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Oral contraceptive use
Surreptitious use of levothyroxine
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The patient is presenting with elevated total thyroid hormone levels, but normal free T4 and T3 levels, likely caused by her newly initiated oral contraceptive pills. An increased estrogen state can cause an increase in thyroid-binding globulins (TBG). In effect, total thyroid hormone levels will increase, while free thyroxine (T4) and triiodothyronine (T3) levels remain normal. Some causes of hyperestrogenemia include hormonal contraception, hormone replacement therapy, and hormone-secreting ovarian tumors. These patients are clinically euthyroid and do not have issues with hyperthyroidism. Treatment is observation and reassurance. Torre et al. review the evidence regarding the effect of estrogen on thyroid hormone function. They discuss how estrogen can modulate the level of circulating thyroid hormones. They recommend screening for subclinical hypothyroidism.Incorrect Answers:Answer 1: Familial hyperthyroidism would result in low thyroid-stimulating hormone (TSH) levels, with an increase in both total and free T4 and T3 levels. Familial hyperthyroidism is caused by a mutation in a TSH receptor. It can present with mild to severe symptoms of hyperthyroidism (diarrhea, palpitations, weight loss, increased appetite, heat intolerance). Answer 2: Hypocholesterolemia can be caused by hyperthyroidism, but itself would not be the cause of an increase in thyroid hormone levels.Answer 3: Lithium causes an increase in iodine content within the thyroid which inhibits the release of T4 and T3. Lithium most commonly causes goiter or hypothyroidism. Lithium has also been less commonly associated with hyperthyroidism, though TSH would be low while both total and free thyroid hormone levels would be elevated.Answer 5: Surreptitious use of levothyroxine would cause a low serum TSH. Serum T4 and/or T3 may be elevated or normal. Treatment is with cessation of surreptitious thyroid hormone use. Bullet Summary: Any increased estrogen state can cause an elevation in TBG and total thyroid hormone levels, while free T4 and T3 levels remain normal.
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