27-year-old man • muscle weakness • fatigue • electrolyte abnormalities • Dx?

Based on the results of the dexamethasone suppression test, a pituitary adenoma was unlikely (as they are often suppressed to < 5 mcg/dL with this test). The patient’s morning ACTH results came back as elevated (356.6 pg/mL; normal range, 10-60 pg/mL), suggesting inappropriate ACTH secretion, which most often has an ectopic source. However, a nuclear medicine octreotide scan and multiple computed tomography scans failed to locate such a source.

The patient eventually underwent bilateral petrosal venous sinus sampling to definitively rule out a pituitary source. Lastly, he underwent nuclear medicine positron emission tomography, which identified a nodular opacity in the anterior left lung apex, demonstrating moderate radiotracer activity (FIGURE 1).

THE DISCUSSION

Cushing syndrome is rarely encountered—it is estimated to affect 2% of patients with uncontrolled diabetes¹ and 1% of those with uncontrolled hypertension²—and requires a high level of clinical suspicion. This case highlights the importance of considering secondary causes of diabetes in patients who present atypically. This patient presented with symptoms consistent with Cushing syndrome that went unrecognized initially; these included high blood pressure, rounded face, weak muscles, hypokalemia, and intermittent hypernatremia in addition to new-onset hyperglycemia.^2-5 Despite the atypical findings, evaluation for diabetes and potential secondary causes was neglected until an ED evaluation 1 month after initial presentation. The work-up for possible Cushing syndrome was completed in the hospital but could easily have been conducted in the outpatient setting.

Making the diagnosis. When Cushing syndrome is suspected, consider consultation with Endocrinology. It is important to exclude exogenous glucocorticoid exposure through a thorough review of the patient’s medications.² The Endocrine Society² recommends that one of the following tests be performed:

• 24-hour urine free cortisol (≥ 2 tests)
• Overnight 1-mg dexamethasone suppression test
• Late-night salivary cortisol test.

Results within normal range make Cushing syndrome an unlikely diagnosis; however, for patients with suggestive clinical features, further work-up may be warranted.

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