Types of Hypothyroidism


What is hypothyroidism?

Hypothyroidism, or underactive thyroid disease, is a common condition that occurs when the thyroid gland does not produce adequate amounts of the thyroid stimulating hormone. Located in the lower front portion of the neck, the thyroid gland releases a crucial hormone that travels through the bloodstream. Thyroid hormones are essential in controlling how cells use energy. Hypothyroidism can impact the body’s general functionality.

Types of hypothyroidism

There are three types of hypothyroidism, which include primary, secondary and tertiary. The majority of hypothyroidism cases are diagnosed as primary hypothyroidism.

Primary hypothyroidism

The thyroid is the root cause of primary hypothyroidism. It may receive proper stimulation, but the amount of thyroid hormone produced (if any) is inadequate for the body’s functionality. The most common cause of primary hypothyroidism is Hashimoto’s thyroiditis, an autoimmune disease during which the body’s immune system mistakenly attacks the thyroid. Other causes may include the following:

  • Hyperthyroidism treatment that destroys the thyroid
  • Partial or total removal of the thyroid
  • Certain medications
  • Congenital disease
  • Iodine deficiency
  • Viral thyroiditis
  • Hormonal changes after giving birth

Treatment for primary hypothyroidism includes hormone replacement medication, which is necessary for the maintenance of hypothyroidism. Stopping medication allows symptoms to return.

Secondary hypothyroidism

The pituitary gland produces thyroid-stimulating hormones (TSH). TSH stimulates the thyroid to produce thyroid hormones. When the pituitary gland stops working properly, the production of TSH decreases or halts, which impacts the thyroid’s production of hormones. This results in secondary hypothyroidism. The thyroid gland works properly otherwise in this type of hypothyroidism. Hypopituitarism can be caused by the following:

  • Brain infection or inflammation
  • Head trauma
  • Tumors in the pituitary gland or hypothalamus
  • Stroke
  • Brain tumor
  • Brain surgery
  • Pituitary apoplexy (tissue death in the pituitary gland)
  • Subarachnoid hemorrhage (resulting from burst aneurysm)
  • Radiation therapy to the brain
  • Lymphocytic hypophysitis (autoimmune disorder)
  • Excessive iron
  • Abnormal increase of histiocytosis (immune cells)
  • Infections of the pituitary gland
  • Inflammation of various tissues and organs (sarcoidosis)
  • Sheehan syndrome (blood loss during pregnancy)
  • Certain medications, such as glucocorticoids or medications to treat cancer

Tertiary hypothyroidism

Tertiary hypothyroidism indicates a problem with a source separate from the thyroid. When the hypothalamus does not produce enough thyroid-releasing hormone (TRH), the pituitary gland releases inadequate amounts of TSH (thyroid-stimulating hormone). The lack of TSH will then result in an otherwise properly working thyroid gland being unable to produce enough thyroid hormone. Tumors and other diseases associated with the hypothalamus can also cause a decreased production of TRH, resulting in the presence of tertiary hypothyroidism.

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