Review Question - QID 100608

This patient's hypertension and abdominal bruit suggest renal artery stenosis, most likely fibromuscular dysplasia. Angiotensin-converting enzyme (ACE) inhibitors should be avoided in renal artery stenosis because of their effects on renal blood flow.

Renal artery stenosis results in a renin-mediated form of hypertension. Decreased blood flow to the juxtaglomerular apparatus leads to elevated renin and activation of the renin-angiotensin-aldosterone system. Renin stimulates the production of angiotensin I, which is converted to angiotensin II by ACE. Angiotensin II is a potent vasoconstrictor, especially of the efferent arteriole, and in a patient with renal artery stenosis, constriction of the efferent arteriole is crucial to maintain GFR and renal perfusion. When angiotensin II production falls (as with an ACE inhibitor), GFR and renal perfusion may precipitously drop. A decrease in GFR may be detected by a rise in serum creatinine.

Hartman et al. discuss the radiologic evaluation of suspected renovascular hypertension. Duplex doppler ultrasonography is a good screening test in many patients, but it has limitations in obese patients. For patients with normal renal function but a high clinical index of suspicion for renovascular disease, contrast-enhanced magnetic resonance angiography and computed tomographic angiography are the most accurate imaging tests.

Viera et al. discuss the diagnosis of secondary hypertension. A secondary etiology may be suggested by symptoms (e.g., flushing and sweating suggestive of pheochromocytoma), examination findings (e.g., a renal bruit suggestive of renal artery stenosis), or laboratory abnormalities (e.g., hypokalemia suggestive of aldosteronism).

Illustration A depicts the renin-angiotensin-aldosterone pathway. Renin, secreted from the juxtaglomerular apparatus, helps to convert angiotensinogen (made in the liver) to angiotensin I. Angiotensin I is converted in the lung by the angiotensin converting enzyme (ACE) to angiotensin II. Angiotensin II is a potent vasoconstrictor and also stimulates release of aldosterone.

Incorrect Answers:
Answer 1: Hydrochlorothiazide, a thiazide type diuretic, would be a reasonable approach to treating this patient's hypertension.
Answer 2: Atenolol, a beta-blocker, could also be used to treat this patient's hypertension.
Answer 3: Amlodipine, a calcium channel blocker, would be another potential option to treat this patient's hypertension.
Answer 4: Spironolactone, a potassium sparing diuretic, could be used in this patient, though would not be a first line option.