Hypothyroidism
Encyclopedia
Hypothyroidism is a condition in which the thyroid gland does not make enough 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
.
Even sub-clinical hypothyroidism can have serious consequences.
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:
there is a substantially increased need of thyroid hormones and substantial risk that an previously unnoticed, subclinical or latent hypothyroidism will turn into overt hypothyroidism.
See thyroid disease in pregnancy
for more details.
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.
Even mild or subclinical hypothyroidism are known to adversely affect fertility.
Estimates of subclinical hypothyroidism range between 3–8%, increasing with age; incidence is more common in women than in men.
, 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 stabilizer
s, 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
.
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
Weak adrenal glands can also result in hypothyroid symptoms without affecting the thyroid itself.
(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:
Additionally, the following measurements may be needed:
(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.
The 2002 Laboratory Medicine Practice Guidelines of the National Academy of Clinical Biochemistry state that during pregnancy:
"The L-T4 dose should be increased (usually by 50 mcg/day) to maintain a serum TSH between 0.5 and 2.0 mIU/L and a serum FT4 in the upper third of the normal reference interval." Doctors however often assume that if your TSH is in the "normal range", sometimes defined as high as 5.5 mIu/L, it has no effect on fertility. Healthy pregnant women however have a TSH level of around 1.O 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."
. This is still controversial and is rejected by the conventional medical establishment
.
Iodine deficiency
Iodine deficiency
Iodine is an essential trace element; the thyroid hormones thyroxine and triiodotyronine contain iodine. In areas where there is little iodine in the diet—typically remote inlandareas where no marine foods are eaten—iodine deficiency gives rise to...
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
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
or hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
. It can result from a lack of a thyroid gland or from iodine-131
Iodine-131
Iodine-131 , also called radioiodine , is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical...
treatment, and can also be associated with increased stress
Stress (biology)
Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...
.
Severe hypothyroidism in infants can result in cretinism
Cretinism
Cretinism is a condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones usually due to maternal hypothyroidism.-Etymology and use of cretin:...
.
Even sub-clinical hypothyroidism can have serious consequences.
Classification
Hypothyroidism is often classified by association with the indicated organ dysfunction (see below):| Type | Origin | Description |
|---|---|---|
| Primary | Thyroid gland | The most common forms include Hashimoto's thyroiditis Hashimoto's thyroiditis Hashimoto's thyroiditis or chronic lymphocytic thyroiditis is an autoimmune disease in which the thyroid gland is gradually destroyed by a variety of cell- and antibody-mediated immune processes. It was the first disease to be recognized as an autoimmune disease... (an autoimmune disease) and radioiodine therapy for hyperthyroidism Hyperthyroidism Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous... . |
| Secondary | Pituitary gland Pituitary gland In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold... |
Occurs if the pituitary gland does not create enough thyroid-stimulating hormone Thyroid-stimulating hormone Thyrotrophin-stimulating hormone is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid gland.- Physiology :... (TSH) to induce the thyroid gland to produce enough thyroxine and triiodothyronine. Although not every case of secondary hypothyroidism has a clear-cut cause, it is usually caused by damage to the pituitary gland, as by a tumor, radiation, or surgery. Secondary hypothyroidism accounts for less than 5% or 10% of hypothyroidism cases. |
| Tertiary | Hypothalamus Hypothalamus The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions... |
Results when the hypothalamus fails to produce sufficient thyrotropin-releasing hormone (TRH). TRH prompts the pituitary gland to produce thyroid-stimulating hormone (TSH). Hence may also be termed hypothalamic-pituitary-axis hypothyroidism. It accounts for less than 5% of hypothyroidism cases. |
Signs and symptoms
Early hypothyroidism is often asymptomatic and can have very mild symptoms. Subclinical hypothyroidism is a state of normal thyroid hormoneThyroid hormone
The thyroid hormones, thyroxine and triiodothyronine , are tyrosine-based hormones produced by the thyroid gland primarily responsible for regulation of metabolism. An important component in the synthesis of thyroid hormones is iodine. The major form of thyroid hormone in the blood is thyroxine ,...
levels, thyroxine
Thyroxine
Thyroxine, or 3,5,3',5'-tetraiodothyronine , a form of thyroid hormones, is the major hormone secreted by the follicular cells of the thyroid gland.-Synthesis and regulation:...
