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A 62-year-old woman is evaluated for an incidentally discovered left adrenal mass. Two weeks ago, the patient was evaluated in the emergency department for diffuse abdominal pain and vomiting. A CT scan was obtained that was normal except for the adrenal mass. Three hours after presentation to the emergency department, the pain resolved spontaneously.

Her medical history is significant for diet-controlled type 2 diabetes mellitus diagnosed 1 year ago and osteoporosis diagnosed 4 years ago. Her only medication is alendronate.

On physical examination, temperature is 37.0 °C (98.6 °F), blood pressure is 120/80 mm Hg, and pulse rate is 70/min. BMI is 26. The remainder of the physical examination is normal.

Laboratory evaluation reveals a serum sodium level of 139 mEq/L (139 mmol/L) and serum potassium level of 4.1 mEq/L (4.1 mmol/L). The previously obtained CT scan shows a 2.0-cm well-circumscribed, left adrenal lesion with a density of 5 Hounsfield units.

In addition to screening tests for pheochromocytoma, which of the following is the most appropriate diagnostic test to perform next?

A. Adrenal vein sampling
B. Low-dose dexamethasone suppression test
C. Plasma renin activity and aldosterone concentration measurement
D. No further testing

MKSAP Answer and Critique

The correct answer is B. Low-dose dexamethasone suppression test.

The most appropriate diagnostic test to perform next is the low-dose dexamethasone suppression test to screen for the autonomous secretion of cortisol. The increasing use of imaging studies for various medical indications has revealed otherwise unrecognized adrenal masses in less than 1% of the population younger than 30 years and up to 7% of those older than 70 years. Ten to 15% of adrenal incidentalomas are functional, although most have no overt clinical manifestations. Therefore, testing is usually necessary to identify functional tumors secreting catecholamines, cortisol, or aldosterone. Of the functional adenomas, most secrete excessive amounts of cortisol. In subclinical Cushing syndrome (CS), classic signs or symptoms of cortisol excess are not observed; however, complications of long-standing hypercortisolism may result. The patient has two disorders that can be seen in association with subclinical CS: type 2 diabetes mellitus and osteoporosis. Obesity and hypertension are also common. The low-dose overnight dexamethasone suppression test is recommended as the initial screening test for this condition due to its high sensitivity. Screening for pheochromocytoma, such as by measuring 24-hour urine fractionated metanephrines and catecholamines, is also indicated in all patients with an incidentally noted adrenal mass.

Adrenal vein sampling (AVS) is not needed. AVS is most often performed to evaluate for a bilateral versus unilateral adrenal cause of primary hyperaldosteronism.

Measurement of plasma renin activity and aldosterone concentration is not indicated in patients without hypertension.

No further testing is also inappropriate. Although the imaging characteristics of the mass are in keeping with a benign adrenal adenoma, further diagnostic evaluation is needed. This includes testing for autonomous hormonal secretion and subsequent radiographic surveillance (first at 3-6 months and then annually for 1-2 years).

Key Point

• Ten to 15% of adrenal incidentalomas are functional; biochemical testing is needed to identify functional tumors secreting catecholamines, cortisol, or aldosterone.

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