Review Question - QID 109472

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Cushing Syndrome / Disease DIAGNOSIS Diagnostic criteria QID: 109472 (M2.EC.17.4830)

QID 109472 (Type "109472" in App Search)

A 65-year-old obese man presents to his primary care clinic feeling weak. He was in the military and stationed in Vietnam in his youth. His current weakness gradually worsened to the point that he had to call his son to help him stand to get on the ambulance. He smokes a pack of cigarettes every day and drinks a bottle of vodka a week. He has been admitted for alcohol withdrawal multiple times and has been occasionally taking thiamine, folic acid, and naltrexone. He denies taking steroids. His temperature is 98°F (36.7°C), blood pressure is 170/90 mmHg, pulse is 75/min, and respirations are 20/min. He is obese with a significant pannus. Hepatomegaly is not appreciable. Abdominal striae are present. His workup is notable for the following:

Serum:
Na+: 142 mEq/L
Cl-: 102 mEq/L
K+: 3.9 mEq/L
HCO3-: 25 mEq/L
BUN: 24 mg/dL
Glucose: 292 mg/dL
Creatinine: 1.5 mg/dL
Ca2+: 10.1 mg/dL
AST: 7 U/L
ALT: 14 U/L
24-hour urinary cortisol: 400 µg (reference range < 300 µg)
Serum cortisol: 45 pg/mL (reference range < 15 pg/mL)

A 48-hour high dose dexamethasone suppression trial shows that his serum cortisol levels partially decrease to 25 pg/mL and his adrenocorticotropin-releasing hormone (ACTH) level decreases from 10 to 6 pg/mL (reference range > 5 pg/mL). What is the best next step in management?

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CT of the chest

11%

20/177

MRI of the adrenal glands

32%

57/177

MRI of the pituitary gland

49%

86/177

Low-dose dexamethasone therapy for 3 months

8/177

High-dose dexamethasone therapy for 3 months

2/177

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This veteran's laboratory workup is consistent with hypercortisolism. His partial responsiveness to the high dose dexamethasone suppression test suggests a pituitary tumor which merits imaging - MRI of the pituitary gland.

In normal patients, dexamethasone inhibits corticotropin releasing hormone and ACTH, thus decreasing cortisol. No response to the dexamethasone suppression test suggests either adrenal adenoma or an ectopic production of ACTH such as an ACTH-producing tumor. Decreased ACTH and cortisol levels in response to dexamethasone, as seen in this vignette, rules out an ectopic ACTH-producing tumor. The best next step in management is to image the pituitary gland either with CT or MRI.

Incorrect Answers:
Answer 1: CT of the chest would be indicated to evaluate for ectopic ACTH-producing tumors. The responsiveness to the dexamethasone suppression test makes this differential less likely.

Answer 2: MRI of the adrenal glands could be explored if ACTH levels were persistently low; in this case, ACTH was high but decreased with dexamethasone-mediated suppression.

Answers 4 & 5: Response to dexamethasone does not mean that therapy with dexamethasone is indicated. The underlying source of ACTH production must be addressed.

Bullet Summary:
In workup of hypercortisolism, pituitary tumors may respond partially or completely to high-dose dexamethasone suppression tests, whereas ectopic ACTH-producing tumors do not respond at all.

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