(T4) and triiodothyronine
Triiodothyronine
Triiodothyronine, C15H12I3NO4, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate....
(T3), with mild elevation of thyrotropin, thyroid-stimulating hormone
Thyroid-stimulating hormone
Thyrotrophin-stimulating hormone is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid gland.- Physiology :...
(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
- Cold intolerance, increased sensitivity to cold
- ConstipationConstipationConstipation refers to bowel movements that are infrequent or hard to pass. Constipation is a common cause of painful defecation...
- Weight gainWeight gainWeight gain is an increase in body weight. This can be either an increase in muscle mass, fat deposits, or excess fluids such as water.-Description:...
and water retentionWater retention (medicine)The term water retention signifies an abnormal accumulation of fluid in the circulatory system or within the tissues or cavities of the body.Water is found both inside and outside the body’s cells... - BradycardiaBradycardiaBradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...
(low heart rate – fewer than sixty beats per minute) - Fatigue
- Decreased sweating
- Muscle cramps and joint pain
- Dry, itchy skin
- Thin, brittle fingernails
- Rapid thoughtsRacing thoughtsRacing thoughts refers to the rapid thought patterns that often occur in manic, hypomanic, or mixed episodes. While racing thoughts are most commonly described in people with bipolar disorder, they are also common with anxiety disorders, such as OCD...
- DepressionDepression (mood)Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behaviour, feelings and physical well-being. Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, or restless...
- Poor muscle tone (muscle hypotonia)
- Female infertility, any kind of problems with menstrual cycles
- Hyperprolactinemia and galactorrheaGalactorrheaGalactorrhea or galactorrhoea is the spontaneous flow of milk from the breast, unassociated with childbirth or nursing.Contemporary Maternal-Newborn Nursing Care defines galactorrhea as "nipple discharge." -Causes:...
- Elevated serum cholesterol
Late
- Goiter
- Slow speech and a hoarse, breaking voice – deepening of the voice can also be noticed, caused by Reinke's EdemaReinke's EdemaReinke's edema, also known as polypoid degeneration, is the swelling of the vocal folds due to fluid collection .-Presentation:Reinke's edema causes the vocal folds to bilaterally swell giving them an uneven, sac-like appearance...
. - Dry puffy skin, especially on the face
- Thinning of the outer third of the eyebrows (sign of HertogheSign of HertogheThe Sign of Hertoghe or Queen Anne's sign is a thinning or loss of the outer third of the eyebrows, and is a sign of hypothyroidism.The sign is named for Eugene Hertoghe of Antwerp, a pioneer in thyroid function research.- Queen Anne's sign :...
) - Abnormal menstrual cycles
- Low basal body temperatureBasal body temperatureBasal body temperature is the lowest temperature attained by the body during rest . It is generally measured immediately after awakening and before any physical activity has been undertaken, although the temperature measured at that time is somewhat higher than the true basal body temperature...
- Thyroid-Related Depression
Uncommon
- Impaired memoryMemoryIn psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
- Impaired cognitive function (brain fog) and inattentiveness.
- A slow heart rateBradycardiaBradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...
with ECG changes including low voltage signals. Diminished cardiac output and decreased contractility - Reactive (or post-prandial) hypoglycemiaReactive hypoglycemiaReactive hypoglycemia, or postprandial hypoglycemia, is a medical term describing recurrent episodes of symptomatic hypoglycemia occurring within 4 hours after a high carbohydrate meal in people who do not have diabetes...
- Sluggish reflexesReflex actionA reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...
- Hair loss
- AnemiaAnemiaAnemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
caused by impaired haemoglobin synthesis (decreased EPOErythropoietinErythropoietin, or its alternatives erythropoetin or erthropoyetin or EPO, is a glycoprotein hormone that controls erythropoiesis, or red blood cell production...
levels), impaired intestinal iron and folate absorption or B12 deficiency from pernicious anemiaPernicious anemiaPernicious anemia is one of many types of the larger family of megaloblastic anemias... - Difficulty swallowing
- Shortness of breath with a shallow and slow respiratory pattern
- Increased need for sleep
- IrritabilityIrritabilityIrritability is an excessive response to stimuli. The term is used for both the physiological reaction to stimuli and for the pathological, abnormal or excessive sensitivity to stimuli; It is usually used to refer to anger or frustration....
