Fixed-site high-frequency transcutaneous electrical nerve stimulation for treatment of chronic low back and lower extremity pain
Journal of Pain Research 2016:9 469–479
Objective: The objective of this study was to determine if fixed-site high-frequency transcutaneous electrical nerve stimulation (FS-TENS) is effective in treating chronic low back and lower extremity pain.
Background: Transcutaneous electrical nerve stimulation is widely used for treatment of chronic pain. General-purpose transcutaneous electrical nerve stimulation devices are designed for stimulation anywhere on the body and often cannot be used while the user is active or sleeping.
FS-TENS devices are designed for placement at a pre-determined location, which enables development of a wearable device for use over extended time periods.
Methods: Study participants with chronic low back and/or lower extremity pain self-administered an FS-TENS device for 60 days. Baseline, 30-, and 60-day follow-up data were obtained through an online questionnaire. The primary outcome measure was the patient global impression of change. Pain intensity and interference were assessed using the Brief Pain Inventory. Changes in use of concomitant pain medications were evaluated with a single-item global self-rating.
Results: One hundred and thirty participants were enrolled, with 88 completing the 60-day follow-up questionnaire. Most participants (73.9%) were 50 years of age or older. At baseline, low back pain was identified by 85.3%, lower extremity pain by 71.6%, and upper extremity pain by 62.5%. Participants reported widespread pain, at baseline, with a mean of 3.4 (standard deviation 1.1) pain sites. At the 60-day follow-up, 80.7% of participants reported that their chronic pain had improved and they were classified as responders. Baseline characteristics did not differentiate non-responders from responders. There were numerical trends toward reduced pain interference with walking ability and sleep, and greater pain relief in responders. There was a large difference in use of concomitant pain medications, with 80.3% of responders reporting a reduction compared to 11.8% of non-responders.
Conclusion: FS-TENS is a safe and effective option for treating chronic low back and lower extremity pain. These results motivate the use of FS-TENS in development of wearable analgesic devices.
Keywords: chronic pain, transcutaneous electrical nerve stimulation, wearable, patient global impression of change
The Functioning and Disability Supplement of the 2012 National Health Interview Survey estimated that 40 million US adults have pain every day or most days, and another 87 million have pain on some days.1 Many people with chronic pain also have low quality sleep, anxiety, depression, and poor overall health. The annual economic cost of chronic pain is US $600 billion in the US alone. The past few decades have seen a dramatic increase in use of prescription opioids for chronic pain despite concerns about their adverse effects and potential for addiction.
Therefore, there is a need for non-pharmacological options for treatment of chronic pain.
Transcutaneous electrical nerve stimulation (TENS) is the delivery of electricity across the intact surface of the skin to activate sensory nerve fibers. The technology was originally developed as a screening technique for predicting which chronic pain patients would respond to implantable stimulators. However, it became apparent that a significant percentage attained pain relief from TENS alone. Since that time, the efficacy of TENS for the treatment of chronic pain has been studied extensively. When evaluated with proper attention to methodological and technical factors, TENS has generally been shown to be safe and effective in various forms of chronic pain.
A conceptual model for how sensory nerve stimulation leads to pain relief was proposed by Melzack and Wall in 1965. Their theory stipulates that activation of sensory nerves (Aβ fibers) closes a “pain gate” in the spinal cord that inhibits the transmission of pain signals carried by nociceptive afferents (C and Aδ fibers) to the brain. In the past 20 years, anatomic pathways and molecular mechanisms that may underlie the pain gate have been identified. Sensory nerve stimulation activates the descending pain inhibition system, primarily the periaqueductal gray and rostroventral medial medulla located in the midbrain and medulla sections of the brainstem respectively.
The periaqueductal gray has neural projections to the rostroventral medial medulla, which in turn has diffuse bilateral projections into the spinal cord dorsal horn that inhibit ascending pain signal transmission.
General purpose TENS (GP-TENS) devices are designed to enable stimulation essentially anywhere on the body under the assumption that analgesia is limited to the vicinity of the electrodes. However, activation of descending inhibition leads to analgesia beyond the stimulation site. This suggests an alternative approach, fixed-site high-frequency TENS (FSTENS), in which the device is designed for a pre-determined location rather than according to the patient’s pain distribution.
A prior knowledge of the anatomy and neurophysiology of a target site enables development of wearable devices that can be used for extended time without disrupting daytime activity or sleep, which is not feasible with GP-TENS. For example, the mechanical design of the device can be optimized for the specific anatomical location. Similarly, the electrode dimensions and electrical specifications can be matched to the peripheral nerves to be stimulated. An emerging benefit of FS-TENS is integration of wearable technology such as accelerometers, gyroscopes, and thermosensors.
These measurements can provide objective feedback for therapy optimization, potentially in real-time. For example, accelerometer readings from the leg may be combined with a lower extremity biomechanical model to quantitatively track activity, falls, gait, and sleep, which are all influenced by chronic pain.
Finally, FS-TENS can better co-exist with other devices, such as pacemakers, that may be disturbed by nearby electrical stimulation.
Notes: Stimulator placed in band pocket. Electrode snapped to device through opening in band. Device placed on upper calf by wrapping band around leg.
Abbreviation: FS-TENS, fixed-site high-frequency transcutaneous electrical nerve stimulation.
This study evaluated the efficacy of an FS-TENS device, placed on the upper calf, for chronic low back and lower extremity pain. The first study aim was to determine whether this FS-TENS device was effective in providing pain relief.
The second aim was to identify baseline factors predictive of a positive response. The relationship between the anatomic distribution of pain and the response to FS-TENS was of particular interest. The third aim was to identify which chronic pain domains were most influenced by FS-TENS.
The implications of this study are that if FS-TENS is safe and effective, then opportunities exist for development of wearable analgesic devices for treating chronic pain.
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