Hypothyroidism is a condition that’s characterised by abnormally low thyroid hormone production. There are several disorders that can result in hypothyroidism, and these disorders may directly or indirectly involve the thyroid gland. As the thyroid hormone affects growth, development, and many cellular processes, inadequate thyroid hormone has widespread consequences for the body.
The easiest way to understand hypothyroidism is to consider its root meaning. ‘Hypo’ means too little, while ‘thyroidism’ is a disease of the thyroid. Hypothyroidism, therefore, is a disease of too little thyroid activity.
What Are Thyroid Hormones?
Thyroid hormones are produced by the thyroid gland. This gland is located in the lower part of the neck, below the Adam’s apple. The gland wraps around the windpipe (trachea) and has a shape that is similar to a butterfly, formed by two wings (lobes) and attached by a middle part (isthmus).
The thyroid gland uses iodine (mostly available from the diet in foods such as seafood, bread, and salt) to produce thyroid hormones. The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3), which account for 99% and 1% of thyroid hormones present in the blood respectively. However, the hormone with the most biological activity is T3. Once released from the thyroid gland into the blood, a large amount of T4 is converted into T3, the active hormone that affects the metabolism of cells.
What Causes Hypothyroidism?
Hypothyroidism is a very common condition. It is more common in women than in men, and its incidence increases with age. Here are some of the common causes of hypothyroidism in adults.
Inflammation of the Thyroid Gland (Thyroiditis)
Hypothyroidism often results from previous or currently ongoing inflammation of the thyroid gland, which leaves a large percentage of the cells of the thyroid damaged (or dead) and incapable of producing sufficient hormone. The most common cause of thyroid gland failure is called autoimmune thyroiditis (also called Hashimoto’s thyroiditis) or, in other words, thyroid inflammation caused by a person’s own immune system.
Hashimoto’s thyroiditis is an autoimmune disorder that’s caused by the immune system attacking healthy tissues. In Hashimoto’s disease, immune-system cells lead to the death of the thyroid’s hormone-producing cells.
This fairly broad category includes procedures or medications that affect the thyroid’s ability to produce enough hormones to meet the body’s demands. Some of these hypothyroidism-causing treatments are done to address another thyroid disorder, but can have the side effect of inducing hypothyroidism. For example, the treatment of many thyroid conditions – including thyroid cancer – requires surgical removal of a portion or all of the thyroid gland. If the thyroid-producing cells left in the body are not enough to meet the needs of the body, the patient will develop hypothyroidism.
What Are the Risk Factors for Hypothyroidism?
Anyone can develop hypothyroidism, but you are at increased risk if you:
- are a woman
- are over the age of 50
- were pregnant or had a baby within the past six months
- have a family history of thyroid disease or any autoimmune disorder
- have an autoimmune disorder, such as type 1 diabetes or rheumatoid arthritis
- have taken antithyroid medications (a treatment for hyperthyroidism) or have been treated with radioactive iodine
- have had thyroid surgery (partial or total thyroidectomy)
- have been exposed to radiation to your neck or upper chest area
What Are the Symptoms of Hypothyroidism?
The symptoms of hypothyroidism can vary with the severity of the deficiency in thyroid hormone production and the length of time that the body has been deprived of the proper amount of hormone. Symptoms also vary between individuals – what may be one person’s main complaint might not affect another person. Most people will have a combination of symptoms. Occasionally, some patients with hypothyroidism may have no symptoms at all, or they are so subtle that they go unnoticed. These symptoms are:
- Weight gain or increased difficulty losing weight
- Coarse, dry hair
- Dry, rough pale skin
- Hair loss
- Cold intolerance (you can’t tolerate cold temperatures like those around you)
- Muscle cramps and frequent muscle aches
- Memory loss
- Abnormal menstrual cycles
- Decreased libido
If you have one or more of the symptoms listed, contact your doctor. Additionally, you may need to seek the skills of an endocrinologist. If you have already been diagnosed and treated for hypothyroidism and continue to have any or all of these symptoms, it’s important to discuss it with your physician(s).
How Is Hypothyroidism Diagnosed?
A diagnosis of hypothyroidism can take into account the following:
Medical and Family History
You should take care to tell your doctor if any of the following points are a part of your medical and family history.
- Changes in your health that suggest that your body is slowing down
- If you’ve ever had thyroid surgery
- If you’ve ever had radiation to your neck to treat cancer
- If you’re taking any of the medicines that can cause hypothyroidism (such as amiodarone, lithium, interferon alpha, interleukin-2, and maybe thalidomide)
- Whether any of your family members have thyroid disease
The doctor will check your thyroid gland and look for changes such as dry skin, swelling, slower reflexes, and a slower heart rate.
Two blood tests are used in the diagnosis of hypothyroidism.
TSH (Thyroid-Stimulating Hormone) Test
This is the most important and sensitive test for hypothyroidism. It measures how much of the thyroid hormone thyroxine (T4) the thyroid gland is being asked to make. An abnormally high TSH means hypothyroidism – the thyroid gland is being asked to make more T4 because there isn’t enough T4 in the blood.
Most of the T4 in the blood is attached to a protein called thyroxine-binding globulin. The “bound” T4 can’t get into body cells. Only about 1% – 2% of T4 in the blood is unattached (“free”) and can get into cells. The free T4 and the free T4 index are both simple blood tests that measure how much unattached T4 is in the blood and available to get into cells.
How Is Hypothyroidism Treated?
Hypothyroidism can’t be cured, but in almost every patient, can be completely controlled. It is treated by replacing the amount of hormone that your own thyroid can no longer make in order to bring your T4 and TSH levels back to normal levels. So, even if your thyroid gland can’t work right, T4 replacement can restore your body’s thyroid hormone levels and your body’s function. Synthetic thyroxine pills contain a hormone exactly like the T4 that the thyroid gland itself makes. All hypothyroid patients except those with severe myxedema (life-threatening hypothyroidism) can be treated as outpatients, not having to be admitted to the hospital.
Are There Any Side Effects of Treatment?
The only dangers of thyroxine are caused by taking too little or too much. If you take too little, your hypothyroidism will continue. If you take too much, you’ll develop the symptoms of hyperthyroidism, an overactive thyroid gland.
The most common symptoms of too much thyroid hormone are fatigue, an inability to sleep, greater appetite, nervousness, shakiness, feeling hot when other people are cold, and trouble exercising because of weak muscles, shortness of breath, and a racing skipping heart. Patients who have hyperthyroid symptoms at any time during thyroxine replacement therapy should have their TSH tested. If it is low, indicating too much thyroid hormone, their dose needs to be lowered.