Propulsion with low-intensity ultrasound is showing promise as a safe and effective method for noninvasive repositioning of kidney stones, according to the findings of a first human feasibility study being conducted by researchers at the University of Washington, Seattle.
Taipei, Taiwan-Propulsion with low-intensity ultrasound is showing promise as a safe and effective method for noninvasive repositioning of kidney stones, according to the findings of a first human feasibility study being conducted by researchers at the University of Washington, Seattle.
First author Jonathan Harper, MD, reported on the initial clinical experience with the transcutaneous technique at the World Congress of Endourology and SWL in Taipei, Taiwan. The study is enrolling 15 patients representing three groups: patients with a history of successful passage of a previous stone and new, small de novo stones (<4 mm); those with fragments (<2 to 5 mm) post-lithotripsy; and patients scheduled to undergo surgery for removal of a larger stone (≥7 mm).
Reviewing outcomes for the first 10 patients, Dr. Harper reported the ultrasound procedure resulted in stone movement in all but one patient and without causing any pain or other adverse events during follow-up to 3 months.
Several patients passed their stones after the procedure, and in multiple patients thought to have a single large stone, the ultrasonic propulsion revealed that the mass was actually a collection of smaller stones.
“This is an early work in progress, but we are encouraged by our experience so far that indicates the technique has therapeutic and diagnostic potential,” said Dr. Harper, associate professor of urology at the University of Washington.
“Now, we will continue to evaluate it in more patients and are making further modifications in the settings to try to improve its performance.”
Dr. Harper explained that the motivation for developing this technique derived from recognition of the growing number of patients presenting with stone disease and two potential problems that can be encountered in their management. The first issue is the likelihood that post-lithotripsy stone fragments may remain in the kidney, where they may grow and become symptomatic over time. The second scenario involves patients with a larger stone causing ureteropelvic junction (UPJ) obstruction.
“We hypothesized that low-intensity ultrasound could offer a well-tolerated in-office procedure that could reposition small stones or fragments in order to enable their passing. In addition, we were interested in using it to dislodge a large stone obstructing the UPJ so that a patient requiring urgent intervention could schedule an elective procedure instead,” Dr. Harper said.
“Patients in our preoperative study arm are not obstructed. However, their inclusion gives us insight about the ability of ultrasound propulsion to reposition larger stones.”
He added that the identification of a diagnostic application of the procedure is exciting because it may allow some patients to avoid surgery.
“We had several patients who had been diagnosed by the radiologist as having a single large stone based on multiple imaging studies, including KUB, ultrasound, and even CT scan. These patients may be scheduled for surgery because they were thought to have a stone too large to pass. However, after ultrasonic propulsion, it was clear that the large stone was actually a collection of smaller pieces,” Dr. Harper said.
In the study, the propulsion is being performed with ultrasound outputs of either 50 V or 90 V, depending on the amount of tissue between the skin and target site. According to the protocol, a maximum of 40 push attempts can be performed.
“It only takes a few good pushes to move the stone if it is not attached to the urothelium. However, determining the angle to position the probe is a challenge that involves trial and error because the ultrasound does not provide 3-D architecture of the kidney, and it is particularly difficult to try to characterize the collecting system if it is collapsed because it is not well-hydrated,” Dr. Harper said.
He noted that it could not be determined whether some de novo stones that were harder to move were attached to the urothelium, within the parenchyma, or a false positive finding on ultrasound.
“However, in preoperative patients we have been able to confirm attachment of some harder-to-move stones, and that information gave us immediate gratification for understanding stone response,” Dr. Harper said.
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