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Results indicate the potential relevance of pressure pain thresholds for understanding the mechanisms that contribute to pain in fibromyalgia.
Treatment with transcutaneous electrical nerve stimulation (TENS) for 4 weeks demonstrated improved pressure pain thresholds (PPT) in a cohort of female patients with fibromyalgia who experienced clinically relevant improvements, defined as a ≥30% reduction in self-reported movement-evoked pain (MEP), according to a study published in The Journal of Pain.1
However, the treatment did not improve continued pain modulation (CPM) in this patient population and no added improvements in PPT were reported following an 8-week period of active TENS use.
Patients with fibromyalgia tend to demonstrate alternations in pain processing, as indicated by reduced central pain inhibition (CPM), lower PPT, and augmented central pain facilitation, making the clinical management of the condition difficult. However, previous research has showed treatment with TENS was able to achieve clinically relevant improvements in pain and fatigue in approximately half of patients with fibromyalgia.2
“A single bout of TENS restores CPM and increases PPT locally at the site of TENS administration and at remote sites from the active treatment indicating systemic effects,” wrote Giovanni Berardi, PhD, PT, physical therapist at the Department of Physical Therapy and Rehabilitation Science, University of Iowa, and colleagues. “These improvements occur during and immediately after TENS use; however, the effects of repeated TENS use on PPT and CPM are unknown.”
To examine the influence of this treatment, data was collected from the Fibromyalgia Activity Study with TENS trial. Eligible subjects were randomized to receive active TENS (n = 76), placebo TENS (n = 68), or no TENS (n = 94) for a 4-week period. Those allocated to the active cohort continued to receive treatment for an additional 4 weeks (n = 66), while the other groups transitioned to active TENS (n = 161).
Per protocol, TENS was applied using butterfly electrodes to the upper and lower back using a modulated alternating frequency between 2 and 125 Hz, variable pulse duration, and the highest intensity deemed tolerable by patients. Subjects used the TENS unit for 2 hours per day, with single bouts lasting ≥30 minutes.
Investigators analyzed MEP, PPT, CPM, and resting pain prior- and post-treatment. Self-reported pain intensity was evaluated at rest and during a 6-minute walk test (6MWT), while symptom severity and widespread pain were assessed using the American College of Rheumatology 2010 Fibromyalgia Diagnostic Survey Criteria.
A total of 100 patients were categorized as TENS responders in both active and delayed cohorts. No significant changes in PPT or CPM were observed among patients in the active, placebo, or control TENS groups at the 4-week mark. However, patients who had ≥30% reductions in MEP had increases in PPT when compared with MEP non-responders (MEP responders: 25.1 ± 52.6%, MEP non-responders: 2.0 ± 39.8%, P <.001). No significant links between changes in PPT or CPM compared with MEP and resting pain post-TENS treatment were observed.
Investigators cited the small sample size of the active TENS groups during the 8-week treatment period as a limitation and encourage future research evaluating changes in PPT and CPM in a larger cohort over a longer timeframe. Further, results may not be generalizable to the greater fibromyalgia population as patients recruited into the study were morbidly obese.
“TENS activates descending inhibitory pathways to reduce pain including central inhibitory and excitatory pathways, while PPT and CPM assessment may provide insight into these underlying mechanisms contributing to pain, only PPT may change with intervention and both measures are inconsistently related to clinical pain in individuals with FM,” investigators concluded.