Hypothyroidism

Randi Schutz

The Thyroid

• Gland that regulates metabolism • Located in the front of the neck just below the voice box (larynx) • The thyroid gland releases two hormones: thyroxine (T4) and triioxdothyronine (T3) • The thyroid gland, as well as the pituitary gland and hypothalamus, control how much of these hormones are produced • There are three types of hypothyroidism: primary, secondary, and tertiary

Primary Hypothyroidism

• Due to a defect in the gland, the thyroid cannot make enough T3 and T4 • The most common cause of primary hypothyroidism in the United States is the destruction of the thyroid gland by the immune system (Hashimoto’s thyroiditis) • Other causes of primary hypothyroidism include: – certain drugs such as lithium – radiation exposure to the neck – radioactive iodine used for treatment of hyperthyroidism – special x-ray dyes – surgical removal of part or all of the thyroid gland – some women develop after pregnancy (postpartum thyroiditis)

Secondary & Tertiary Hypothyroidism

• In secondary hypothyroidism the thyroid gland produces too little hormone due to disorders of the pituitary gland (i.e. pituitary hypothyroidism) • Tertiary hypothyroidism is caused by disorders of the hypothalamus

Risk Factors

• Age (older than 50) • Female gender • Obesity • Thyroid surgery • X-ray or radiation treatments to the neck

Early Symptoms

• Cold intolerance • Constipation • Depression • Fatigue • Weakness • Muscle or joint pain • Paleness • Thin, brittle hair and fingernails • Dry, itchy skin • Weight gain and water retention

Late Symptoms

• Decreased sense of taste and smell • Dry flaky skin • Hoarseness • Menstrual disorders • Puffy face, hands, and feet • Slow speech • Thickening of skin • Thinning of eyebrows

Exams and Tests

• Physical examination may reveal: – Smaller than normal thyroid gland (but sometimes may also be normal in size or enlarged) – Coarse facial features – Firm swelling of arms and legs – Loss of the edges of eyebrows – Low blood pressure – Slow heart rate – Low temperature – Pale, yellow, and dry skin – Slow muscle relaxation when reflexes are tested – Thin, brittle hair • Chest x-ray may show enlarged heart

More Exams and Tests

• Laboratory tests include: – High levels of thyroid stimulating hormone (TSH) indicate that the thyroid is not producing sufficient levels of thyroid hormone (mainly T4). TSH does not diagnose secondary and tertiary hypothyroidism.

– Low free T3 and T4 – Total T3 and T4 – Anemia on a complete blood count – Increased cholesterol levels – Increased liver enzymes – Increased serum prolactin – Low serum sodium

Treatment

• Treatment is to replace the thyroid hormone that is lacking – T4 is used most often, but a combination of T4 and T3 is also used – Receive the lowest dose that relieves symptoms and brings blood tests to a normal range • Periodic monitoring of TSH levels Requires life-long therapy, can be completely controlled with early treatment

Related Complications

• Myxedema coma, the most severe from of hypothyroidism (rare) – Signs and symptoms include: low temperature, decreased breathing, low blood pressure, low blood sugar, and unresponsiveness • Depression • Heart disease • Increased risk for infection • Infertility • Miscarriage • Pituitary tumors • Complications from too much thyroid hormone replacement: – Atrial fibrillation – Osteoporosis – Symptoms of hyperthyroidism

References

Holt, Elizabeth H. "Hypothyroidism - primary."

Medline Plus

N.p., 17 June 2008. Web. 4 Dec. 2009. . "Hypothyroidism." f>.

American Association of Clinical Endocrinologists

N.p., 2006. Web. 4 Dec. 2009.

"Hypothyroidism."

Wikipedia

N.p., 21 Nov. 2009. Web. 3 Dec. 2009. .

Simon, Harvey. "Hypothyroidism."

University of Maryland Medical Center

N.p., 21 May 2009. Web. 4 Dec. 2009. .