Hypothyroidism: when thyroid doesn't make enough hormones

Hypothyroidism is an endocrine system disorder characterized by the inefficient action of thyroid hormones in the body, primarily due to insufficient production in the thyroid gland (primary hypothyroidism). It can also occur due to insufficient stimulation of the thyroid gland by TSH (thyroid-stimulating hormone) caused by a disorder affecting TSH production in the hypothalamic-pituitary system (secondary hypothyroidism).

In areas where iodine intake is sufficient, chronic autoimmune thyroiditis (Hashimoto's thyroiditis) is the most common cause of hypothyroidism. Globally, iodine deficiency remains the leading cause.

Hashimoto’s thyroiditis is an autoimmune disease characterized by the production of antibodies against thyroid peroxidase (anti-TPO) and thyroglobulin (anti-TG). This leads to the progressive destruction of the thyroid gland and, consequently, its function becomes increasingly impaired. Thus, Hashimoto’s thyroiditis is one of the primary causes of primary hypothyroidism.

The symptoms of hypothyroidism are often nonspecific. However, they typically include:

• Hard stools or constipation
• Sensitivity to cold (e.g., wearing a sweater when others are in a T-shirt)
• Fatigue or sluggishness
• Heavy or irregular menstrual periods
• Muscle or joint pain
• Dry or pale skin
• Sadness or depression
• Brittle or weak hair and nails
• Weakness
• Weight gain

If left untreated, additional late-stage symptoms may develop, including:

• Reduced sense of taste and smell
• Hoarseness
• Swelling of the face, hands, and feet
• Slow speech
• Thickened skin
• Thinning of the eyebrows
• Low body temperature
• Slow heart rate

Hypothyroidism is more common in women and individuals over the age of 50.

The most frequent cause of hypothyroidism is thyroiditis (inflammation of the thyroid gland, as seen in Hashimoto's thyroiditis). In people with thyroiditis, swelling and inflammation damage thyroid cells. However, other risk factors include:

• Viral infections (e.g., common cold) or other respiratory infections
• Pregnancy (often referred to as postpartum thyroiditis)
• Certain medications, such as lithium or amiodarone, and some types of chemotherapy
• Congenital abnormalities (present at birth)
• Radiation therapy to the neck or brain to treat various cancers
• Radioactive iodine used to treat an overactive thyroid
• Surgical removal of part or all of the thyroid gland
• Sheehan’s syndrome, a condition caused by heavy bleeding during pregnancy or childbirth that damages the pituitary gland (which regulates the thyroid gland)
• Pituitary tumor or pituitary gland surgery

The healthcare provider will conduct a physical examination and may find an enlarged thyroid gland. Typically, serum TSH and free thyroxine (free T4) levels are sufficient to diagnose primary or secondary hypothyroidism. In primary hypothyroidism, TSH levels are typically elevated, while free T4 levels are reduced. In contrast, both hormones are often reduced in secondary hypothyroidism.

Sometimes the thyroid gland is of normal size or smaller than normal. The examination may also reveal:

• High diastolic blood pressure (second number)
• Thin, brittle hair
• Coarse facial features
• Pale or dry skin, which may feel cold to the touch
• Reflexes with a delayed relaxation phase
• Swelling in the arms and legs

Blood tests to measure thyroid hormones TSH and T4 are usually ordered. Specialized thyroid tests, such as anti-TPO or anti-TG antibodies, may also be required.

Other tests may check for:

• Cholesterol levels
• Complete blood count (CBC)
• Liver enzymes
• Prolactin
• Sodium
• Cortisol

The goal of treatment is to replace the missing thyroid hormone. Levothyroxine is the most commonly used medication. After starting treatment, the provider may check hormone levels every 2-3 months. Subsequently, thyroid hormone levels should be monitored at least annually.

There is no known way to completely prevent hypothyroidism. However, controlling iodine levels in the diet and adjusting them to the recommended amount is the only preventive measure available. This is because iodine plays a crucial role in thyroid gland function, being an essential element for the conversion of thyroglobulin into the two types of thyroid hormones: triiodothyronine (T3) and thyroxine (T4). Thus, iodine deficiency disrupts thyroid function and, if left untreated, can lead to hypothyroidism.