Histopathological Diagnosis of Primary Aldosteronism Using CYP11B2 Immunohistochemistry

CONTEXT: Although primary aldosteronism (PA) is the most common cause of endocrine hypertension, histopathological methods to reveal the presence and sites of aldosterone overproduction remain to be established. OBJECTIVE: The objective of the study was to investigate the significance of immunohistochemical staining to detect CYP11B2 and CYP11B1 in adrenal tissue of patients with PA. DESIGN AND PATIENTS: Thirty-two patients with PA who underwent unilateral adrenalectomy were studied. Immunohistochemical staining was performed using anti-CYP11B2 and anti-CYP11B1 antibodies on paraffin-embedded sections. We analyzed the expression of each enzyme semiquantitatively by scoring staining intensity and correlating it with clinical findings. RESULTS: Twenty-two patients showed positive CYP11B2 immunostaining in their tumors (aldosterone producing adenoma, APA). Four patients with CYP11B2-negative unilateral adenomas and 4 patients without tumors on computed tomography showed aldosterone-producing cell clusters (APCCs) with CYP11B2 immunostaining in the zona glomerulosa (multiple APCCs). The remaining 2 patients had unilateral multiple adrenocortical micronodules and diffuse adrenocortical hyperplasia, respectively. In APA, CYP11B2 score adjusted for tumor volume was positively correlated with plasma aldosterone and negatively correlated with serum potassium. The APA group was divided into 3 subgroups based on relative CYP11B2 and CYP11B1 immunostaining levels. The CYP11B2/CYP11B1-equivalent and CYP11B1-dominant APA groups showed significantly higher serum cortisol after 1 mg dexamethasone and larger tumor size than the CYP11B2-dominant APA group. CONCLUSIONS: The present study clearly demonstrates that CYP11B2 immunostaining is a powerful tool for histopathological diagnosis of aldosterone overproduction in PA and for subtype classification of APA, multiple APCCs, unilateral multiple adrenocortical micronodules, and diffuse hyperplasia.