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Renal Hypertension
Hypertension commonly complicates bilateral renal disease such as chronic glomerulonephritis, bilateral reflux nephropathy (chronic atrophic pyelonephritis of childhood), polycystic disease and analgesic nephropathy. Two main mechanisms are responsible:
- activation of the renin-angiotensin-aldosterone system
- retention of salt and water owing to impairment in excretory function, leading to an increase in blood volume and hence blood pressure.
Hypertension occurs earlier, is more common and tends to be more severe in patients with renal cortical disorders, such as glomerulonephritis, than in those with disorders affecting primarily the renal interstitium, such as reflux or analgesic nephropathy.
Bilateral renal disease
Meticulous control of the blood pressure is necessary to prevent further deterioration of renal function secondary to vascular changes produced by the hypertension itself. There is good evidence that ACE-inhibitor drug treatment confers an additional reno-protective effect for a given degree of blood pressure control than other hypotensive drugs.
Unilateral renal ischaemia results in a reduction in the pressure in afferent glomerular arterioles. This leads to an increase in the production and release of renin from the juxtaglomerular apparatus with a consequent increase in angiotensin II.
Treatment of Renal Hypertension
The aim of treatment is to correct hypertension and improve renal perfusion and excretory function.
The options in renal artery stenosis include transluminal angioplasty to dilate the stenotic region, insertion of stents across the stenosis (sometimes the only endoscopic option when the stenosis occurs close to the origin of the renal artery from the aorta, rendering angioplasty technically difficult or impossible), reconstructive vascular surgery and nephrectomy. With good selection of patients, in more than 50% hypertension is cured or improved by intervention.
Occasional dramatic improvements in renal function ensue but results are generally disappointing. No test can predict with satisfactory reliability the results of vascular surgery and many patients will do well on hypotensive therapy with or without surgery. ACE inhibitors must be avoided as hypotensive therapy as they can lead to acute renal failure in the presence of renal artery stenoses.
Unilateral renal disease
A small proportion of cases of hypertension are due to unilateral renal disease. The main causes are:
- unilateral renal artery stenosis due to fibromuscular hyperplasia (typically in young women) or atheroma in the elderly
- unilateral reflux nephropathy (atrophic pyelonephritis).
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