Etiology:
Hypothyroidism is primarily divided into primary and secondary (central) types. Primary hypothyroidism, where the thyroid gland fails to produce enough hormones, is most commonly caused by iodine deficiency in iodine-deficient areas and autoimmune thyroid diseases like Hashimoto thyroiditis in iodine-sufficient regions. Other causes include postpartum thyroiditis, radioactive iodine treatment for Graves' disease, subacute granulomatous thyroiditis (de Quervain disease), autoimmune polyendocrinopathy syndromes, certain medications, thyroid surgery, radiotherapy, and immune checkpoint inhibitors. Secondary hypothyroidism occurs due to dysfunction in the pituitary gland or hypothalamus, caused by various conditions such as tumors, Sheehan syndrome, TRH resistance or deficiency, lymphocytic hypophysitis, radiation therapy to the brain, and certain medications like dopamine, prednisone, or opioids.
(Patil, Rehman, Anastasopoulou, et al., 2024)