False-positive results of adrenal venous sampling due to mild autonomous cortisol secretion in a patient with primary aldosteronism: a case report with review of literature.

We report the case of a 50-year-old female diagnosed with primary aldosteronism (PA) complicated with mild autonomous cortisol secretion (MACS). The patient had a 5-year history of hypertension, and screening revealed an elevated aldosterone-to-renin ratio (ARR). Although she demonstrated no clinical features of Cushing's syndrome, her serum potassium level was at the lower end of the normal range. The baseline plasma renin activity was <0.2 ng/mL/h, and the plasma aldosterone concentration was 165 pg/mL. Confirmatory tests supported the diagnosis of PA, and computed tomography (CT) revealed a 19-mm tumor in the left adrenal gland. Following a 1-mg dexamethasone suppression test, her serum cortisol level measured 9.0 μg/dL, and the diurnal rhythm of cortisol secretion was absent. Plasma adrenocorticotropic hormone (ACTH) was suppressed. Adrenal venous sampling (AVS) revealed right-sided dominance before and after ACTH stimulation, with lateralization indices of 43.8 and 5.0, respectively. Considering the findings, we prioritized treatment for MACS and performed left adrenalectomy. Hypertension and elevated ARR persisted postoperatively. Histopathological examination revealed a 26-mm CYP11B-positive and CYP11B2-negative adenoma. The surrounding adrenal cortex contained multiple CYP11B1-negative and CYP11B2-positive nodules and micronodules. This case was retrospectively considered to represent bilateral PA. The AVS interpretation was misleading owing to cortisol imbalance between the adrenal veins due to cortisol producing adenoma. Treatment strategies for patients with PA and concurrent MACS should encompass a comprehensive assessment of AVS and CT findings.