- Douglas S Ross, MD
Douglas S Ross, MD
- Section Editor — Thyroid Disease
- Professor of Medicine
- Harvard Medical School
Exogenous hyperthyroidism is the term used to describe hyperthyroidism caused by ingestion of excessive amounts of thyroid hormone. It may be intentional (ie, suppressive doses of thyroxine to treat thyroid cancer) or inadvertent (ie, contamination of dietary supplements). When exogenous hyperthyroidism is due to the surreptitious ingestion of thyroid hormone, it is termed thyrotoxicosis factitia.
The clinical manifestations, diagnosis, and treatment of exogenous hyperthyroidism will be reviewed here. An overview of disorders that cause hyperthyroidism is found elsewhere. (See "Disorders that cause hyperthyroidism".)
Exogenous hyperthyroidism is caused by the ingestion of excessive amounts of thyroid hormone. Levothyroxine (T4) is the most widely used thyroid hormone preparation, but the hormone is also available as liothyronine (T3, Cytomel), thyroid extract (desiccated thyroid), and mixtures of synthetic T4 and T3 (liotrix, Thyrolar). Symptoms from exogenous hyperthyroidism frequently occur at doses in excess of 200 mcg for T4, 50 mcg for T3, 120 mg for desiccated thyroid, and 37.5 mcg T3/150 mcg T4 for Thyrolar. However, most patients are taking considerably higher doses.
Exogenous hyperthyroidism can occur in several clinical settings . As examples:
●Patients with thyroid cancer prescribed suppressive doses of thyroxine to minimize potential thyroid-stimulating hormone (TSH) stimulation of tumor growth.
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