Info
exogenous thyroid hormone
SUMMARY AND RECOMMENDATIONS
Causes
- Exogenous hyperthyroidism is the term used to describe hyperthyroidism caused by ingestion of excessive amounts of thyroid hormone.
- It may be intentional or inadvertent.
- ingestion of excessive doses to treat thyroid cancer or to shrink the thyroid gland in patients with goiter, or through ingestion of weight-reducing dietary supplements containing levothyroxine (T4), liothyronine (T3), or animal thyroid tissue.
Clinical features
- The symptoms and signs in patients who take excessive doses of thyroid hormone are like those in patients with hyperthyroidism from other causes and include weight loss, heat intolerance, tremor, palpitations, anxiety, increased frequency of bowel movements, and shortness of breath. Unless underlying thyroid disease is present, there is no goiter or ophthalmopathy. (See ‘Clinical features’ above and “Overview of the clinical manifestations of hyperthyroidism in adults”.)
Diagnosis
- The diagnosis of exogenous hyperthyroidism is based upon clinical manifestations (presence of hyperthyroid symptoms, absence of goiter), abnormal thyroid function tests (low TSH, elevated or normal free thyroxine [T4] and/or triiodothyronine [T3]), a low serum thyroglobulin (Tg) concentration, and
- Gold: a low or undetectable 24-hour radioiodine uptake. (See ‘Diagnosis’ above.)
Treatment
- Discontinuation or reduction in the dose of thyroid hormone is treatment needed for most patients.
- When therapy is stopped in patients taking thyroxine, serum T4 concentrations fall approximately 50 percent in seven days.
- T3 is cleared more fast (serum half-life one day). (See ‘Treatment’ above.)
Beta-adrenergic antagonist drugs
can be used briefly to immediately relieve many of the symptoms of hyperthyroidism. (See “Beta blockers in the treatment of hyperthyroidism”.)