Patients with implanted devices for spinal cord stimulation (SCS) for whom paresthesia-based stimulation has failed to relieve pain may have an “effective alternative” in subperception stimulation at 1 kHz, a recent pilot study suggests.
The investigators conducted a prospective, randomized study (Neuromodulation2016 May 17. [Epub ahead of print]) to apply the findings of a study in a rat model (Anesthesiology 2013;119:422-432)—that showed the efficacy of high-frequency SCS in inhibiting mechanical hypersensitivity compared with sham or 50-Hz stimulation—to a human population.
“When the animal modeling demonstrated similar results at 1 kHz versus 10 kHz, it seemed logical that it would work similarly in humans,” said James North, MD, the study’s first author, and medical director of the Center for Clinical Research, Carolinas Pain Institute, in Winston-Salem, N.C.
The study included 22 patients who reported inadequate pain relief from paresthesia-based stimulation alone, based on a Numeric Pain Rating Scale (NPRS) score of less than 5. The patients were randomly assigned to two groups: The first group received 1-kHz subperception stimulation followed by paresthesia-based stimulation, and the second group received paresthesia-based stimulation followed by 1-kHz subperception stimulation. Each treatment was administered for three weeks, followed by a washout period between treatments lasting a week to 10 days. The primary outcome measure was NPRS scores. The patients also completed the Oswestry Disability Index (ODI) and Patient’s Global Impression of Change (PGIC) as secondary outcome measures.
In the trial, 21 patients (95%) reported improvements in average, best and worst pain scores. All NPRS scores for these three categories were significantly lower (better) with subperception stimulation compared with paresthesia-based stimulation (P<0.01, P<0.05 and P<0.05, respectively). The effectiveness of treatment was also significantly greater as indicated by both ODI (P=3.9737 × 10-5) and PGIC scores (P=3.0396 × 10-5), the investigators reported.
Each patient was given three SCS programs to choose from for the duration of treatment. All the participants remained on a single mode during 1-kHz subperception stimulation, but reported using all three programs during paresthesia-based stimulation, the researchers noted.
Dr. North said the findings did not surprise him. “What is exciting about this new approach is providing patients the option of paresthesia versus paresthesia-free stimulation,” he said.
Dr. North said most of his patients use a combination of both. “For example, a patient may use the 1-kHz subthreshold waveform during the day, then switch to traditional paresthesia-based stimulation when they get home and are watching TV at the end of a hard day,” Dr. North said. “Or it could be the exact opposite: The patient may use traditional settings during the day but then switch to subthreshold at night when they’re sleeping. They are in control.”
Timothy Deer, MD, president and CEO of the Center for Pain Relief Inc., in Charleston, W.Va., commented, “It is encouraging to see studies comparing different frequencies, waveforms and other variables. Many patients benefit from paresthesia-free stimulation, while some patients prefer paresthesia.”
While he “applauds” the pilot study, Dr. Deer cautioned that currently there is no long-term prospective study supporting the use of subperception SCS at 1 kHz.
“Three weeks in each arm is not adequate to measure function, pain relief or quality of life,” said Dr. Deer. He also recommended that future trials implement the use of closed-loop feedback technology in both study arms.
Dr. North noted that a larger trial is already underway, in which he is taking part. The WHISPER study, which is funded by Boston Scientific, is a multicenter, randomized, controlled, crossover, open-label study of 146 previously implanted patients that will document the efficacy of subperception SCS at up to 1.2 kHz. The protocol will be similar to the present study, he said, except the patients will be randomly assigned to each treatment arm for three months, and will be followed for one year.
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