Hypothyroidism

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**Hypothyroidism**
*Classification & external resources*

Triiodothyronine, the most active form of thyroid hormone
ICD-10	E 03.9
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.

1 Causes
2 Presentation
3 Signs and symptoms
4 Diagnostic testing
5 Treatment
6 External links
7 References

[edit] Causes

There are several distinct causes for chronic hypothyroidism in human beings. Historically, iodine deficiency was the most common cause of hypothyroidism world-wide. The disease may also be caused by a lack of thyroid gland or a deficiency of hormones from either the hypothalamus or the pituitary.

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]}

It is claimed by some in the water fluoridation controversy that hypothyroidism is related to fluoride.^{[citation needed]}

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

It 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.

[edit] Presentation

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.

[edit] Signs and symptoms

Hypothyroidism has been called the "great imitator" for the vast number of medical conditions it can mimic:

"Thyroid hormones are essential and primary regulators of the body's metabolism. Imbalances can affect virtually every metabolic process in the body, exerting significant effects on mood and energy level. Thyroid function has a profound impact on overall health via its modulation of carbohydrate, protein, and fat metabolism, vitamin utilization, mitochondrial function, digestive process, muscle and nerve activity, blood flow, oxygen utilization, hormone secretion, sexual and reproductive health, and many other physiological parameters." ^[4]

Conversely, sometimes other conditions can be mistaken for Hypothyroidism.

[edit] General psychological associations

Hypothyroidism can be caused by the medication Lithium which is used to treat Bipolar Disorder (previously known as Manic Depression).

In addition, patients with hypothyroidism and psychiatric symptoms may be diagnosed with:^[5]

atypical depression (which may present as dysthymia)
bipolar spectrum syndrome (including bipolar depression, manic-depression, mixed mania, rapid-cycling bipolar disorder, cyclothymia, and premenstrual syndromes)
borderline personality disorder
psychotic disorder (typically, paranoid psychosis)
inattentive ADHD or more specifically sluggish cognitive tempo

[edit] Adults

In adults, hypothyroidism is associated with the following:^[6]

Slowed speech and a hoarse, breaking voice. Deepening of the voice can also be noticed.
Impaired memory
Impaired cognitive function (brain fog)
Urticaria (hives)
Migraine headache
Increased sensitivity to heat and cold
A slow heart rate with ECG changes including low voltage signals. Diminished cardiac output and decreased contractility.
Pericardial effusions may occur.
Sluggish reflexes
Dry puffy skin, especially on the face, and hair loss, especially thinning of the outer third of the eyebrows
Depression (especially in the elderly)
Mild weight gain
Anemia caused by impaired hemoglobin synthesis (decreased EPO levels), impaired intestinal iron and folate absorption or B12 deficiency from pernicious anemia
Slowed metabolism
Constipation
Fatigue (physical)
anxiety/panic attacks
Choking sensation or difficulty swallowing
Shortness of breath with a shallow and slow respiratory pattern.
Impaired ventilatory responses to hypercapnia and hypoxia.
Increased need for sleep
Muscle cramps and joint pain
Brittle fingernails
Osteopenia or Osteoporosis
Paleness
Irritability
Yellowing of the skin due to impaired conversion of beta-carotene to vitamin A
Abnormal menstrual cycles (Specifically Menorrhagia)
Impaired renal function with decreased GFR.
Thin, fragile or absent cuticles
Infertility or difficulty becoming pregnant
Elevated serum cholesterol
Mood instability
Acute psychosis (myxedema madness) is a rare presentation of hypothyroidism
Poor muscle tone (muscle hypotonia)
Decreased libido
Inattentiveness

[edit] Pediatric

Hypothyroidism in pediatric patients can cause the following additional symptoms:

[edit] 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 minimum blood testing:

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

[edit] Treatment

Main article: Medical use of thyroid hormones

A doctor can perform a blood test to see if a patient suffers from hypothyroidism. A synthetic thyroid supplement can be prescribed, which the patient must take daily to replace the missing hormone. The American Thyroid Association cautions against taking herbal remedies, and warns that taking too much iodine can actually worsen both hypothyroidism and hyperthyroidism.^[3]

Patients with psychiatric symptoms (mood or psychosis) and physical symptoms of hypothyroidism, with subclinical hypothyroidism (normal TSH but low free T3) are often treated with thyroid supplement to bring the free T3 levels into the upper range of normal.