Review Question - QID 210086

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Estrogens Introduction Toxicity QID: 210086 (M2.OMB.18.1)

QID 210086 (Type "210086" in App Search)

An 18-year-old girl comes to the clinic because she is concerned about her weight. She is on her school’s cheerleading team and is upset because she feels she is the “fattest” girl on the team despite her healthy diet. In the last 2 weeks since practice began, she has lost 2 lbs. The patient has bipolar disorder. Her medications include lithium and a combined oral contraceptive pills that were recently started by her gynecologist, because “everyone is on it." Her mother has hypothyroidism and is treated with levothyroxine. Her temperature is 98.6°F (37.0°C), blood pressure is 117/78 mmHg, pulse is 90/min, respirations are 14/min, and oxygen saturation is 98% on room air. The patient’s BMI is 23.2 kg/m2. Thyroid function labs are drawn and shown below: Thyroid-stimulating hormone (TSH): 4.0 mIU/L Serum thyroxine (T4): 18 ug/dL Free thyroxine (Free T4): 1.4 ng/dl (normal range: 0.7-1.9 ng/dL) Serum triiodothyronine (T3): 210 ng/dL Free triiodothyronine (T3): 6.0 pg/mL (normal range: 3.0-7.0 pg/mL) Which of the following is the most likely cause of the patient’s abnormal lab values?

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Familial hyperthyroidism

1/45

Hypocholesterolemia

0/45

Lithium

20%

9/45

Oral contraceptive use

49%

22/45

Surreptitious use of levothyroxine

22%

10/45

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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.