A 31-year-old woman, gravida 1 para 1, comes to the office 5 weeks after an uneventful vaginal delivery. She has fatigue, sweating, and heat intolerance. The patient has lost a significant amount of weight, which she believes is expected following delivery. She has had no skin rash, headache, vision changes, or ocular symptoms, and her appetite is normal. The patient is not breastfeeding and states that she "dried out quickly." She has not yet resumed her normal menstruation. The patient's medical history is unremarkable, and her only medication is a daily prenatal vitamin that she continued following her delivery "to maintain her vitamin balance." She quit smoking 10 years ago after smoking for 2 years in college, and she does not drink alcohol or use recreational drugs. The patient's mother has hypothyroidism and celiac disease. Blood pressure is 121/67 mm Hg and pulse is 109/min. Examination shows an enlarged, nontender thyroid gland with no nodules. Ocular examination shows mild lid lag without proptosis. The remainder of the examination is unremarkable. Laboratory results are as follows: The radioactive iodine uptake in the thyroid gland is 1.5% at 24 hours (normal: 8%-25%). Which of the following is the most likely diagnosis?

Question

A 31-year-old woman, gravida 1 para 1, comes to the office 5 weeks after an uneventful vaginal delivery.  She has fatigue, sweating, and heat intolerance.  The patient has lost a significant amount of weight, which she believes is expected following delivery.  She has had no skin rash, headache, vision changes, or ocular symptoms, and her appetite is normal.  The patient is not breastfeeding and states that she "dried out quickly."  She has not yet resumed her normal menstruation.  The patient's medical history is unremarkable, and her only medication is a daily prenatal vitamin that she continued following her delivery "to maintain her vitamin balance."  She quit smoking 10 years ago after smoking for 2 years in college, and she does not drink alcohol or use recreational drugs.  The patient's mother has hypothyroidism and celiac disease.  Blood pressure is 121/67 mm Hg and pulse is 109/min.  Examination shows an enlarged, nontender thyroid gland with no nodules.  Ocular examination shows mild lid lag without proptosis.  The remainder of the examination is unremarkable.  Laboratory results are as follows:  The radioactive iodine uptake in the thyroid gland is 1.5% at 24 hours (normal: 8%-25%).  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

Explanation: This patient has primary hyperthyroidism (elevated T4, suppressed TSH). In light of her nontender goiter and recent pregnancy, this is consistent with postpartum thyroiditis (PT). PT (by definition occurring <1 year following pregnancy) is similar to silent thyroiditis; both are associated with thyroid peroxidase antibody and are considered variants of chronic lymphocytic (Hashimoto) thyroiditis. Both PT and silent thyroiditis typically have a transient hypothyroid phase before returning to a normal euthyroid state, whereas most patients with classic Hashimoto thyroiditis have residual hypothyroidism. A radioactive iodine uptake (RAIU) test can distinguish Graves disease, which causes increased thyroid hormone synthesis, from PT and silent thyroiditis, which are characterized by thyroid inflammation and release of preformed hormone. Graves disease has a high RAIU, whereas PT and silent thyroiditis have a low RAIU (Choice A). Thyroglobulin is co-secreted with thyroid hormone by thyroid follicles and is low in patients with exogenous thyrotoxicosis (due to suppression of follicular activity by exogenous thyroid hormone), but is elevated in PT (due to destruction of thyroid follicles) and Graves disease (due to increased activity of follicles). (Choice B) Increased estrogen production during pregnancy leads to increased levels of thyroxine-binding globulin. Concurrently, hCG (which shares structural homology with TSH) causes increased release of thyroxine from the thyroid. Pregnant women typically have elevated total T4 levels but metabolically normal thyroid function (euthyroid hyperthyroxinemia). However, thyroxine-binding globulin and T4 normalize rapidly following delivery, and the undetectable TSH in this patient is more consistent with PT. (Choice D) Postpartum pituitary necrosis (Sheehan syndrome) is seen following severe obstetric hemorrhage and hypotension. Failure of lactation is a common presenting symptom, but patients have central hypothyroidism rather than primary hyperthyroidism. (Choice E) Subacute granulomatous (de Quervain) thyroiditis can cause transient hyperthyroidism due to follicular injury and release of preformed hormone. Patients have a low TSH, elevated T4, elevated thyroglobulin, and low RAIU. However, patients usually also have a tender thyroid gland and a history of recent viral infection. Educational objective: Postpartum thyroiditis (PT) presents with hyperthyroidism and a nontender goiter in the first year after pregnancy. It is similar to silent thyroiditis; both are associated with thyroid peroxidase antibodies and are considered variants of chronic lymphocytic (Hashimoto) thyroiditis. Both PT and silent thyroiditis typically have a transient hypothyroid phase before returning to a normal euthyroid state. References: Postpartum thyroiditis. (http://www.ncbi.nlm.nih.gov/pubmed/25434070) Approach to the patient with postpartum thyroiditis. (http://www.ncbi.nlm.nih.gov/pubmed/22312089)

A 31-Year-Old Woman, Gravida 1 Para 1, Comes to the Office