In the case of renal artery stenosis (RAS) — otherwise known as narrowed kidney arteries — the latest scientific evidence shows no clear advantage of angioplasty and stent placement over drug therapy, according to a new literature review funded by the Agency for Healthcare Research and Quality (AHRQ; Washington).

An article based on the review, completed by the agency’s Tufts-New England Medical Center Evidence-based Practice Center (Boston), is posted on the online version of the Annals of Internal Medicine.

“This is an important disease, and it affects a large number of people,” Jean Slutsky, director of AHRQ’s Center for Outcomes and Evidence, told Medical Device Daily. She said the review demonstrates that “unfortunately, we don’t have enough reliable evidence on this condition and the treatment of this condition to make very bold statements. And that, in and of itself, is an important finding.”

This is not good news since the numbers of patients attempting to deal with RAS grow with an aging “Boomer” population and the increase in those with diabetes. AHRQ said that atherosclerotic RAS, or ARAS, is a “progressive disease that may occur alone or in combination with hypertension and ischemic kidney disease.”

“The prevalence of ARAS ranges from 30% among patients with coronary artery disease to 50% among the elderly and those with diffuse atherosclerotic vascular diseases,” the AHRQ said. “In the U.S., 12% to 14% of new patients entering dialysis programs have been found to have ARAS.”

The agency said that Medicare data show that angioplasty more than doubled from 7,660 in 1996 to 18,520 in 2000. The average charge of RAS angioplasty done in the hospital was $27,800 in 2004, according to data from AHRQ’s Healthcare Cost and Utilization Project.

While many RAS patients are treated with drugs, a growing number of RAS patients are opting for angioplasty, AHRQ said. These patients have three treatment options: angioplasty, angioplasty in combination with a stent, or therapy with drugs, such as angiotensin converting enzyme (ACE) inhibitors or angiotensin-receptor blockers (ARBs), calcium channel blockers and/or beta blockers. Patients are sometimes placed on statins to lower cholesterol or antiplatelet medication, such as aspirin.

But there is no clear directive from the literature on how best to proceed, the researchers found.

For example, according to the Annals of Internal Medicine article, “No study directly compared aggressive medical therapy with angioplasty and stent placement.” Two studies that were randomized trials did compare angioplasty without stent and medical treatments, and along with eight other comparative studies and 46 cohort studies, but the methodologies employed were considered “weak” by the researchers.

Authors of the systematic literature review concluded that a shortage of direct comparisons between drug therapy and angioplasty has left important questions unanswered, such as which therapy is more likely to improve kidney function.

“In fact, we need to do more clinical studies about which treatments are optimal, which have the least side effects, and it’s an important fact to uncover that we need to know more before we can treat these patients with confidence and that one treatment is better than another,” Slutsky said.

The agency in its executive summary of the review noted that both the American College of Cardiology (Washington) and the American Heart Association (Dallas) have published guidelines recently for the management of patients with peripheral arterial disease, including those with RAS.

“These guidelines provide recommendations about which patients should be considered for revascularization; however, there remains considerable uncertainty on which intervention provides the best clinical outcomes,” the agency said in its summary of the literature review.

Those patients treated with drug therapy alone, for example, may face the risk of deterioration of kidney function, “with worsening morbidity and mortality.”

“Renal artery revascularization may provide immediate improvement in kidney function and blood pressure; however, as with all invasive interventions, it may result in substantial morbidity and mortality in some patients,” the agency said.

Currently, the agency said, the National Institutes of Health is sponsoring a large, multi-center trial, titled “Cardiovascular Outcomes in Renal Atherosclerotic Lesions (CORAL).” Patients are now being enrolled, although results aren’t expected until 2010.

The agency in its executive summary said that there are “additional topics of interest that the CORAL trial may be able to evaluate,” primarily through post hoc analyses, but it said that other studies may also be necessary.

Such studies include the “value of different diagnostic tests to determine which intervention would be best for individual patients; other baseline characteristics as predictors of relative outcomes,” as well as the “value of cointerventions at the time of angioplasty” or the differences in stent placement as well as alternative types of stents that could be used.

The study was completed under the Effective Health Care Program, launched in 2005 “to provide valid evidence about the comparative effectiveness of different medical interventions.”

“The object is to help consumers, healthcare providers and others in making informed choices among treatment alternatives,” AHRQ said in its executive summary.

The agency is particularly concerned with “appraisals of existing scientific evidence regarding treatments for high-priority health conditions,” thus generating new scientific evidence by “identifying gaps in existing scientific evidence and supporting new research.”