Primary aldosteronism due to unilateral adrenal hyperplasia: a case report

Primary aldosteronism is one of the differential diagnosis of secondary hypertension. This is usually caused by an aldosterone producing adenoma or bilateral adrenal hyperplasia which comprise about 65% and 30% of the cases, respectively. However, less than 1% of primary aldosteronism is caused by unilateral adrenal hyperplasia which is a relatively rare subset of primary aldosteronism. The clinical and biochemical manifestations of the disorder are indistinguishable from aldosterone-producing tumor, and a definitive diagnosis can only be made by pathological finding. A 33-year-old male Chinese patient presented with hypertension, hypokalemia, metabolic alkalosis, and the hypersecretion of aldosterone associated with suppressed plasma renin activity which is a typical hallmark of primary aldosteronism. Image studies including both magnetic resonance imaging (MRI) and 131I NIP-59 scan as well as postural test suggested an aldosterone-producing tumor of the right adrenal gland. Unilateral adrenectomy and pathological examination of the right adrenal gland eventually proved a case of unilateral adrenal hyperplasia. Blood pressure, plasma potassium, aldosterone and renin activity levels returned to normal two weeks after operation and had remained normal at up to one year of follow up. In addition, a saline loading test showed normal suppression of plasma aldosterone level one year after the operation, suggesting that the function of the left adrenal gland remains normal. The etiology of unilateral adrenal hyperplasia is unclear and the future recurrence of the disease is possible. Long-term follow-up is necessary to ensure the cure of this disorder.