From the Guidelines
Hypothyroidism is most commonly caused by chronic autoimmune (Hashimoto) thyroiditis, with other significant causes including previous hyperthyroidism, external-beam radiation in the head and neck area, and certain risk factors such as female sex, advancing age, and family history of thyroid disease. The causes of hypothyroidism can be broken down into several key categories, including:
- Autoimmune disorders, such as Hashimoto thyroiditis, which is the most common cause of hypothyroidism in the United States 1
- Previous hyperthyroidism, possibly due to ablation therapy leading to iatrogenic thyroid dysfunction 1
- External-beam radiation in the head and neck area 1
- Risk factors such as female sex, advancing age, white race, type 1 diabetes, Down syndrome, family history of thyroid disease, goiter, and previous hyperthyroidism 1 It is essential to note that the USPSTF found no direct evidence that treatment of thyroid dysfunction based on risk level alters final health outcomes 1. The primary screening test for thyroid dysfunction is the serum TSH test, with multiple tests done over a 3- to 6-month interval to confirm or rule out abnormal findings 1. Treatment for hypothyroidism typically involves oral T4 monotherapy (levothyroxine sodium) 1.
From the FDA Drug Label
Amiodarone can cause either hypothyroidism or hyperthyroidism. Because of its release of inorganic iodine, or perhaps for other reasons, amiodarone can cause hypothyroidism. Hypothyroidism has been reported in 2 to 4% of patients in most series, but in 8 to 10% in some series
The causes of hypothyroidism include:
- The release of inorganic iodine from amiodarone
- Other unknown reasons related to amiodarone therapy 2
From the Research
Causes of Hypothyroidism
The causes of hypothyroidism can be varied and include:
- Autoimmune diseases, such as chronic autoimmune thyroiditis (Hashimoto's thyroiditis) 3, 4
- Radiation therapy 5, 3
- Thyroid gland removal surgeries 5, 3
- Certain medications, such as amiodarone, lithium, and immune checkpoint inhibitors 3
- Iodine deficiency or excess 6
- Consumptive hypothyroidism from excessive inactivation of thyroid hormone 7
- Central deficiency of thyrotropin-releasing hormone or thyroid-stimulating hormone (TSH) 7
Autoimmune Diseases
Autoimmune diseases, particularly Hashimoto's thyroiditis, are considered the most frequent cause of thyroid gland disorders 4. Infiltration of the thyroid gland with cytotoxic T-cells can lead to an initial thyrotoxicosis and during the course to hypothyroidism due to destruction of the thyroid gland 4.
Iodine Intake
There is evidence to suggest that elevated levels of iodide in the diet are associated with autoimmune thyroid disease (ATD) in susceptible individuals, and that autoimmune thyroiditis (Hashimoto's disease) is less common in susceptible individuals who live in regions with dietary iodine deficiency 6.