Do you have hypothyroidism and how does it occur?

Hypothyroidism: Where does it come from?

As with many diseases and disorders, not all causes of hypothyroidism stem from one particular source. Most cases of hypothyroidism (the underactive thyroid) are caused by problems that start in the thyroid gland.

These cases are known as primary hypothyroidism. Secondary hypothyroidism is caused by problems attacking the pituitary gland, while tertiary hypothyroidism develops due to problems arising in the hypothalamus. To understand the causes of hypothyroidism, the first step is to break it down into three types of hypothyroidism: primary, secondary, and tertiary.

Hashimoto’s thyroiditis is the most common cause of primary hypothyroidism. Hashimoto’s is an autoimmune disease in which the body’s immune system begins to attack the thyroid, preventing it from producing the proper amount of hormones. To combat this disease, the thyroid tries to work even harder, often leading to an enlarged thyroid gland, medically known as a goiter.

Another less common cause of hypothyroidism is a negative reaction to radioactive ablation therapy. This type of therapy is commonly given to patients who have been diagnosed with hyperthyroidism or who have recently received surgical treatment for thyroid cancer. It is estimated that 80-90% of patients undergoing this therapy will develop hypothyroidism within 2-3 months.

Other thyroid disorders that result from primary hypothyroidism include subacute, silent, and postpartum thyroiditis.

• Subacute thyroiditis: caused by a viral infection that causes the immune system to release a large number of lymphocytes (blood cells that determine the immune response against a virus). These lymphocytes attack the thyroid tissue and cause temporary or permanent hypothyroidism.
• Silent thyroiditis: Caused by an autoimmune disorder that causes the immune system to release lymphocytes that invade the follicles of the thyroid gland. In this case, the thyroid is also under attack, leading to temporary or permanent underactivity and hypothyroidism.
• Postpartum thyroiditis: 6-8% of women develop symptoms of hyperthyroidism followed by hypothyroidism 6 weeks to 6 months after delivery. In many cases, the thyroid returns to normal after a year, but other cases result in permanent hypothyroidism.

In rare cases, primary hypothyroidism can result from neck exposure to radiation, certain medications that affect thyroid hormone production, or iodine deficiency. Since the thyroid depends on iodine to function properly, a deficiency of this mineral can lead to thyroid problems. Due to the fact that most foods in the US are fortified with iodine, this deficiency is almost exclusive to underdeveloped countries.

Secondary hypothyroidism is less common, but is usually caused by damage to the pituitary gland from radiation, surgery, or a tumor.

• Hypopituitarism is the decreased secretion of one or more of the hormones produced by the pituitary gland, while panhypopituitarism is the complete depletion of all hormone production by the pituitary gland. Since this gland tells the thyroid what to do, a change in the pituitary’s hormone production also affects the thyroid’s hormone production.
• Sheehan syndrome usually develops after pregnancy due to low blood pressure. This syndrome causes postpartum hypopituitarism, which can lead to temporary or permanent secondary hypothyroidism.
• The development of pituitary tumors can also affect the production of pituitary hormones, which in turn leads to malfunction of the thyroid gland, resulting in hypothyroidism.

The third and least common type of hypothyroidism is tertiary hypothyroidism, which is usually caused by dysfunction of the hypothalamus. This part of the brain is in charge of telling the pituitary gland what to do and how many hormones to produce. When this part of the brain is negatively affected by a disorder, the pituitary gland and the thyroid gland are also affected.

While each of these three types of thyroid disorders are caused by different factors, the symptoms of thyroid problems remain the same regardless of which subtype of hypothyroidism you have.

However, thyroid disorder symptoms differ between hypothyroidism and hyperthyroidism (overactive thyroid), so it’s important to understand the differences between the two when determining which type of thyroid disorder you have.

Understanding the causes of hypothyroidism is one of the first steps to better understanding your body and getting better treatment; the more you know, the better educated you will be when making treatment decisions.