Ultra-low frequency electric currents reduced perceived lower back pain by 90 percent in a group of 18 patients, scientists report August 25 in Science Translational Medicine.
“The changes in pain scores are impressive,” says Jeremy Walker, an anesthesiologist at Vanderbilt University Medical Center who was not involved in the study. “While I would have some concerns about the long-term effects . . . the degree of pain relief certainly justifies further study.”
Most treatments for pain are pharmaceutical, but unfortunately these drugs can come with serious side effects, including the risk of developing a substance use disorder. So Stephen McMahon, a physiologist at King’s College London, and his colleagues decided to take a different approach: using electricity to tweak how pain neurons behave.
This is far from the first time electrical stimulation has been used to modulate neuronal firing. Deep brain stimulation—where an electrode is inserted far in the brain so it can deliver pulses that tell certain neurons to fire and release neurotransmitters—has been used for decades to treat Parkinson’s disease, for example. Some groups have even tried a similar technique to stimulate nerves in the spinal cord to manage pain, but results have been mixed.
McMahon, the senior author of the new study, says that’s because controlling pain requires a different stimulation strategy than treating diseases such as Parkinson’s. “Most neurostimulation is little pulses of electricity that excite things, but then you have to turn the excitation into inhibition if you’re trying to control pain,” he explains.
Direct currents, which flow continuously in a single direction for much longer than the millisecond-long pulses of the neurons themselves, can switch them off, but such relentless stimulation can cause tissue damage if repeated long-term.
So McMahon and his team tried a different approach: a current that alternates at an ultra-low frequency, which he says should mimic the suppressive effects of a direct current without damaging tissues.
The team started the study in rats. As hypothesized, delivering slow pulses to the spinal nerves of the animals successfully blocked neuronal signals associated with pain.
The researchers then tested the technique on 20 people with lower back pain. There was no control group. The team implanted electrodes along the participants’ lower spinal cords, which connected to a current-generating belt. Then, they programmed the devices to deliver ultra-low frequency pulses of electricity throughout the day; over the course of the two-week treatment period, each patient checked in with the researchers every few days to report their pain level and for adjustments to the stimulation program as needed. Two patients dropped out due to infections at the implantation site. The participants that completed the trial received between 249.5 and 336.4 hours of electrical stimulation over the 15 days.
Within hours, many of the patients started reporting improvements in pain scores. After 15 days, they reported feeling 90 percent less back pain on average and said it was easier to walk and otherwise move around.
“This is an advance over other electrical stimulation approaches, as it avoids using direct current which can lead to neuronal damage,” says Laura Bohn, a molecular biologist and neuroscientist at the Scripps Research Institute who was not involved in the study.
But, Bohn warns, “it isn’t clear . . . whether continuous use would lead to a loss of efficacy over a longer time period or whether damage could arise.”
The effects quickly wore off after the researchers removed the electrodes on day 15; a week later, the participants rated their pain to be 72 percent as intense as it was before starting the treatment. As of yet, there isn’t any data on the effects of continued ultra-low frequency electrical stimulation.
“Statistically, I think it is a very a very amazing finding,” says McMahon, but he admits the study’s size and lack of randomization are limitations. “We definitely need to make sure that [the findings] hold in the real world, in large populations, over long periods of time.”
Still, he says the most exciting part is that the “the effects are just black and white. . . . It is pretty amazing [that] you have this level of control.”