Hypothyroidism is the disease state caused by insufficient thyroid hormone by the thyroid gland. There are several distinct causes for chronic hypothyroidism, the most common being Hashimoto's thyroiditis and hypothyroidism following radioiodine therapy for hyperthyroidism.

The severity of hypothyroidism varies widely. Some patients are classified as "subclinical hypothyroid" when only diagnostic findings show thyroid hormone abnormalities. Others have moderate symptoms that can be mistaken for other diseases and states. Advanced hypothyroidism may cause severe complications, the most serious one of which is myxedema.

Signs and symptoms

Adults

• Slowed speech and a hoarse, breaking voice
• Impaired memory
• Increased sensitivity to heat and cold
• A slow heart rate and sluggish reflexes
• Dry puffy skin, especially on the face, and hair loss, especially thinning of the outer 1/3 of the eyebrows
• Depression (especially in the elderly)
• Weight gain and obesity
• Anemia
• Slowed metabolism
• Constipation
• Fatigue
• Choking sensation or difficulty swallowing
• Shortness of breath
• Increased need for sleep
• Muscle and joint pain
• Decreased sex drive
• Brittle fingernails
• Paleness
• Irritability
• Abnormal menstrual cycles
• Dry Skin
• Thin, fragile or absent cuticles

Children

Very Early Infancy

• Feeding problems
• Constipation
• Hoarseness
• Excessive sleepiness

Later Infancy/Toddlerhood

• Protruding abdomen
• Rough, dry skin
• Delayed teething

After Toddlerhood

• Lack of normal growth
• Abnormally short for age on height/weight charts
• Puffy, bloated appearance
• Below-normal intelligence for age

Causes

Neonatal hypothyroidism

Thyroid hormone is very important to neural development in the neonatal period. A deficiency of thyroid hormones can lead to cretinism. For this reason it is important to detect and treat thyroid deficiency early. In Australia, the Netherlands and many other countries this is done by testing for TSH on the routine neonatal heel pricks performed by law on all new born babies.

Hashimoto's thyroiditis

Sometimes called Hashimoto's Disease, this is part of the spectrum of auto-immune diseases and is related to Graves' disease, lymphocytic thyroiditis as well as other organ related auto-immune conditions such as Addison's disease, diabetes, premature menopause and vitiligo. Hashimoto's is a lymphocytic and plasmacytic thyroid inflammation that eventually destroys the thyroid. Patients require permanent thyroid replacement.

Pituitary failure

Reduction or loss of TSH secretion by the pituitary is a rare cause of hypothyroidism. This constellation is usually referred to as "secondary hypothyroidism". Even rarer is tertiary hypothyroidism that is caused either by hypothalamic lesions or by interruption of signal transfer in the portal veins connecting the hypothalamus to the pituitary gland (Pickardt syndrome).

Iatrogenic

Hypothyroidism may occur as an adverse reaction to lithium used in the treatment of mood disorders, and in response to interferon and IL-2 treatment (e.g. for cancer). It may also be a result of the antiarrhythmic amiodarone.

Surgery on the thyroid is generally done in a form that allows some hormone-producing tissue to remain. Nevertheless, some patients will need hormone supplementation after surgery.

Treatment

Substitution of thyroid hormones by taking thyroxine (T4) tablets, usually in the form of levothyroxine. Doses are started with smaller amounts of thyroxine and then slowly titrated under control of TSH levels. Usually the maintenance dose is about 1 to 2 micrograms (µg) per kilogram of body weight.

Controversy exists about the usefulness of administrating triiodothyronine (T3) as well as T4. Generally, the liver converts T4 to T3.

Deficiencies of some dietary minerals and iodine can lead to hypothyroidism. Supplementation can be an effective treatment.

See also

• hyperthyroidism

External link

• DMOZ