By Rachel Zussman
Imagine being able to walk one moment and not the next. It’s a reality faced by roughly 100,000 individuals with complete or partial paraplegia in the United States. Yet, after more than 50 years of research, scientists have made little progress in treating the most severe spinal cord injuries, a harsh reality that frustrates patients and doctors alike. David Darrow, MD, University of Minnesota neurosurgery resident and MnDRIVE Neuromodulation Fellow, hopes to change this reality through an innovative use of epidural stimulation. It’s a treatment that uses electrical signals to stimulate damaged nerve cells and allow voluntary movement in patients with spinal cord injury.
Darrow focuses on the lower spinal cord, which contains the circuitry that allows us to walk. For years, doctors believed that the nerve fibers involved in movement were completely severed in paraplegic patients. However, newer research has shown that paraplegic patients still have a few remaining connected fibers.
“Alone, these fibers are not strong enough to communicate a signal to the brain,” explained Darrow. “But if we stimulate these fibers electrically, we should be able to generate enough power to allow voluntary movement.”
In Darrow’s clinical trial, surgeons implant a small, battery-powered device under the bone surrounding the spinal cord. The device sends signals along sensory pathways to the spinal cord and indirectly facilitates movement.
Inspired by promising results from a clinical trial run by Susan Harkema, Ph.D., associate scientific director of the University of Louisville Spinal Cord Injury Center, Darrow began designing his study in 2015. Last summer he began enrolling patients.
“Many previous trials have focused on walking,” Darrow said. “However, we are simply focused on the first step of movement. Voluntary movement opens up many doors to therapies that were previously impossible for patients who had no movement or sensation.”
In addition to the loss of voluntary movement, paraplegic patients frequently have issues relating to cardiovascular and autonomic function. Patients adapt to life in a wheelchair, yet struggle to overcome issues like blood pressure regulation and urinary function. Ideally, the neuromodulation device will stimulate damaged nerve cells to restore function and improve quality of life.
Fine-Tuning the Signals
Though the implantation of the device is relatively simple, each patient’s injury is different, making optimization extremely difficult. In the past, follow-up appointments took several hours, so doctors could only enroll a few patients in their trial if they still wished to practice clinically.
To improve efficiency for both patients and doctors, Darrow’s team designed an app that allows patients to test multiple stimulation settings at home. Using the app, each patient plays a game that prompts them to move their legs using various electrical settings. The data is sent directly to the University of Minnesota so Darrow can review the records and adjust the settings at monthly follow-up visits. With every appointment, Darrow gets closer to optimizing the patient’s device. Over time, Darrow’s team hopes to gather large amounts of quantitative data and determine which settings work best for each class of injury.
Two patients have received the device supplied by medical device maker Abbott. In both cases, patients immediately regained some voluntary movement. For one patient struggling with severe hypotension, the treatment helped restore her blood pressure to normal.
In partnership with Uzma Samadani, MD, Ph.D., at Hennepin County Medical Center, the team has plans to implant up to 100 devices, but Darrow hopes it will take far fewer to demonstrate that the treatment is effective and widely usable in paraplegic patients. He’s cautiously optimistic about the results of the trial.
“After 50 years of research with no real outcomes, it is exciting to see results,” said Darrow. “If we can just make patients 10 percent better by the end of the trial, we will be well on our way to chipping away at this life-changing diagnosis.”
Ultimately, he hopes neuromodulation will help doctors improve treatment results for paraplegic patients nationwide.
Rachel Zussman is a Biology, Society, and Environment major at the University of Minnesota’s College of Liberal Arts and an intern in the BioTechnology Institute’s Science Communications Lab.