Scientists have long believed there are overlapping central pain pathways in fibromyalgia (FM) patients and patients with neuropathic pain. Three pharmacologic therapies used to treat neuropathic pain—pregabalin, duloxetine and milnacipran—are FDA-approved to treat FM. However, these drugs only work well in 30-50% of patients and reduce pain by similar percentages.
A recent multicenter, randomized control trial has found that administering TENS (Transcutaneous Electrical Nerve Stimulation) to FM patients during physical activity significantly improves activity-induced and resting pain and fatigue and lessens disease impact. The FAST (Fibromyalgia Activity Study with TENS) trial is one of the first research efforts to investigate use with FM patients.
“The mechanisms by which TENS reduces pain… are exactly the communication abnormalities that exist in patients with fibromyalgia.”
“There was very good pre-clinical rationale for doing the study,” said Leslie Crofford, M.D., division chief of rheumatology and immunology at Vanderbilt University Medical Center and principal investigator on the new trial. “Earlier work done by some of my colleagues demonstrates that the mechanisms by which TENS reduces pain—how it affects the communication between the body and the spinal cord and the brain—are exactly the communication abnormalities that exist in patients with fibromyalgia.”
TENS vs. TENS Placebo
The study was limited to women, for whom FM is more common, and required a large homogeneous cohort. A total of 301 women aged 18-70 with reported FM pain ≥4 out of 10 were randomly assigned to active TENS, placebo TENS or no TENS treatment. Study staff were blinded to all three groups.
“One of our colleagues had previously developed a placebo TENS unit,” Crofford explained, “which was used to offset the substantial placebo effect inherent in this type of study.”
Patients continued taking any existing medications. They were asked not to change medications and not to start a new exercise program, including yoga or Tai Chi, or to have other treatment that might confound study interpretation. The cohort was stratified by whether patients were taking opioid medications.
“We did this because there’s a theoretical concern that patients on opioids might not have the same response. In fact, we did not see that. All the patients, no matter whether they were in the opioid or non-opioid strata, responded to the treatment equally,” Crofford said.
Active TENS was applied on the upper and lower back at a mixed frequency, with strong but comfortable intensity. Placebo TENS was applied in the same manner as active but delivered as an electrical current. The no-TENS group wore a non-active TENS unit. Pain and fatigue were measured during a six-minute walk test under supervision of study staff, and after one month of home use.
“We measured pain with movement while the TENS unit was on, because we thought that the main effect of the TENS unit only occurred then,” Crofford said. “We wondered if we let people use TENS regularly over the course of a month we would reduce resting pain. We were very pleased to see that it was in fact true.”
Next in TENS for FM Research
The current study results are not yet published. Crofford hopes that in future research, the team can demonstrate whether consistent use of TENS actually changes the physiology of the communication between the body, spinal cord and brain that is so characteristic of FM.
“What I’d like to do, and one of the reasons that we and others think it’s very important to reduce pain during activity, is to normalize the way patients move and behave,” she said. “We want to know if the use of TENS will allow patients to be more compliant with their exercise prescriptions.”