Hypothyroidism: An Introduction to a Common Disorder

Audrey is a 50-year old middle school teacher. She lives an active and healthy lifestyle, eating healthy and exercising regularly. Until several months ago, she had been in excellent physique. Lately, Audrey has noticed that her skin is becoming drier. She gets tired more easily without any major changes in her daily routines. Furthermore, she gets constipated from time to time. What bothered her most was significant weight gain despite her continued exercise and healthy diet. Alarmed by these changes, she came to the hospital to seek medical consultation. After a thorough physical exam, her doctor suspected Audrey may have an underactive thyroid, or hypothyroidism, and ordered thyroid function tests.

What is hypothyroidism?

Hypothyroidism is a common disorder in which the thyroid gland can not produce enough hormones to meet the body’s demand. It is much more prevalent in women than in men. The thyroid gland is a butterfly-shaped gland located in the lower front of the neck, and is normally controlled by a gland in the brain known as the pituitary. When the pituitary releases thyroid stimulating hormone (TSH), the thyroid secretes two kinds of hormones – triiodothyronine (T3) and thyroxine (T4) – into the blood stream. The thyroid hormones help the body work properly by controlling the rate of metabolism and functions of many organ systems. When hypothyroidism occurs, the body’s metabolism slows down, potentially leading to many symptoms including:

• Cool, dry, pale skin with decreased sweating
• Hair loss and coarse hair
• Thin and brittle nails
• Puffy eyes due to swelling of the eye lids
• Anemia
• Fatigue
• Decreased heart rate
• Decreased exercise capacity
• Cold intolerance
• Constipation
• Weight gain
• Menstrual irregularity, infertility and miscarriage in women; erectile dysfunction and decreased libido in men
• Cognitive impairment, memory loss
• Joint pain
• Muscle weakness

What are the causes of hypothyroidism?

Ninety-five percent of all hypothyroid cases are caused by problems in the thyroid itself, and are classified as primary hypothyroidism. People with autoimmune diseases, such as type 1 diabetes, or a family history of thyroid disease are at increased risk of developing hypothyroidism. In rare cases, problems in specific regions of the brain – the pituitary and hypothalamus – decrease the release of TSH, resulting in diminished secretion of thyroid hormones. Primary hypothyroidism can be caused by many factors such as:

• Iodine intake: The thyroid gland requires a proper amount of iodine to function. Iodine deficiency is the most common cause of hypothyroidism worldwide although too much iodine can also lead to hypothyroidism.
• Autoimmune disease: In iodine-sufficient countries, hypothyroidism is most commonly caused by autoimmunity, where the immune system mistakenly recognizes the thyroid gland as a foreign object and attacks it. This leads to a reduced production of thyroid hormones.
• Surgical or medical treatment: Surgical removal of all or part of the thyroid and radiation therapy is often required in cases such as Graves’ disease, nodular goiter, or thyroid cancer. This can result in partial or complete loss of thyroid function. In addition, certain medications such as lithium, amiodarone and interferon alpha may also cause hypothyroidism.
• Congenital hypothyroidism: Some children are born without a thyroid gland or with a malfunctioning thyroid.
• Infectious thyroiditis: A viral infection can also cause inflammation of the thyroid gland, affecting its function.

How is hypothyroidism diagnosed?

Thyroid stimulating hormone (TSH) is the screening test for hypothyroidism. When the thyroid gland is not producing enough thyroid hormones, TSH acts as a messenger sent from the brain to instruct the thyroid to produce more hormones. An elevated TSH level suggests the thyroid gland is underactive and the test is usually repeated along with the thyroid hormone level for confirmation.

Why is it important to treat hypothyroidism?

Aside from causing a wide range of symptoms, hypothyroidism is associated with high blood cholesterol levels, specifically elevated bad cholesterol (LDL) and triglyceride levels. Heart disease and high blood pressure are also more common in people with underactive thyroid. Severe hypothyroidism can be life-threatening.

Pregnant women are recommended to have thyroid function screening. Complications associated with untreated hypothyroidism during pregnancy include preeclampsia, preterm delivery, muscle weakness, placental abnormalities, low birth weight and cognitive impairment of the infants.

How is hypothyroidism treated?

Once confirmed, the symptoms can usually be controlled by proper dosages of thyroid hormone called levothyroxine, a medication that is safe for pregnancy. Usually, the symptoms will improve within two weeks of thyroid hormone replacement therapy, although it may take several months for symptoms to completely resolve. Regular TSH retests, usually every six weeks until the test results are normal, are necessary to monitor the treatment efficacy so the right thyroid hormone dosage can be applied.

Audrey’s test results confirmed that she had hypothyroidism. Her TSH level was abnormally high while free T4 levels were low. Her pituitary was sending signals to the thyroid gland to make more hormones, yet her thyroid gland was malfunctioning. Her doctor prescribed levothyroxine to compensate for the hormone that Audrey’s thyroid could not make, and recommended a retest of the blood levels of TSH after six weeks. Although still anxious, Audrey is glad her doctor found a solution for her symptoms and is confident she is now on the road to recovery.

References:
http://www.uptodate.com

http://www.thyroid.org