Closed-Loop Stimulation More Effective for Chronic Back, Leg Pain

By Anne Harding

January 15, 2020

NEW YORK (Reuters Health) - Closed-loop spinal cord stimulation produces greater reductions in pain and medication use in patients with chronic, intractable back and leg pain than does open-loop stimulation, a new randomized controlled trial shows.

The study, in The Lancet Neurology, tested a device that measures evoked compound action potentials (ECAPs) and automatically adjusts the stimulation current for consistent spinal cord activation.

"This is a landmark study and a game-changer in neuromodulation," Dr. Nagy Mekhail of Cleveland Clinic in Ohio, the study's first author, told Reuters Health by phone. "This is the first time that we can listen to the spinal cord and talk to the neurons and have an interactive therapy."

Spinal cord stimulation has been used to treat chronic leg and back pain for more than five decades, Dr. Mekhail and his team note in their report. About half of patients are treated successfully, meaning their pain is reduced by at least 50%.

One major drawback of fixed stimulation, the authors point out, is that normal body movements constantly change the distance between the electrode and the spinal cord, causing large differences in spinal cord activation.

The Evoke System from Saluda Medical, which the new study tested, aims to avoid this problem by measuring ECAP with each pulse delivered and modulating the stimulation current to keep spinal cord activation in the patient's therapeutic window.

Following promising results from a single-arm study in patients with failed-back-surgery syndrome, investigators on the current trial randomized 134 patients at 13 U.S. clinics to receive ECAP-controlled, closed-loop stimulation with the Evoke System, or fixed-output, open-loop stimulation with the same system.

At three months, 82.3% of the closed-loop group had achieved the primary outcome of a 50% reduction in pain or more, versus 60.3% of the open-loop group (P=0.005).

At one year, 83.1% of closed-loop patients and 61.0% of open-loop patients had at least a 50% reduction in pain (P=0.006).

Patients receiving closed-loop stimulation also had greater improvements in mood and mental health. Among those who were using opioids at the study's outset, 55% of patients in the closed-loop group were able to reduce or stop their opioid use, versus 40% of the open-loop group.

About 60% of the patients in the study had failed-back-surgery syndrome, while the rest had not received surgical treatment, Dr. Mekhail noted. "The study underscores that there is a certain patient population that might benefit from neuromodulation without going through the hassle of surgery and the comorbidities that might be associated with surgery, and that would save the society a huge cost."

He and his colleagues are currently investigating the characteristics of the patients in the study who weren't treated surgically, and also comparing health care utilization in patients before and after treatment.

"The clinical investigation . . . is a major contribution to the literature and suggests that closed-loop spinal cord stimulation could be the future of pain control," Dr. Bizhan Aarabi of the University of Maryland School of Medicine in Baltimore writes in an editorial accompanying the study.

"The Evoke study sends a clear and positive message to clinicians that spinal cord stimulation can provide effective pain relief and control the suprasegmental aspects of failed back surgery syndrome relating to the affective-arousal part of the disorder," he adds. "The ability to adjust the waveform and set the ECAP at a specific level that is comfortable for the patient indicates the possibility of personalizing pain control and optimizing its management at an individual patient level."

Saluda Medical funded the study. Several of Dr. Mekhail's coauthors report financial ties to the company. SOURCE: https://bit.ly/2QVD9WZ and https://bit.ly/2QXOV2Z Lancet Neurology, online December 20, 2019.

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