Hypothyroidism: Overview, Causes, Symptoms, and Risk Factors

 

This week, we are discussing another common thyroid issue: Hypothyroidism. As you know, the thyroid is a small, butterfly-shaped gland situated at the base of the front of the neck, just below the Adam's apple. Hormones produced by the thyroid gland — triiodothyronine (T3) and thyroxine (T4) — have an enormous impact on health, affecting all aspects of metabolism. These hormones also influence the control of vital functions, such as body temperature and heart rate.

Hypothyroidism Defined

When our thyroid doesn't produce enough of certain crucial hormones, the balance of chemical reactions in our body can be upset. This is commonly referred to Hypothyroidism (underactive thyroid).

Accurate thyroid function tests are available to diagnose hypothyroidism. Treatment with synthetic thyroid hormone is usually simple, safe and effective once you and your doctor determine the appropriate dosage.

Causes

There can be many reasons why the cells in the thyroid gland can’t make enough thyroid hormone. Here are the major causes, from the most to the least common:

Autoimmune disease. In some people’s bodies, the immune system that protects the body from invading infections can mistake thyroid gland cells and their enzymes for invaders and can attack them. Then there aren’t enough thyroid cells and enzymes left to make enough thyroid hormone. This is more common in women than men. Autoimmune thyroiditis can begin suddenly or it can develop slowly over years. The most common forms are Hashimoto’s thyroiditis and atrophic thyroiditis.

Surgical removal of part or all of the thyroid gland. Some people with thyroid nodules, thyroid cancer, or Graves’ disease need to have part or all of their thyroid removed. If the whole thyroid is removed, people will definitely become hypothyroid. If part of the gland is left, it may be able to make enough thyroid hormone to keep blood levels normal.

Radiation treatment. Some people with Graves’ disease, nodular goiter, or thyroid cancer are treated with radioactive iodine (I-131) for the purpose of destroying their thyroid gland. Patients with Hodgkin’s disease, lymphoma, or cancers of the head or neck are treated with radiation. All these patients can lose part or all of their thyroid function.

Congenital hypothyroidism (hypothyroidism that a baby is born with). A few babies are born without a thyroid or with only a partly formed one. A few have part or all of their thyroid in the wrong place (ectopic thyroid). In some babies, the thyroid cells or their enzymes don’t work right.

Thyroiditis. Thyroiditis is an inflammation of the thyroid gland, usually caused by an autoimmune attack or by a viral infection. Thyroiditis can make the thyroid dump its whole supply of stored thyroid hormone into the blood at once, causing brief hyperthyroidism (too much thyroid activity); then the thyroid becomes underactive.

Medicines. Medicines such as amiodarone, lithium, interferon alpha, and interleukin-2 can prevent the thyroid gland from being able to make hormone normally. These drugs are most likely to trigger hypothyroidism in patients who have a genetic tendency to autoimmune thyroid disease.

Too much or too little iodine. The thyroid gland must have iodine to make thyroid hormone. Iodine comes into the body in food and travels through the blood to the thyroid. Keeping thyroid hormone production in balance requires the right amount of iodine. Taking in too much iodine can cause or worsen hypothyroidism.

Damage to the pituitary gland. The pituitary, or “master gland,” tells the thyroid how much hormone to make. When the pituitary is damaged by a tumor, radiation, or surgery, it may no longer be able to give the thyroid instructions, and the thyroid may stop making enough hormone.

Rare disorders that infiltrate the thyroid. In a few people, diseases deposit abnormal substances in the thyroid and impair its ability to function. For example, amyloidosis can deposit amyloid protein, sarcoidosis can deposit granulomas, and hemochromatosis can deposit iron.

Symptoms

The signs and symptoms of hypothyroidism vary, depending on the severity of the hormone deficiency. Hypothyroidism may not cause noticeable symptoms in the early stages, but over time, untreated hypothyroidism can cause a number of health problems, such as obesity, joint pain, infertility, and heart disease. At first, we may barely notice the symptoms of hypothyroidism, such as fatigue and weight gain. Often, we simply attribute these symptoms to getting older. But as our metabolism continues to slow, we may develop more-obvious problems. Hypothyroidism signs and symptoms may include:

  •  Fatigue

  •  Increased sensitivity to cold

  •  Constipation

  •  Dry skin

  •  Weight gain

  •  Puffy face

  •  Hoarseness

  •  Muscle weakness

  •  Elevated blood cholesterol level

  •  Muscle aches, tenderness, and stiffness

  •  Pain, stiffness or swelling in your joints

  •  Heavier than normal or irregular menstrual periods

  •  Thinning hair

  •  Slowed heart rate

  •  Depression

  •  Impaired memory

  •  Enlarged thyroid gland (goiter)

Risk factors

Although anyone can develop hypothyroidism, there is an increased risk if you:

  •  Are a woman

  •  Are older than 60

  •  Have a family history of thyroid disease

  •  Have an autoimmune disease, such as type 1 diabetes or celiac disease

  •  Have been treated with radioactive iodine or anti-thyroid medications

  •  Received radiation to your neck or upper chest

  •  Have had thyroid surgery (partial thyroidectomy)

  •  Have been pregnant or delivered a baby within the past six months

Complications

Untreated hypothyroidism can lead to a number of health problems, including:

Goiter. Constant stimulation of the thyroid to release more hormones may cause the gland to become larger — a condition known as a goiter. Although generally not uncomfortable, a large goiter can affect physical appearance and may interfere with swallowing or breathing.

Heart problems. Hypothyroidism may also be associated with an increased risk of heart disease and heart failure, primarily because high levels of low-density lipoprotein (LDL) cholesterol — the "bad" cholesterol — can occur in people with an underactive thyroid.

Mental health issues. Depression may occur early in hypothyroidism and may become more severe over time. Hypothyroidism can also cause slowed mental functioning.

Peripheral neuropathy. Long-term uncontrolled hypothyroidism can cause damage to peripheral nerves. These are the nerves that carry information from our brain and spinal cord to the rest of our body — for example, our arms and legs. Peripheral neuropathy may cause pain, numbness and tingling in affected areas.

Myxedema. This rare, life-threatening condition is the result of long-term, undiagnosed hypothyroidism. Its signs and symptoms include intense cold intolerance and drowsiness followed by profound lethargy and unconsciousness. A myxedema coma may be triggered by sedatives, infection or other stress on your body. If you have signs or symptoms of myxedema, you need immediate emergency medical treatment.

Infertility. Low levels of thyroid hormone can interfere with ovulation, which impairs fertility. In addition, some of the causes of hypothyroidism — such as autoimmune disorder — can also impair fertility.

Birth defects. Babies born to women with untreated thyroid disease may have a higher risk of birth defects compared to babies born to healthy mothers. These children are also more prone to serious intellectual and developmental problems. Infants with untreated hypothyroidism present at birth are at risk of serious problems with both physical and mental development. But if this condition is diagnosed within the first few months of life, the chances of normal development are excellent.

As we wrap up National Thyroid Awareness Month next week, we will discuss the various methods used to diagnose thyroid disorders and treatment options available for each.