Links between kidney stones, systemic conditions revealed

Multiple presentations at the 2011 AUA annual meeting will highlight associations between nephrolithiasis and systemic conditions, including cardiovascular disease.

"These studies add to previous evidence of associations between kidney stones and systemic diseases," said Dean Assimos, MD, professor of surgical sciences-urology at Wake Forest University in Winston-Salem, NC. "This story will continue to evolve, and it will be interesting to see what the evidence reveals about associations between kidney stones and systemic disease."

In one study, urinary markers of calcium oxalate stone formation correlated with higher scores on the Framingham cardiovascular risk-assessment scale. Investigators measured urinary levels of oxalate, calcium, citrate, uric acid, and creatinine in patients with calcium oxalate urolithiasis and a stone-free control group. Stone formers, both men and women, had higher urinary oxalate excretion and higher Framingham risk scores compared with the control group.

Another group of researchers assessed levels of various antioxidants among participants in the National Health and Nutrition Examination Survey (NHANES III). The analysis showed levels of alpha-carotene, beta-carotene, and beta-cryptoxanthin had significant inverse associations with kidney stones.

"Together, these studies reinforce previously reported associations between kidney stones and systemic disease," said Dr. Assimos. "The implication is that a healthy lifestyle may limit the risk of kidney stone formation."

Cystinuria is rare genetic disorder in which those afflicted develop cystine kidney stones. A study of patients attending a cystinuria clinic demonstrated that higher levels of ornithine, arginine, and lysine excretion (amino acids also excreted at high levels in this condition) were more predictive of kidney stone activity than cystine excretion.

Limitations of renal US exposed

Clinicians increasingly have turned to ultrasound to spare patients the radiation exposure associated with computed tomography. A comparison of CT and renal ultrasound for imaging patients with urolithiasis showed almost a 40% rate of discrepancy between the studies. About two-thirds of the discrepancies involved stones that were visualized by CT but not ultrasound. The findings illustrate some of the limitations of renal ultrasonography for evaluating stone patients, Dr. Assimos said.

A preclinical model of a novel stone-removal technology demonstrated the feasibility of using iron-based microparticles to render small calcium oxalate stone fragments paramagnetic and amenable to manipulation by magnetic instrumentation. Mice infused with the microparticles had some evidence of lung inflammation, but no particles or associated inflammation were seen in the bladder, brain, or kidneys. If the procedure's safety can be proven, this technology will be useful for the endoscopic removal of stone fragments, which can be tedious and time consuming, Dr. Assimos noted.

Lithotripsy ownership examined

The influence of physician ownership on decision making related to the use of lithotripsy has raised some concern about potential ethical conflicts. A review of a state ambulatory surgery database showed no decline in the use of ureteroscopy for stone removal following expansion of physician ownership of lithotripsy units.

A modification of the conventional prone positioning for percutaneous nephrolithotomy showed potential for increased facilitation of the procedures. Prone-flexed positioning lowers the kidneys in relation to the ribs, thereby minimizing the need for supracostal access.

"This is a nice technical pearl that I have started using since hearing about it from Dr. John Honey, the senior author of this study," said Dr. Assimos.

Preliminary testing of a prototype ultrasonic stone expulsion system demonstrated the feasibility of using focused ultrasound to displace stone fragments from the lower pole collecting system. This was studied in a porcine model, and there was no evidence of renal damage.

An initial clinical evaluation provided evidence of precise movement and improved maneuvering with a robotic flexible ureterorenoscopic surgical system. Outcomes in a small number of patients showed that intrarenal stones could be removed with ease and precision and in less time than required for conventional stone removal.

"This AUA meeting will provide a good overview of the many advances that are occurring in the field of stone disease," Dr. Assimos concluded.