From the Guidelines
Hypothyroidism is primarily caused by Hashimoto's thyroiditis, which accounts for approximately 60-70% of all cases, followed by iatrogenic hypothyroidism, iodine deficiency, congenital hypothyroidism, and other less common causes. The causes of hypothyroidism can be broken down into the following percentages:
- Hashimoto's thyroiditis: 60-70% of cases, as an autoimmune condition where the body's immune system attacks the thyroid gland, gradually destroying its ability to produce thyroid hormones 1.
- Iatrogenic hypothyroidism: 20-25% of cases, resulting from medical treatments such as thyroid surgery or radioactive iodine therapy.
- Iodine deficiency: 5-10% of hypothyroidism cases globally, though this percentage is higher in regions with inadequate iodine in the diet.
- Congenital hypothyroidism: approximately 1 in 2,000-4,000 newborns, representing about 1% of all hypothyroidism cases.
- Other less common causes: certain medications (like lithium and amiodarone), pituitary or hypothalamic disorders (central hypothyroidism), and rare genetic disorders affecting thyroid hormone production or action, which make up less than 1% of cases. These percentages can vary somewhat based on geographic location, with iodine deficiency being more prevalent in developing countries and autoimmune thyroiditis more common in iodine-sufficient regions. The most common cause of hypothyroidism in the United States is chronic autoimmune (Hashimoto) thyroiditis, with risk factors for an elevated TSH level including female sex, advancing age, white race, type 1 diabetes, Down syndrome, family history of thyroid disease, goiter, previous hyperthyroidism, and external-beam radiation in the head and neck area 1.
From the Research
Primary Causes of Hypothyroidism
The primary causes of hypothyroidism can be broken down into several categories, including:
- Autoimmune thyroiditis (Hashimoto's thyroiditis)
- Drugs (such as amiodarone, lithium, and immune checkpoint inhibitors)
- Radioactive-iodine treatment
- Thyroid surgery
- Severe iodine deficiency
Percentage of Causes
According to the studies, the approximate percentage of causes of hypothyroidism are:
- Autoimmune cause accounts for approximately 90% of adult hypothyroidism, mostly due to Hashimoto's disease 2
- Other causes, including drugs, radioactive-iodine treatment, and thyroid surgery, are frequent but the exact percentage is not specified 3
- Severe iodine deficiency was the most common cause historically, but the current percentage is not specified 3
Sub-Causes of Autoimmune Thyroiditis
Autoimmune thyroiditis can be further broken down into sub-causes, including:
- Antibody dependent cytotoxicity
- K and NK cell cytotoxicity
- T lymphocyte cytotoxicity
- Lymphokine cytotoxicity
- Thyroid stimulation blocking antibody (TSBAb) 2