P-002 Cyb11b2 Immunostaining- Enhancing the Clinical Management of Primary Aldosteronism

Abstract Introduction Unilateral primary aldosteronism (PA) is the most common surgically correctable cause of secondary hypertension. However, its diagnosis and subtyping remain challenging. In 2022, WHO recognized aldosterone-producing adenoma (APA) as a distinct pathological entity. Concurrently, the HISTALDO (Histopathology of Primary Aldosteronism) consensus introduced a standardized histopathological framework for aldosterone-producing lesions, centered on CYP11B2 immunohistochemistry (IHC), enabling accurate identification of hormonally active tumors. HISTALDO findings indicated that classical APAs, characterized by solitary CYP11B2-positive nodules, were associated with 95% postoperative biochemical success, in contrast with non-classical patterns. These findings underscore the prognostic value of standardized histopathologic classification. Clinical Case We present the case of a 61-year-old male with long-standing hypertension, who experienced sudden cardiac arrest due to ventricular fibrillation. Following resuscitation, hypokalemia was noted. Imaging revealed a 2 cm left adrenal mass, which exhibited significant contrast washout, features suggestive of a benign adenoma. The right adrenal gland showed mild micronodular thickening. Upon endocrinologic evaluation, the patient's medications included telmisartan, nebivolol, eplerenone and potassium supplementation. Despite treatment, the patient had persistent hypokalemia, suppressed renin and elevated aldosterone levels (702 pg/mL). Even though presence of a unilateral adrenal lesion cannot definitively exclude bilateral etiology of PA without adrenal venous sampling (AVS), due to the patient's clinical and biochemical instability, we suggested unilateral adrenalectomy. After surgery, potassium supplementation and eplerenone were discontinued. Subsequent biochemical evaluation demonstrated normalization of serum potassium, plasma aldosterone and renin levels. The initial histology report described a benign myelolipoma with cortical hyperplasia, which was conflicting with the patient's clinical presentation. Thus, a second histology review with CYP11B2 IHC was requested from an adrenal gland-specialized pathologist, which confirmed an aldosterone-producing adenoma with a central myelolipomatous component. These histological findings aligned with immediate postoperative biochemical recession, confirming that the hyperfunctioning adrenal gland had been appropriately removed. The patient remains stable after three years of follow-up. Conclusion This case highlights the clinical relevance of HISTALDO classification and CYP11B2 IHC in confirming diagnosis and predicting outcomes in unilateral PA. CYP11B2 IHC serves not only as a diagnostic marker but also as a predictor of surgical success that can guide postoperative expectations and follow-up strategies. Integrating this framework into routine clinical practice reinforces multidisciplinary collaboration and improves accuracy and effectiveness of care in patients with PA.Figure 1:Adrenal CT scan Table 1:Hormonal & Electrolyte Monitoring with Medication Adjustments (Pre-Operatively) Table 2:Hormonal & Electrolyte Monitoring with Medication Adjustments (Post-Operatively)