Reninoma Masked by the Use of an Angiotensin Receptor Blocker.

Reninoma is a tumor that secretes excessive renin and is a rare cause of secondary hypertension. We report a case of reninoma with delayed diagnosis in a 33-year-old woman taking an angiotensin receptor blocker. During angiotensin receptor blocker medication, she had exhibited no electrolyte abnormality. The angiotensin receptor blocker was stopped for pregnancy planning purposes, and subsequent hypokalemia was observed. Abdominal computed tomography showed an enhanced round mass in the right kidney. Right partial nephrectomy was performed and the renal mass was removed. Histologic findings confirmed a diagnosis of reninoma. The patient's blood pressure and serum potassium remained normal after surgery. Diagnosis of reninoma might be delayed in patients taking angiotensin receptor blockers because they can mask hypokalemia due to reninoma.