and mood instability - Yellowing of the skin due to impaired conversion of beta-caroteneBeta-caroteneβ-Carotene is a strongly-coloured red-orange pigment abundant in plants and fruits. It is an organic compound and chemically is classified as a hydrocarbon and specifically as a terpenoid , reflecting its derivation from isoprene units...
to vitamin A (carotoderma) - Impaired renal function with decreased glomerular filtration rate
- Acute psychosis (myxedema madness) (a rare presentation of hypothyroidism)
- Decreased libidoLibidoLibido refers to a person's sex drive or desire for sexual activity. The desire for sex is an aspect of a person's sexuality, but varies enormously from one person to another, and it also varies depending on circumstances at a particular time. A person who has extremely frequent or a suddenly...
in men due to impairment of testicular testosterone synthesis - Decreased sense of taste and smell (anosmiaAnosmiaAnosmia is a lack of functioning olfaction, or in other words, an inability to perceive odors. Anosmia may be either temporary or permanent. A related term, hyposmia, refers to a decreased ability to smell, while hyperosmia refers to an increased ability to smell. Some people may be anosmic for one...
) - Puffy face, hands and feet (late, less common symptoms)
- GynecomastiaGynecomastiaGynecomastia or Gynaecomastia, , is the abnormal development of large mammary glands in males resulting in breast enlargement. The term comes from the Greek γυνή gyné meaning "woman" and μαστός mastós meaning "breast"...
- 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.Pregnancy and fertility
During pregnancyPregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
there is a substantially increased need of thyroid hormones and substantial risk that an previously unnoticed, subclinical or latent hypothyroidism will turn into overt hypothyroidism.
See thyroid disease in pregnancy
Thyroid disease in pregnancy
Thyroid disorders are prevalent in women of child-bearing age and for this reason commonly present in pregnancy and the puerperium. Uncorrected thyroid dysfunction in pregnancy has adverse effects on fetal and maternal well-being. The deleterious effects of thyroid dysfunction can also extend...
for more details.
Subclinical hypothyroidism in early pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
, compared with normal thyroid function, has been estimated to increase the risk of pre-eclampsia
Pre-eclampsia
Pre-eclampsia or preeclampsia is a medical condition in which hypertension arises in pregnancy in association with significant amounts of protein in the urine....
with an odds ratio
Odds ratio
The odds ratio is a measure of effect size, describing the strength of association or non-independence between two binary data values. It is used as a descriptive statistic, and plays an important role in logistic regression...
(OR) of 1.7 and the risk of perinatal mortality
Perinatal mortality
Perinatal mortality , also perinatal death, refers to the death of a fetus or neonate and is the basis to calculate the perinatal mortality rate. Variations in the precise definition of the perinatal mortality exist specifically concerning the issue of inclusion or exclusion of early fetal and...
with an OR of 2.7.
Even mild or subclinical hypothyroidism are known to adversely affect fertility.
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 thyroiditisHashimoto's thyroiditis
Hashimoto's thyroiditis or chronic lymphocytic thyroiditis is an autoimmune disease in which the thyroid gland is gradually destroyed by a variety of cell- and antibody-mediated immune processes. It was the first disease to be recognized as an autoimmune disease...
, or otherwise as a result of either an absent thyroid
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
gland or a deficiency in stimulating hormones from the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
or pituitary.
Factors such as iodine deficiency
Iodine deficiency
Iodine is an essential trace element; the thyroid hormones thyroxine and triiodotyronine contain iodine. In areas where there is little iodine in the diet—typically remote inlandareas where no marine foods are eaten—iodine deficiency gives rise to...
or exposure to iodine-131
Iodine-131
Iodine-131 , also called radioiodine , is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical...
from nuclear fallout
Nuclear fallout
Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...
, 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
Postpartum thyroiditis
Postpartum thyroiditis is a phenomenon observed following pregnancy and may involve hyperthyroidism, hypothyroidism or the two sequentially. It 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...
, a condition that affects about 5% of all women within a year of giving birth. The first phase is typically hyperthyroidism
Hyperthyroidism
Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...
