Hypothyroidism is characterized by low thyroid activity in which fewer T3 and T4 hormones are produced. It is one of the most common endocrine conditions and is associated with symptoms like fatigue, weakness, low mood, dry skin, hair loss and weight gain.

The cause of hypothyroidism can be autoimmune in nature, or it can occur due to iodine deficiency. It can also develop due to abnormal functioning of the pituitary gland in the brain, as this gland produces TSH hormone, which stimulates the thyroid to produce T3 and T4.

Treatment for hypothyroidism is aimed at regulating thyroid hormone levels and thus relieving the symptoms. For this, endocrinologists usually prescribe synthetic hormones such as levothyroxine.

Signs and symptoms

Signs and symptoms associated with an underactive thyroid can appear gradually through the years. The lower the T3 and T4 hormone levels, the more prevalent the symptoms will be. The major signs and symptoms of hypothyroidism include:

Headache, muscle, and joint pain;
Irregular menstruation, which can cause trouble conceiving;
Fragile, breakable nails and dry, rough skin;
Swollen eyelids;
Hair loss and finer, dry, dull hair;
Slower heartbeat;
Constant fatigue;
Difficulty concentrating, and memory problems;
Low sex drive;
Increase in weight with no apparent cause.

In addition, there are cases where the person may undergo personality changes, depression, and dementia, however, these symptoms only happen with severely low levels of T3 and T4.

Hypothyroidism in children can also interfere with development. When experienced during adolescence, puberty may come later and the child may not grow as much. In addition, if a baby has congenital hypothyroidism, and it is not detected in the first week after birth, the child may show signs of neurological problems.

Complete our online symptom checker if you think you may have symptoms of a thyroid issue to assess your risk.

Confirming a diagnosis

To diagnose hypothyroidism, your family doctor or endocrinologist will start by evaluating your presenting symptoms, as well as your health history and family history. The doctor may also physically palpate your thyroid to assess for any nodules or physical changes.

To confirm a diagnosis, the doctor will then order blood tests and possibly imaging tests.

Tests for hypothyroidism

The main tests that are ordered to diagnose hypothyroidism are:

Thyroid hormones, such as T3 and T4, which are normally decreased
TSH levels, which is normally increased. Read more about the TSH blood test.
Thyroid ultrasound, when nodules are noted during palpation of the thyroid

In addition, the doctor may order blood test that check antithyroid antibodies, such as anti-thyroperoxidase (anti-TPO), and anti-thyroglobulin.

Types of hypothyroidism

The main types of hypothyroidism are:

1. Primary hypothyroidism

Primary hypothyroidism occurs when the thyroid gland itself is unable to produce adequate amounts of T3 and T4 hormones.

This type of hypothyroidism is usually related to Hashimoto's disease, which is an autoimmune thyroid condition.

2. Secondary hypothyroidism

Secondary hypothyroidism occurs when the thyroid gland functions normally, but the pituitary gland does not produce sufficient TSH.

The hormone TRH (thyrotropin-releasing hormone) stimulates the pituitary gland to produce TSH (thyroid-stimulating hormone), which stimulates the thyroid gland to produce T3 and T4.

3. Tertiary hypothyroidism

Tertiary hypothyroidism occurs due to a deficiency in the production of TRH in the hypothalamus, which affects the production of TSH in the pituitary gland.

It is not always possible to distinguish secondary from tertiary hypothyroidism, and therefore the doctor may opt to use a general hypothyroidism diagnosis to describe abnormal pituitary and hypothalamus functioning.

4. Subclinical hypothyroidism

Subclinical hypothyroidism is characterized by normal T4 levels and increased TSH levels. These person usually presents few or no symptoms of hypothyroidism.

Even when there are no symptoms noted, the doctor may prescribe medications, as these can help reduce the risk of cardiovascular problems. This is especially important for patients who already have high cholesterol and heart problems.

5. Congenital hypothyroidism

Congenital hypothyroidism occurs when the thyroid gland is unable to produce enough thyroid hormones, like T3 and T4, due to a defect noted at birth.

If this type of hypothyroidism is not detected within the first week after birth, the child may have neurological changes, and be at risk for a development delay.

6. Hypothyroidism in pregnancy

Hypothyroidism in pregnancy is usually the result of autoimmune changes, called Hashimoto's disease, in which the immune system itself produces antibodies that attack and destroy thyroid cells as if they were foreign to the body.

This type of hypothyroidism should be treated to prevent problems for the woman and the baby.

Hypothyroidism can also occur postpartum, a few months after the birth of the baby. Although this is usually temporary, also requires careful monitoring and treatment.

Possible causes

The main causes of hypothyroidism are:

Iodine deficiency
Hashimoto's thyroiditis
Radioactive iodine therapy on the thyroid
Radiation therapy to the head or neck area, or to the brain
Thyroid surgery
Tumor in the pituitary gland or hypothalamus

Furthermore, the use of medications such as lithium, amiodarone, thalidomide, phenytoin, phenobarbital, carbamazepine, interferon or imatinib, can increase the risk for hypothyroidism.

It is important to consult an endocrinologist so that the cause of hypothyroidism can be identified and treatment can be initiated.

Treatment options

Treatment for hypothyroidism should be carried out as guided by an endocrinologist, who may advise or prescribe:

1. Medications

Medications, like levothyroxine, may be prescribed by the endocrinologist to replace the hormones that are normally produced by the thyroid gland. Taking the right dose can stabilize thyroid levels and maintain them at normal levels.

The dose of the medication may vary throughout the treatment, and is adjusted according to hormone levels in the blood test.

2. Change in eating habits

Patients with hypothyroidism are often advised to opt for high-fiber foods with antioxidants and healthy fats, like Brazil nuts, oranges and eggs. Learn more about the hypothyroidism diet your doctor may recommend.

Signs of improvement or worsening

Signs of improvement in hypothyroidism appear approximately 2 weeks after starting treatment. Patients will typically notice a decrease in tiredness and an improvement in mood. Long-term treatment of hypothyroidism may also lead to better weight management and reduced blood cholesterol levels.

When the levothyroxine dose is not sufficient and thyroid levels are still not within normal limits, hypothyroidism symptoms may not improve. Very high doses of this medication, however, can lead to insomnia, nervousness, palpitations and tremors.

Possible complications

When hypothyroidism is severe and left untreated, it can lead to myxedema (which is very severe fluid retention), encephalopathy, decreased body temperature, seizures, hyponatremia, hypoglycemia, arrhythmias, cardiogenic shock or respiratory failure.

Myxedema treatment is carried out in the hospital setting, as it is a medical emergency and can be life-threatening.