A 46-year-old lady presented with a short history of thirst and polyuria. She had a past history of hypertension. Diabetes mellitus was ruled out as she had normal blood glucose levels. She was found to be normocalcaemic but hypokalaemic. In view of the latter finding and her hypertension, her plasma renin activity and aldosterone was measured, and found to be 45 pmol/ml/hr and 410 pmol/l respectively (aldosterone:PRA ratio of 9.1). The diagnosis of secondary hyperaldosteronism was made. Ultrasound scanning revealed a small left kidney. Magnetic resonance angiography revealed a 90% proximal stenosis of the left renal artery and an atrophic left kidney at 7.5 cm length. The right kidney and right renal artery were normal. Consequently, the cause of her secondary hyperaldosteronism was due to her unilateral renal artery stenosis and hyperreninaemia emanating from the left kidney. Secondary hyperaldosteronism causing thirst and polyuria is a relatively uncommon presentation of unilateral renal artery stenosis. Polydipsia and polyuria are caused by hypokalaemia-induced ADH resistance resulting in nephrogenic diabetes insipidus.
The aim of treatment is to preserve the function of the remaining kidney, with ACE inhibitors and angiotensin II receptor blockers being used to reduce aldosterone secretion, in combination with aldosterone receptor blockers such as spironolactone or eplerenone. Treatment by surgical revascularisation of the kidney affected by the stenosis has been described, as has nephrectomy of the non-functioning kidney. In our patients case, her BP and hypokalaemia have normalised on irbesartan and spironolactone, and the presenting complaints of polyuria and polydipsia have resolved.