Hyponatraemic hypertensive syndrome (HHS) is associated with unilateral renal ischaemia1. It is characterised by resistant hypertension, elevated renin and aldosterone, pressure natriuresis with consequent hyponatraemia, hypokalaemia and volume depletion2.
A 48 year old woman presented with chronic hyponatraemia (Na 113-124 mmol/L [135-145]) and confusion. Background included hypertension (normotensive on olmesartan, lercanidipine, enalapril and moxonidine) and peripheral vascular disease. Serum sodium 131 mmol/L [135-145], osmolality 274 mOsm/kg [275-295], urine osmolality 212 mOsm/kg [300-900] and urinary sodium 53 mmol/L [N high ≤ 16]. Secondary causes of hyponatraemia were excluded (Cortisol 775 nmol/L [100-540], TSH 1.46 [0-12]). Olmesartan, enalapril and lercanidipine were withdrawn over 2 months. The patient deteriorated, requiring hospitalisation with increased confusion, hypertension (160/90mmHg sitting, 120/80mmHg standing), hyponatraemia (Na 113, serum osmolality 241 mOsm/kg, urine osmolality 229 mOsm/kg, urine sodium 11 mmol/L), hypokalaemia (2.7 mmol/L [3.2-5]), and acute kidney injury (eGFR 33 ml/min/1.73m2).
Serum aldosterone was increased (3435 pmol/L [80-1040]). 24 hour urine protein was elevated 20.42 g/day with negative nephrotic screen. Renal ultrasound demonstrated a hypoplastic left kidney (7.59cm) with absent renal artery flow. On day 4 the patient transferred to the intensive care unit with hypertensive encephalopathy requiring sedation. Sodium normalised over 12 hours with 3% hypertonic saline. Blood pressure was controlled following reintroduction of ACE inhibition (ramipril 10mg). Renal vein sampling revealed elevated plasma renin (> 8000 Fm/L/s [100-1500]) with right and left renal vein renin 7433 Fm/L/s and > 8000 Fm/L/s respectively. DTPA scan identified virtually non-functioning left kidney. Blood pressure, electrolytes, proteinuria and renal function improved with ramipril. This is consistent with HHS, driven by unilateral renal ischaemia.
HHS is underreported 3,4. The cornerstone of therapy is nephrectomy or blockade of renin angiotensin aldosterone system. Clinicians need to be aware of the phenomena and vigilant to the dangers of ceasing ACE blockade in such individuals.