; 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
De Quervain's thyroiditis
de Quervain's thyroiditis, can also be known as subacute granulomatous thyroiditis or Giant Cell Thyroiditis. Males and females of all ages are affected...
, which, in turn, is often caused by having a bad flu that enters and destroys part, or all, the thyroid
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
.
Hypothyroidism can also result from sporadic inheritance, sometimes autosomal
Autosome
An autosome is a chromosome that is not a sex chromosome, or allosome; that is to say, there is an equal number of copies of the chromosome in males and females. For example, in humans, there are 22 pairs of autosomes. In addition to autosomes, there are sex chromosomes, to be specific: X and Y...
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
Wolff-Chaikoff effect
The Wolff–Chaikoff effect is a reduction in thyroid hormone levels caused by ingestion of a large amount of iodine.It is an autoregulatory phenomenon that inhibits organification in the thyroid gland, the formation of thyroid hormones inside the thyroid follicle, and the release of thyroid...
. 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
Organification
Organification is a biochemical process that takes place in thyroid glands. It is the oxidation of iodide by peroxide, and then its binding to tyrosyl residues within the thyroglobulin molecule....
in the thyroid gland, decreasing hormone production. The antiarrhythmic agent
Antiarrhythmic agent
Antiarrhythmic agents are a group of pharmaceuticals that are used to suppress abnormal rhythms of the heart , such as atrial fibrillation, atrial flutter, ventricular tachycardia, and ventricular fibrillation....
amiodarone
Amiodarone
Amiodarone is an antiarrhythmic agent used for various types of tachyarrhythmias , both ventricular and supraventricular arrhythmias. Discovered in 1961, it was not approved for use in the United States until 1985...
can cause hyper- or hypothyroidism due to its high iodine content.
Hypothyroidism can be caused by lithium
Lithium pharmacology
Lithium pharmacology refers to use of the lithium ion, Li+, as a drug. A number of chemical salts of lithium are used medically as a mood stabilizing drug, primarily in the treatment of bipolar disorder, where they have a role in the treatment of depression and particularly of mania, both acutely...
-based mood stabilizer
Mood stabilizer
A mood stabilizer is a psychiatric medication used to treat mood disorders characterized by intense and sustained mood shifts, typically bipolar disorder.-Uses:...
s, usually used to treat bipolar disorder
Bipolar disorder
Bipolar disorder or bipolar affective disorder, historically known as manic–depressive disorder, is a psychiatric diagnosis that describes a category of mood disorders defined by the presence of one or more episodes of abnormally elevated energy levels, cognition, and mood with or without one or...
(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
Thalidomide
Thalidomide was introduced as a sedative drug in the late 1950s that was typically used to cure morning sickness. In 1961, it was withdrawn due to teratogenicity and neuropathy. There is now a growing clinical interest in thalidomide, and it is introduced as an immunomodulatory agent used...
.
Stress and hypothyroidism
StressStress (biology)
Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...
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
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
thus promoting autoimmunity
Autoimmunity
Autoimmunity is the failure of an organism to recognize its own constituent parts as self, which allows an immune response against its own cells and tissues. Any disease that results from such an aberrant immune response is termed an autoimmune disease...
, causing thyroid hormone resistance, and resulting in hormonal imbalances: indeed, excess estrogen
Estrogen
Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...
in the blood caused by chronic cortisol
Cortisol
Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...
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
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
. 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
Thyroid-stimulating hormone
Thyrotrophin-stimulating hormone is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid gland.- Physiology :...
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 hormoneThyroid-stimulating hormone
Thyrotrophin-stimulating hormone is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland, which regulates the endocrine function of the thyroid gland.- Physiology :...
(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
Thyroid hormone
The thyroid hormones, thyroxine and triiodothyronine , are tyrosine-based hormones produced by the thyroid gland primarily responsible for regulation of metabolism. An important component in the synthesis of thyroid hormones is iodine. The major form of thyroid hormone in the blood is thyroxine ,...
(mainly as thyroxine
Thyroxine
Thyroxine, or 3,5,3',5'-tetraiodothyronine , a form of thyroid hormones, is the major hormone secreted by the follicular cells of the thyroid gland.-Synthesis and regulation:...
