MON-539 - Mild Autonomous Cortisol Secretion in Pheochromocytoma: Prevalence, Clinical Implications, and Perioperative Outcomes at a Tertiary Care Center

Background: Pheochromocytomas (PCC) are rare neuroendocrine tumors arising from adrenal chromaffin cells, diagnosed as adrenal incidentalomas (AI), based on clinical suspicion, or through genetic syndrome screening. Biochemical workup mandatorily includes metanephrine measurement; however, the 1-mg overnight dexamethasone suppression test (DST), used to screen for mild autonomous cortisol secretion (MACS), is traditionally restricted to the AI setting. Glucocorticoid excess in PCC has been associated with adrenal cortical-medullary interactions and may contribute to hypothalamic-pituitary-adrenal (HPA) axis suppression, increased cardiometabolic burden, and perioperative complications. Only one study has systematically evaluated MACS prevalence in PCC, reporting cortisol nonsuppression in 24.5% of patients, associated with increased perioperative risk, higher diabetes prevalence, and larger tumor size.

Objective: To evaluate MACS prevalence in PCC and its clinical, biochemical, and surgical implications at a tertiary referral center.

Methods: Retrospective cohort of 18 histologically confirmed PCC patients followed at Santa Casa de Belo Horizonte, Brazil. Patients undergoing DST were stratified into suppressive (cortisol ≤ 1.8 µg/dL) and MACS (cortisol >1.8 µg/dL) groups. Descriptive and comparative analyses used Welch t-test, Mann-Whitney U test, Spearman correlation, and Fisher exact test (p < 0.05).

Results: DST was not performed in 6/18 patients (33.3%) diagnosed through clinical presentation or genetic screening. Among the 12 inidividuals who were tested, 5 (41.7%) were classified as MACS and 7 (58.3%) as suppressive. The MACS group showed lower basal ACTH (12.4±6.3 vs. 25.2±15.0 pg/mL; p=0.075), with ACTH < 10 pg/mL in 3/5 individuals, suggesting HPA axis suppression. A moderate negative correlation between post-DST cortisol and basal ACTH was observed (ρ=−0.545; p=0.067). No significant differences were found in tumor size (53.4±41.2 vs. 41.4±25.5 mm; p=0.585), age at diagnosis (59.0±16.0 vs. 61.7±16.5 years; p=0.781), or diabetes prevalence (60% vs. 71.4%; p=1.00). Glucocorticoids were used postoperatively exclusively in the MACS group (50% vs. 0%; p=0.109), with combined adverse outcome (complication and/or glucocorticoid use) in 75% vs. 28.6% (OR=7.5). Urinary normetanephrine levels were significantly higher in MACS (median 4.32 vs. 0.50× ULN; p=0.016).

Conclusion: MACS prevalence in PCC was 41.7%, with a trend toward basal ACTH suppression and greater perioperative glucocorticoid requirement. Non-screening in 33.3% of cases reflects conventional practice of the non-AI diagnostic context and highlights a clinically relevant gap. Despite the limited sample size, a recognized study limitation, these findings support routine DST screening in all PCC patients, regardless of diagnostic context or tumor size.

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