects. Stress can cause hypothyroidism or reduced thyroid functioning through disrupting the HPA axis which down-regulates thyroid function, reducing the conversion of T3 to T4, weakening the immune system thus promoting autoimmunity, causing thyroid hormone resistance, and resulting in hormonal imbalances: indeed, excess estrogen in the blood caused by chronic cortisol elevations (which reduce the liver's ability to clear excess estrogen ), can result in hypothyroid symptoms by decreasing levels of active T3. Stress also affects thyroid functioning through the sympathetic nervous system. Refugees from East Germany in a 1994 study who experienced chronic stress were found to have a very high rate of hypothyroidism or subclinical hypothyroidism, although not all refugees displayed clinical or behavioral symptoms associated with this reduced thyroid functioning. TSH levels correlate positively with physiological stress.

Symptoms of adrenal stress include


 * Fatigue
 * Headaches
 * Decreased immunity
 * Difficulty falling asleep, staying asleep and waking up
 * Mood swings
 * Sugar and caffeine cravings
 * Irritability or lightheadedness between meals
 * Eating to relieve fatigue
 * Dizziness when moving from sitting or lying to standing
 * Gastric ulcers

Weak adrenal glands can also result in hypothyroid symptoms without affecting the thyroid itself.

Diagnosis
The only validated test to diagnose primary hypothyroidism, is to measure thyroid-stimulating hormone (TSH) and free thyroxine (T4). However, these levels can be affected by non-thyroidal illnesses.

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 (T3)). However, measuring just TSH fails to diagnose secondary and tertiary hypothyroidism, thus leading to the following suggested blood testing if the TSH is normal and hypothyroidism is still suspected:


 * Free triiodothyronine (fT3)
 * Free levothyroxine (fT4)
 * Total T3
 * Total T4

Additionally, the following measurements may be needed:


 * Free T3 from 24-hour urine catch
 * 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
 * Basal body temperature

Misdiagnosis is common in hypothyroidism, with many patterns of dysfunction failing to be identified by most laboratory tests: normal TSH, T3 and T4 levels are expected in many types of thyroid dysfunction, especially those associated with increased stress.

Treatment
Hypothyroidism is treated with the levorotatory forms of thyroxine (levothyroxine) (L-T4) and triiodothyronine (liothyronine) (L-T3). Synthroid is the most common name form of the pill Levothyroxine. Synthroid is also the most common pill prescribed by doctors that has the synthetic thyroid hormone in it. This medicine can improve symptoms of thyroid deficiency such as slow speech, lack of energy, weight gain, hair loss, dry skin, and feeling cold. It also helps to treat goiter. It is also used to treat some kinds of thyroid cancer along with surgery and other medicines. 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 dosing. Levothyroxine is best taken 30–60 minutes before breakfast, as some food can diminish absorption. Compared to water, coffee reduces absorption of levothyroxine by about 30 percent. Some patients might appear to be resistant to levothyroxine, when in fact they do not properly absorb the tablets - a problem which is solved by pulverizing the medication. There are several different treatment protocols in thyroid-replacement therapy:


 * T4 only: This treatment involves supplementation of levothyroxine alone, in a synthetic form. It is currently the standard treatment in mainstream medicine.


 * T4 and T3 in combination: This treatment protocol involves administering both synthetic L-T4 and L-T3 simultaneously in combination.


 * Desiccated thyroid extract: Desiccated thyroid extract is an animal-based thyroid extract, most commonly from a porcine source. It is also a combination therapy, containing natural forms of L-T4 and L-T3.

Treatment controversy
The potential benefit from substituting some T3 for T4 has been investigated, but no conclusive benefit for combination therapy has been shown.

Subclinical hypothyroidism
There is a range of opinion on the biochemical and symptomatic point at which to treat with levothyroxine, the typical treatment for overt hypothyroidism. Reference ranges have been debated as well. As of 2003, the American Association of Clinical Endocrinologists (ACEE) considers 0.3–3.0 mIU/L within normal range.

There is always the risk of overtreatment and hyperthyroidism. Some studies have suggested that subclinical hypothyroidism does not need to be treated. A 2007 meta-analysis by the Cochrane Collaboration found no benefit of thyroid-hormone replacement except "some parameters of lipid profiles and left-ventricular function." A 2002 meta-analysis looking into whether subclinical hypothyroidism may increase the risk of cardiovascular disease, as has been previously suggested, found a possible modest increase and suggested further studies be undertaken with coronary-heart disease as an end point "before current recommendations are updated."

Alternative treatments
Compounded slow-release T3 has been suggested for use in combination with T4, which proponents argue will mitigate many of the symptoms of functional hypothyroidism and improve quality of life. This is still controversial and is rejected by the conventional medical establishment.

Hypothyroidism and Diet
This condition affects the immune system and metabolism. There are a number of supplementary vitamins and minerals specifically designed to support deficiencies in both and sufferers can mistakenly take them believing them to be beneficial. However it is important that these should never be self-prescribed since they can directly impact the effectiveness of thyroxine (usually through preventing its absorption).

These are:


 * Calcium
 * Soya
 * Iron (includes Iron rich foods such as Broccoli)
 * Iodine (includes Kelp tablets)
 * Selenium (includes natural sources such as sea food)
 * Magnesium
 * Zinc
 * Caffeine

This is not a full list, and the exact impact is unknown, therefore it is important that a doctor be consulted prior to taking any supplements or changing your diet.