(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 levothyroxineLevothyroxineLevothyroxine, also L-thyroxine, synthetic T4, or 3,5,3',5'-tetraiodo-L-thyronine, is a synthetic form of thyroxine , used as a hormone replacement for patients with thyroid problems. The natural hormone is chemically in the chiral L-form, as is the pharmaceutical agent...
(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 diseaseAutoimmune diseaseAutoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. In other words, the body actually attacks its own cells. The immune system mistakes some part of the body as a pathogen and attacks it. This may be restricted to...
s that may be damaging the thyroid gland - Serum cholesterol — which may be elevated in hypothyroidism
- ProlactinProlactinProlactin also known as luteotropic hormone is a protein that in humans is encoded by the PRL gene.Prolactin is a peptide hormone discovered by Henry Friesen...
— as a widely available test of pituitary function - Testing for anemia, including ferritinFerritinFerritin is a ubiquitous intracellular protein that stores iron and releases it in a controlled fashion. The amount of ferritin stored reflects the amount of iron stored. The protein is produced by almost all living organisms, including bacteria, algae and higher plants, and animals...
- Basal body temperature
Treatment
Hypothyroidism is treated with the levorotatory forms of thyroxineThyroxine
Thyroxine, or 3,5,3',5'-tetraiodothyronine , a form of thyroid hormones, is the major hormone secreted by the follicular cells of the thyroid gland.-Synthesis and regulation:...
(levothyroxine
Levothyroxine
Levothyroxine, also L-thyroxine, synthetic T4, or 3,5,3',5'-tetraiodo-L-thyronine, is a synthetic form of thyroxine , used as a hormone replacement for patients with thyroid problems. The natural hormone is chemically in the chiral L-form, as is the pharmaceutical agent...
) (L-T4) and triiodothyronine
Triiodothyronine
Triiodothyronine, C15H12I3NO4, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate....
(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
Desiccated thyroid extract
Desiccated thyroid or thyroid extract, refers to porcine thyroid glands, dried and powdered for therapeutic use. As an animal product, it is not suitable for use by vegetarians. Some religious dietary laws object to the use of pork products as well, although exceptions are sometimes made for...
is an animal-based thyroid extract, most commonly from a porcine
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
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.The 2002 Laboratory Medicine Practice Guidelines of the National Academy of Clinical Biochemistry state that during pregnancy:
"The L-T4 dose should be increased (usually by 50 mcg/day) to maintain a serum TSH between 0.5 and 2.0 mIU/L and a serum FT4 in the upper third of the normal reference interval." Doctors however often assume that if your TSH is in the "normal range", sometimes defined as high as 5.5 mIu/L, it has no effect on fertility. Healthy pregnant women however have a TSH level of around 1.O mIU/L.
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/LInternational unit
In pharmacology, the International Unit is a unit of measurement for the amount of a substance, based on biological activity or effect. It is abbreviated as IU, as UI , or as IE...
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
Meta-analysis
In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. In its simplest form, this is normally by identification of a common measure of effect size, for which a weighted average might be the output of a meta-analyses. Here the...
by the Cochrane Collaboration
Cochrane Collaboration
The Cochrane Collaboration is a group of over 28,000 volunteers in more than 100 countries who review the effects of health care interventions tested in biomedical randomized controlled trials. A few more recent reviews have also studied the results of non-randomized, observational studies...
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 lifeQuality of life
The term quality of life is used to evaluate the general well-being of individuals and societies. The term is used in a wide range of contexts, including the fields of international development, healthcare, and politics. Quality of life should not be confused with the concept of standard of...
. This is still controversial and is rejected by the conventional medical establishment
Scientific consensus
Scientific consensus is the collective judgment, position, and opinion of the community of scientists in a particular field of study. Consensus implies general agreement, though not necessarily unanimity. Scientific consensus is not by itself a scientific argument, and it is not part of the...
.
See also
- Subacute lymphocytic thyroiditis
- HyperthyroidismHyperthyroidismHyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...
- Adrenal insufficiencyAdrenal insufficiencyAdrenal insufficiency is a condition in which the adrenal glands, located above the kidneys, do not produce adequate amounts of steroid hormones , primarily cortisol, but may also include impaired aldosterone production which regulates sodium, potassium and water retention...
External links
- Hypothyroidism Booklet - American Thyroid Association
- A Personal Blog (Thyroid Cancer and Pheochromocytoma, MEN 2B)