Hypothyroidism (Underactive Thyroid) Causes, Symptoms, Diagnosis and Treatment

Hypothyroidism, also called underactive thyroid, is a thyroid disease in which not enough hormone is produced to meet the body's needs. It can cause many of bodily functions to slow down. Many conditions can cause the thyroid gland to become underactive including Hashimoto's disease, thyroiditis, congenital anomalies and certain medicines.

What is the thyroid and what does it do?

The thyroid is a small, butterfly-shaped gland in the neck just below the Adam's apple. It is a two-lobed organ weighing less than an ounce.

The thyroid gland produces two major kinds of hormones: the thyroid hormones and calcitonin.

Thyroid hormones are actually of two types, the triiodothyronine and thyroxine. They are also called T₃ and T₄ respectively. The more common of these two thyroid hormones is thyroxine.

Thyroid hormones have a major effect on metabolism, which is the way the body uses energy. Other important actions of thyroid hormones include helping in normal brain development, breathing, body temperature, normal heart and nervous system functions and menstrual cycles in women in their reproductive years.

Calcitonin, on the other hand, can affect blood calcium levels. When calcium levels in the blood increases, calcitonin is released by the thyroid to stimulate deposition of calcium in the bones.

Production of thyroid hormones is regulated by another hormone produced by the pituitary-a tiny, pea-sized gland located in the brain-called thyroid stimulating hormone (TSH).

Causes of Hypothyroidism

Several diseases and conditions can cause hypothyroidism and are discussed below.

The most common cause of hypothyroidism in the United States, according to the National Endocrine and Metabolic Diseases Information Service, is Hashimoto's disease. Also called chronic lymphocytic thyroiditis, Hashimoto's disease is a type of an autoimmune disease. An autoimmune disease is a condition in which the body's own immune system attacks normal body tissues. In Hashimoto's disease, the immune system mistakenly creates antibodies that attack normal cells of the thyroid. This can cause thyroid hormone production to be impaired

Why autoimmune diseases such as Hashimoto's disease occur still remains unclear.

Thyroiditis

Thyroiditis is the inflammation of the thyroid gland. This condition can cause stored thyroid hormone to leak out of the inflamed organ. Initially, this leakage of thyroid hormone causes a rise in blood thyroid hormone levels. This elevated thyroid hormones in the blood causes hyperthyroidism, which can last for a month or two. Most people with thyroiditis eventually develop hypothyroidism before the thyroid has completely healed.

Congenital Hypothyroidism

Congenital hypothyroidism occurs when a baby is born with an undeveloped thyroid or a thyroid that is not functioning normally. According to the Genetics Home Reference (GHR) of the National Institutes of Health (NIH), the condition affects 1 in 3,000 to 4,000 newborns.

Early detection of congenital hypothyroidism is necessary to prevent future complications including mental retardation and growth failure. A newborn screening for this condition is available in most countries.

Other causes of hypothyroidism include removal of a part or the entire thyroid through surgery, radioiodine therapy and certain medications.

Signs and Symptoms of Hypothyroidism

Symptoms of hypothyroidism may be different from person to person. Common symptoms of the condition include weakness or fatigue, puffed face, weight gain, intolerance to cold temperatures, slowed heart rate (bradycardia), thinned hair, joint and muscle pain and depression. Women who have the condition and are in their reproductive years may have heavy or irregular menstruations and impaired fertility.

Diagnosis of Hypothyroidism

It may be difficult to diagnose hypothyroidism based on symptoms alone because symptoms of the condition may be similar to other health problems. In addition to taking note of your symptoms, your doctor will also ask about your medical history and perform a thorough physical examination.

To confirm the diagnosis, your doctor may recommend several diagnostic tests, such as a thyroid stimulating hormone test, a T₄ test or a thyroid autoantibody test. Diagnostic tests may also be used to find the cause of hypothyroidism.

Treatment of Hypothyroidism

The aim of hypothyroid treatment is to bring thyroid hormone levels back to normal. Hypothyroidism is usually treated with a synthetic thyroxine, which has a similar effect as the hormone thyroxine. Dosage of the synthetic hormone will be determined by the doctor.

Once the patient has started taking the synthetic thyroid hormone, regular testing of TSH levels is important. This will help the doctor determine if changes to the dose is necessary.

Sources:

Thyroid Diseases. National Institutes of Health (NIH).

Congenital Hypothyroidism. Genetics Home Reference (GHR).

Hypothyroidism. National Endocrine and Metabolic Diseases Information Service.