A 52-year-old man comes to the office due to fatigue and muscle pain over the last several months. He has also experienced weight gain, dry skin, daytime sleepiness, and erectile dysfunction. Medical history is notable for hypertension treated with enalapril, hypercholesterolemia treated with rosuvastatin, and a nonfunctioning pituitary adenoma that was treated with trans-sphenoidal resection followed by radiation therapy 8 years ago. MRI 8 months ago showed a stable, 5-mm, residual pituitary mass. He has no headaches, vision loss, dark stools, or shortness of breath. The patient does not drink alcohol but has a 20-pack-year smoking history.
Blood pressure is 130/80 mm Hg and pulse is 58/min with no orthostatic changes. BMI is 29 kg/m². The remainder of the physical examination (including peripheral vision, testes, and thyroid) is normal.
Laboratory results are as follows:
Which of the following tests is most helpful in establishing this patient's diagnosis?

Question

A 52-year-old man comes to the office due to fatigue and muscle pain over the last several months. He has also experienced weight gain, dry skin, daytime sleepiness, and erectile dysfunction. Medical history is notable for hypertension treated with enalapril, hypercholesterolemia treated with rosuvastatin, and a nonfunctioning pituitary adenoma that was treated with trans-sphenoidal resection followed by radiation therapy 8 years ago. MRI 8 months ago showed a stable, 5-mm, residual pituitary mass. He has no headaches, vision loss, dark stools, or shortness of breath. The patient does not drink alcohol but has a 20-pack-year smoking history.
Blood pressure is 130/80 mm Hg and pulse is 58/min with no orthostatic changes. BMI is 29 kg/m². The remainder of the physical examination (including peripheral vision, testes, and thyroid) is normal.
Laboratory results are as follows:

Which of the following tests is most helpful in establishing this patient's diagnosis?

Quizplus · Accepted Answer

11ec193a_97bf_f564_853d_83648f53b684_MD0002_00 This patient's clinical findings (eg, fatigue, weight gain, dry skin, hyponatremia, normocytic anemia) are suggestive of hypothyroidism, but his TSH is not elevated. In light of his history of pituitary radiation, this presentation likely represents central hypothyroidism. In primary hypothyroidism TSH is usually elevated, but in central hypothyroidism TSH is typically low or inappropriately normal (although it may occasionally be mildly high in patients who secrete biologically inactive TSH). A low serum free T4 can confirm the diagnosis of central hypothyroidism. Pituitary masses are the most common cause of central hypothyroidism, due to direct compression by the tumor or late effects of surgery or radiation therapy. If the cause is not known, patients should undergo MRI of the pituitary to rule out a mass lesion. Patients with central hypothyroidism should also be tested for abnormalities of other pituitary hormones (eg, ACTH, growth hormone, gonadotropins). The treatment is levothyroxine with the dose adjusted to maintain free T4 in the high-normal range. Unlike in primary hypothyroidism, TSH is not used to monitor therapy as it will remain low. (Choice A) Prior to initiation of levothyroxine therapy, patients require a cosyntropin (synthetic ACTH) stimulation test, as levothyroxine can accelerate cortisol metabolism and precipitate adrenal crisis in patients with concurrent adrenal insufficiency. However, this patient's normal morning cortisol makes adrenal deficiency unlikely, and this test is not needed until central hypothyroidism is confirmed. (Choice C) Thyroperoxidase antibodies are seen in chronic lymphocytic (Hashimoto) thyroiditis, which typically presents with primary hypothyroidism and elevated TSH. (Choice D) Obstructive sleep apnea can cause fatigue and daytime sleepiness but is unlikely to cause dry skin, myalgias, hyponatremia, anemia, and bradycardia. (Choice E) Hypogonadism can cause fatigue and erectile dysfunction, but this patient's myalgias, dry skin, anemia, and hyponatremia are more consistent with hypothyroidism. In addition, hypothyroidism can suppress testosterone levels and may complicate the diagnosis of hypogonadism until the hypothyroidism is adequately treated. Educational objective: Central hypothyroidism is characterized by low (or inappropriately normal) TSH and low free T4. Evaluation should include MRI of the pituitary to rule out a mass lesion and testing for additional pituitary hormone deficiencies. The treatment is levothyroxine with the dose adjusted to maintain free T4 in the high-normal range. __________ References: Clinical review: central hypothyroidism: pathogenic, diagnostic, and therapeutic challenges. (http://www.ncbi.nlm.nih.gov/pubmed/22851492)

A 52-Year-Old Man Comes to the Office Due to Fatigue