Endocrine Abstracts

Background: Diagnostic work-up for Cushing Syndrome (CS) can be challenging and is based on clinical and biochemical assessments. Once steroid excess is biochemically confirmed, the diagnostic serum ACTH threshold for determining ACTH-independent Cushing is debatable. A threshold of less than 15 ng/l has been adopted in our regional guidelines.

Aims: To investigate serum ACTH levels in patients with proven adrenal Cushing and to assess the clinical utility of 24-hour UFC and urine steroid profiling (USP) in the work-up for CS.

Methods: All patients undergoing unilateral adrenalectomy from January 2019 to February 2022 at the RVI were included. Data extracted: demographics, preoperative biochemical assessment, radiological & histological findings, post-operative short Synacthen test (SST)

Results: 27 patients had unilateral adrenalectomy for CS. F:M was 8:1 with a mean age of 59 years at diagnosis. 16 patients had a left-sided adrenal lesion, 10 had a right-sided one and 1 patient had bilateral lesions. Pre-operative random ACTH levels were <5, 5-9 and 10-12 in 56%, 37% and 7% of patients respectively. 22 patients had CS confirmed on either dynamic testing (20) or 24-hr UFC (1) or USP (1). The other 5 patients all failed their SST soon after surgery, thereby confirming previous adrenal Cushing. 24-hr UFC was elevated in only 36% of patients. USP was diagnostic in 25% of cases. Atrophy of the adrenal cortex was observed in 48% of resected adrenal glands. 3 patients passed their SST relatively soon post-surgery and histological examination in 2 out of these 3 cases demonstrated focally expanded or nodular adrenal cortex. 1 out of these 3 patients demonstrated ongoing steroid excess on biochemical retesting.

Conclusions: Majority of patients with adrenal Cushing have a random serum ACTH level of <10 ng/l. Pre-operative diagnostic yield from 24-hr UFC and USP is poor. Post-operative failed SST confirms prior ACTH-independent Cushing. For those patients who pass their SST soon after surgery, reassessment for steroid excess is warranted, especially if histology does not demonstrate atrophy of adrenal cortex.