Major causes of hypothyroidism

Primary hypothyroidism

Chronic autoimmune thyroiditis

Iatrogenic

Thyroidectomy

Radioiodine therapy or external irradiation

Iodine deficiency or excess

Drugs - thionamides, lithium, amiodarone, interferon alfa, interleukin-2, tyrosine kinase inhibitors, checkpoint inhibitor immunotherapy

Infiltrative diseases - fibrous thyroiditis, hemochromatosis, sarcoidosis

Transient hypothyroidism

Painless (silent, lymphocytic) thyroiditis

Subacute granulomatous thyroiditis

Postpartum thyroiditis

Subtotal thyroidectomy

Following radioiodine therapy for Graves' hyperthyroidism

Following withdrawal of suppressive doses of thyroid hormone in euthyroid patients

Congenital thyroid agenesis, dysgenesis, or defects in hormone synthesis

Central hypothyroidism

TSH deficiency

TRH deficiency

Generalized thyroid hormone resistance (some patients)*

TRH: thyrotropin-releasing hormone; TSH: thyroid-stimulating hormone.
* Refer to UpToDate content on clinical features of thyroid hormone resistance.

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