A 64-year-old man comes to the hospital due to fever, diarrhea, hematochezia, and abdominal pain for the past 4-5 days. He has had 10 bloody stools a day. The patient has a history of ulcerative colitis and discontinued treatment a few months ago because he had not had a flare of symptoms for 2 years. He has no other medical problems. Temperature is 37.3 C (99.1 F), blood pressure is 100/74 mm Hg, pulse is 110/min, and respirations are 16/min. Physical examination shows tenderness in the left lower quadrant without rebound or guarding. Digital rectal examination shows gross blood. The patient is started on intravenous fluids, oral glucocorticoids, oral 5-aminosalicylic acid, and glucocorticoid enemas. On the second hospital day, serum sodium is 133 mEq/L, potassium is 3.6 mEq/L, and serum creatinine is 1.4 mg/dL. Thyroid function tests are as follows: Which of the following is the primary reason for the thyroid test results in this patient?

Question

A 64-year-old man comes to the hospital due to fever, diarrhea, hematochezia, and abdominal pain for the past 4-5 days.  He has had >10 bloody stools a day.  The patient has a history of ulcerative colitis and discontinued treatment a few months ago because he had not had a flare of symptoms for 2 years.  He has no other medical problems.  Temperature is 37.3 C (99.1 F), blood pressure is 100/74 mm Hg, pulse is 110/min, and respirations are 16/min.  Physical examination shows tenderness in the left lower quadrant without rebound or guarding.  Digital rectal examination shows gross blood.  The patient is started on intravenous fluids, oral glucocorticoids, oral 5-aminosalicylic acid, and glucocorticoid enemas.  On the second hospital day, serum sodium is 133 mEq/L, potassium is 3.6 mEq/L, and serum creatinine is 1.4 mg/dL.  Thyroid function tests are as follows:  Which of the following is the primary reason for the thyroid test results in this patient?

Quizplus · Accepted Answer

11ec25c8_d3c4_f5a6_bc81_41fe10d50b1c_MD0003_00 This patient with low serum (total) T3, normal serum (total) T4, and normal TSH in the setting of acute illness (eg, ulcerative colitis flare treated with glucocorticoids) has euthyroid sick syndrome (ESS). T4 is produced exclusively in the thyroid gland, whereas T3 is produced mainly by peripheral conversion of T4 by deiodination. ESS encompasses a variety of alterations in thyroid physiology, the most common of which is termed "low T3 syndrome" and is thought to be the result of decreased conversion of T4 to T3. Factors in acute illness that inhibit peripheral deiodination include high endogenous cortisol levels, inflammatory cytokines (eg, tumor necrosis factor), starvation, and certain medications (eg, glucocorticoids, amiodarone). TSH and T4 levels are often normal in ESS, although they also may fall in severe or prolonged cases; thus, ESS may represent a transient central hypothyroidism rather than a true euthyroid state. In light of these changes, thyroid function tests must be interpreted with caution in acutely ill patients. ESS does not usually require treatment, and abnormal results should be followed up with repeat testing once the patient has returned to baseline health. (Choices A and C) Hospitalized patients, particularly those in intensive care units, can have reduced levels of plasma binding proteins (eg, thyroxine-binding protein, transthyretin, albumin). Because most T4 circulates in bound form, this leads to a significant drop in total T4 levels, although free hormone levels are unaffected. The serum (total) T4 level is normal in this patient. (Choice D) Thyroid hormones undergo significant enterohepatic circulation, with reabsorption in the jejunum and upper ileum. Excessive fecal loss of thyroid hormone can occur in small intestinal disease (eg, Crohn disease, celiac disease). Ulcerative colitis does not directly involve the small intestine and is unlikely to affect reabsorption. (Choice E) Iodine deficiency can cause primary hypothyroidism, characterized by elevated TSH and low T4 levels. (Choice F) Only 15%-20% of circulating T3 is produced directly by the thyroid gland; decreased secretion from the thyroid gland is not a major contributor to low T3 in ESS. Educational objective: Euthyroid sick syndrome is characterized by low T3 levels with normal TSH and T4 in patients with acute illness. It is due primarily to decreased peripheral conversion of T4 to T3. Treatment is generally not recommended unless abnormal thyroid function persists after the patient has returned to baseline health. References: Euthyroid sick syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/27065175)

A 64-Year-Old Man Comes to the Hospital Due to Fever