Hypothyroidism
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Template:DiseaseDisorder infobox-Template:ICD9 | }} Hypothyroidism is the disease state caused by insufficient production of 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. Patients are classified as "subclinical hypothyroid" if diagnostic findings show thyroid hormone abnormalities, but they do not exhibit any symptoms. 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.
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Signs and symptoms
Adults
- Slowed speech and a hoarse, breaking voice. Deepening of the voice can also be noticed.
- Impaired memory
- 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 1/3 of the eyebrows
- Depression (especially in the elderly)
- Weight gain and obesity
- 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)
- 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
- Decreased sex drive
- Brittle fingernails
- Paleness
- Irritability
- Abnormal menstrual cycles
- Impaired renal function with decreased GFR.
- Thin, fragile or absent cuticles
- Infertility or difficulty becoming pregnant
- Elevated serum cholesterol
- Acute psychosis (myxedema madness) is a rare presentation of hypothyroidism
Children
Very Early Infancy
- Feeding problems
- Constipation
- Hoarseness
- Excessive sleepiness
- Protruding tongue
- Puffy appearance of hands and feet
- Deaf mutism
Later Infancy/Toddlerhood
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 newborn babies.
Hashimoto's thyroiditis
Sometimes called Hashimoto's Disease, this is part of the spectrum of autoimmune diseases and is related to Graves' disease, lymphocytic thyroiditis, and other organ-related autoimmune 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 hormone replacement.
Autoimmune hypothyroidism may also be part of a spectrum of disorders referred to as Schmidt's syndrome:
- Hypothyroidism
- Pernicious anemia
- Diabetes mellitus
- Adrenal insufficiency
In the past, surgery on the thyroid was generally done in a form that allows some hormone-producing tissue to remain. However, since the amount of thyroid tissue to leave behind was based mostly on guesswork, most surgeons choose to remove the entire thyroid and supplement the patient with a daily oral dose of thyroid hormone.
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.
Iodine deficiency
Severe iodine deficiency is another major cause of hypothyroidism. In areas of the world where there is an iodine deficiency in the diet, severe hypothyroidism can be seen in 5 to 15% of the population. In many countries, iodine deficiency is very rare due to the small amount of iodine salt that is added to common table salt.
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.
- During the 1950s synthetic thyroxine became available and gradually replaced the long used Armour Thyroid which is created from desiccated pig thyroid glands and contains a ratio of three parts T4 to one part T3. These drugs were never FDA tested and grandfathered in. In the late 90s when the FDA did require them to be tested many of them failed and there is much controversy over their approval. One big problem is that many of them were initially tested on male medical students and females typically have a very different response due to poor T3 conversion (the body converts T4 into T3). T3 is the active form of thyroxine and several organs including the liver, kidneys and brain require T3 directly to function. Proponents of the synthetics argue that the liver converts T4 to T3 naturally however most of these tests were done in men and often women and many others show poor conversion rates. Proponents for the new synthetics argued they were more stable although this was never proven nor tested. Worse, administering T4 to a patient who is having conversion problems can actually block the use and absorption of available T3. Patients who do not respond to a T4 based product such as Levoxyl are switched to a T3 containing regimen such as Armour Thyroid and show improvement. Since T3 rapidly breaks down in the blood stream another strategy is to take Armour Thyroid in divided doses 4 times a day or to add Cytomel(synthetic T3) in a fractional dose throughout the day (often 10mg suffices, broken into 4 pieces). Supplementing with T3 is very effective in overweight patients as T3 further breaks down into T2 which has been shown to be essential in fat metabolism and T2 is often taken by body builders to lose fat.
Management of myxedema coma: It is a medical emergency. The major electrolyte imbalance are hypoglycemia, hyponatremia, hypothermia, renal failure. The initial management includes warming the patient, monitoring the vitals. Parenteral steroids is the initial drug (injection hydrocortisone 100 mg - 200 mg) given. Thyroxine 600 micrograms is given through nasogastric tube or parenteral route.
- Deficiencies of some dietary minerals and iodine can lead to hypothyroidism. Supplementation can be an effective treatment, but only if iodine deficiency has been documented, which is very rare in the Western world.