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ESSENTIALS OF DIAGNOSIS

  • Produced by atherosclerotic occlusive disease (80–90% of patients) or fibromuscular dysplasia (10–15%).

  • Hypertension.

  • AKI in patients starting ACE inhibitor therapy if stenosis is bilateral.

GENERAL CONSIDERATIONS

Atherosclerotic ischemic renal disease accounts for most cases of renal artery stenosis. Fibromuscular dysplasia is a less common cause of renal artery stenosis. Approximately 5% of Americans with hypertension suffer from renal artery stenosis. It occurs most commonly in those over 45 years of age with a history of atherosclerotic disease. Other risk factors include CKD, diabetes mellitus, tobacco use, and hypertension.

CLINICAL FINDINGS

A. Symptoms and Signs

Patients with atherosclerotic ischemic renal disease may have refractory hypertension, new-onset hypertension (in an older patient), pulmonary edema with poorly controlled blood pressure, and AKI upon starting an ACE inhibitor. In addition to hypertension, physical examination may reveal an audible abdominal bruit on the affected side. Fibromuscular dysplasia primarily affects young women. Unexplained hypertension in a woman younger than 40 years is a reason to screen for this disorder.

B. Laboratory Findings

BUN and serum creatinine may be elevated if there is significant renal ischemia. Patients with bilateral renal artery stenosis may have hypokalemia, a finding that reflects activation of the renin-angiotensin-aldosterone system in response to reduced blood flow (a “prerenal” state).

C. Imaging

Abdominal ultrasound can reveal either asymmetric kidney size if one renal artery is affected more than the other or small hyperechoic kidneys if both are affected.

Three prevailing methods used for screening are Doppler ultrasonography, CT angiography, and magnetic resonance angiography (MRA). According to the American College of Cardiology/American Heart Association guidelines, one of these should be undertaken if a corrective procedure would be performed when a positive test result is found. Doppler ultrasonography is highly sensitive and specific (85% and 92% respectively in a meta-analysis of 88 studies) and relatively inexpensive. However, this method is extremely operator and patient dependent, and may be a poor choice for patients who are obese, unable to lie supine or have interfering bowel.

CT angiography consists of intravenous digital subtraction angiography with arteriography. A noninvasive procedure, it uses a spiral (helical) CT scan with intravenous contrast injection. The sensitivities from various studies range from 77% to 98%, with specificities in the range of 90–94%.

MRA is an excellent but expensive way to screen for renal artery stenosis, particularly in those with atherosclerotic disease. Sensitivity is 77–100%, although one flawed study showed a sensitivity of only 62%. Specificity ranges from 71% to 96%. Turbulent blood flow can cause false-positive results. The imaging agent for MRA (gadolinium) has been associated with nephrogenic systemic fibrosis, which occurs primarily in patients with a GFR of less than 15 mL/min/1.73 m2, and rarely in patients with a GFR of 15–29 ...

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