Overworked Kidneys Tied to Stroke Risk

Harold Pretorius, MD, PhD, of the Cincinnati Cognitive Collaborative in Ohio, and colleagues reported at the World Congress on Insulin Resistance, Diabetes, and Cardiovascular Disease (WCIR) that, in a single-center study, 22% of patients with either condition who also had renal hyperfiltration, had a stroke.

Pretorius said, "If you divert blood flow away from the brain, adverse events like stroke are inevitable." He explained that the increased blood flow needed by the kidneys to work at such high rates of filtration may be pulling the blood supply away from the brain, which could have an impact on brain function and can also lead to these adverse events.

To examine their hypothesis, the group imaged cerebral flow reserve index (FRi) via brain SPECT, which has been shown to correlate with increased stroke risk in patients with metabolic syndrome or with diabetes patients who have decreased glomerular filtration rates (<60 ml/min-1.73m²). Currently, the imaging technology is FDA approved for confirming stroke, they said.

They assessed a total of 90 patients with renal hyperfiltration in their study. They found that 22% of these patients had experienced stroke, which was an incidence similar to that seen in previous trials of renal insufficiency patients at 14%, they said.

Almost half of renal hyperfiltration patients had metabolic syndrome and 36% had type 2 diabetes. Other characteristics associated with renal hyperfiltration include female sex (78%) and white ethnicity (74%).

As expected, there was a significant proportion of smokers (33%), the researchers said. But only 17% had coronary artery disease and that proportion was, "relatively lower than I would have expected," Pretorius said.

He added that many questions still remain regarding the implications of renal hyperfiltration. For instance, does the stroke risk in renal hyperfiltration correlate with mild cognitive impairment, and, if so, is the early form of dementia reversible because the hyperfiltration may be reversible?

Yehuda Handelsman, MD, president and medical director of WCIR, advised caution when interpreting the study results and added that, "I think it's an interesting hypothesis, but I think it's too early to draw any conclusions." "We've known for years now that hyperfiltration really starts before kidney problems start, so maybe there is already a change in the cardiovascular system -- whether what happens in the brain, or heart, or elsewhere starts also in the kidney."

"Maybe what you see is just a marker for something else happening in body," he added, "not necessarily causality."

Still, Pretorius and colleagues concluded that because renal hyperfiltration appears to be relatively common among patients with metabolic syndrome and type 2 diabetes, the stroke risk in these groups may also be higher.

• Explain that renal hyperfiltration may be associated with a greater risk of stroke, especially in patients with the metabolic syndrome or type 2 diabetes.
• Note that the study measured cerebral flow reserve index (FRi) by brain SPECT imaging.
• Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

Pretorius HT, et al "Renal hyperfiltration is associated with decreased cerebral flow reserve and increased stroke risk in patients with metabolic syndrome or diabetes mellitus" WCIR 2011.