Bilateral aldosterone-producing adenomas: differentiation from bilateral adrenal hyperplasia

Background: Primary aldosteronism (PA) is a common curable disease of secondary hypertension. Most such patients have either idiopathic bilateral adrenal hyperplasia (BAH) or unilateral aldosterone-producing adenoma (APA). Bilateral APAs are reportedly extremely rare. Aim: To compare the distinctive characteristics, clinical course, and outcomes of bilateral APA vs. BAH. Design: Retrospective record review. Methods: From July 1994 to Jan 2007, 190 patients diagnosed with PA underwent surgical intervention at our hospital. Bilateral APA was diagnosed in 7/164 patients with histologically-proven APA. Twenty-one patients diagnosed as BAH, and 21 randomly selected of unilateral APA patients, matched by age and sex served as controls. Results: Patients with bilateral APA had similar blood pressure, arterial blood gas analysis, spot urinary potassium to creatinine ratio and clinical symptoms to those with BAH, but lower serum potassium levels ( p = 0.027), lower plasma renin activity ( p = 0.037), and higher plasma aldosterone concentrations ( p = 0.029). Aldosterone-renin ratio (ARR) after administration of 50 mg captopril was higher in bilateral APA than in BAH patients ( p = 0.023), but not different between unilateral APA and BAH ( p = 0.218). A cut-off of ARR >100 ng/dl per ng/ml/h and plasma aldosterone >20 ng/dl after captopril significantly differentiated bilateral APA from BAH. Bilateral subtotal adrenalectomy normalized blood pressure and biochemistry in all patients with bilateral APA. Discussion: Bilateral APA, presenting simultaneously or sequentially, may not be a rare disease, accounting for 4.3% of APA in this sample. The clinical presentations of bilateral functional adenoma are not different from BAH, but patients with low serum potassium and ARR >100 after captopril should be carefully evaluated for bilateral adenoma.