Chronic pain is a significant problem for many individuals following spinal cord injury (SCI) and may have a major impact on their function and quality of life.1
For example, Nepomuceno et al
reported that 80% of 200 persons with SCI reported abnormal sensations and 48% reported sensations that were painful. Turner et al
similarly found that 79% of 384 persons with SCI experienced pain. Sixty-one percent reported bilateral pain below the level of injury, 41% reported pain above the injury, and 50% reported pain at the level of injury. Rintala et al
reported that 75% of 77 men with SCI reported chronic pain and more than 25% of these had more than one chronic pain component. These investigators also noted that the presence of chronic pain was associated with more depressive symptoms, more perceived stress, and poorer self-assessed health. In reviewing eight recent studies, Siddall and Loeser5
calculated that, when averaging across the studies, 65% of persons with SCI report having pain.
Many persons with SCI and chronic pain report that their pain is severe. For example, 25% of the sample in the study by Nepomuceno et al
reported their pain to be severe or extreme and 44% stated that it had increased over time. In the Siddall and Loeser review5
mentioned above, across all eight studies, an average of nearly one-third rated their pain as severe. The average pain intensity ratings provided by participants in a study by Widerstrom-Noga et al
was 5.6 on a 0–10 scale.
Pain in persons with SCI has been treated with a large number of biomedical and psychosocial interventions. However, the efficacy of these treatments has remained largely inconclusive and SCI-related pain has proven to be largely refractory to treatment. For example, Nepomuceno et al
reported that 38% of those with pain used medications to relieve the pain, but only 22% reported that they obtained consistent pain relief through the use of analgesics. Turner et al
found that less than half of their sample had ever used opioids for pain, even though opioids were the only treatment included on the checklist other than implanted morphine pump with an average perceived effectiveness rating greater than 3 out of a maximum of 5. Gabapentin was not included on the checklist, but was added by 14 respondents (4.6% of the 304 participants with pain; mean helpfulness = 3.21). Alternative treatments that were not included in the checklist, but were written in by the survey respondents, included massage (n
= 16, mean helpfulness = 3.63), acupuncture (n
= 11, mean helpfulness = 3.09), and marijuana (n
= 8, mean helpfulness = 4.38). The prevalence of use of these added treatments cannot be ascertained from these findings since it is possible that not everyone who had used them wrote them in.
More recent reviews of the evidence for pharmacological intervention for SCI neuropathic pain7,8
reveal a significant number of publications over the past 10 years suggesting efficacy for a variety of agents. The strongest evidence appears to exist for the use of pregabalin in a study by Siddall et al
On average, the group who received pregabalin reported a nearly two-point decrease in pain ratings on a 0–10 numeric rating scale, whereas the placebo group reported an average decrease of less than half a point. Furthermore, about 42% of patients who received pregabalin reported substantial (>30%) relief compared to only 16% for those on placebo.
Cranial electrotherapy stimulation (CES)
: CES is a non-traditional therapy involving the application of a small amount of current, usually less than 1 mA, through the head via ear clip electrodes. The analgesic action of subperception CES has been demonstrated in various anti-nociception models.10–12
Extracellular recording techniques indicated that CES modifies noxious evoked responses in pain-processing regions of the brains of rats.13,14
In humans, the mechanism of action of CES is not fully understood; however, it has been shown to ‘normalize’ neurotransmitter homeostasis,15
stimulate the hypothalamic–pituitary axis by increasing IGF-1 production (R. B. Smith and C. A. Ryser, ‘The use of CES in anti-aging medicine: Great things we learn when research goes wrong,’ presented at the International Oxidative Medicine Association meeting, Westminster, CO, 18 March 2000), bring neurotransmitters in stressed participants back to normal levels of homeostasis (M. S. Gold, A. L. Pottash, Sternbach, Barbaban, and Asunitto, ‘Anti-withdrawal effect of alpha methyl dopa and cranial electrotherapy,’ presented at the Society for Neuroscience meeting, Minneapolis, MN, 31 October 1982), and increase beta-endorphins in patients with chronic back pain.16
CES has been found to be effective in controlling anxiety, depression, insomnia, and generalized stress.17
A study by Capel et al
found that the intensity of pain of mixed types decreased significantly more in 15 participants with SCI who received active CES treatment twice a day for 2 hours for each of 4 consecutive days compared to 15 participants who received sham CES for the same amount of time. To further explore the use of CES in persons with SCI, we conducted a double-blind, sham-controlled, pilot study in 2002–2003 in which 38 veterans with SCI with neuropathic or musculoskeletal pain were randomly assigned to either CES (n
= 18) or sham CES (n
They were trained to self-administer the CES treatment at home and to complete pain ratings on a 0–10 scale immediately before and after each treatment session. The treatment group received 1 hour per day of 100 µA sub-sensation CES for a total of three consecutive weeks (21 days). The control group received sham CES for the same amount of time. After completion of the treatment, participants in the control group were offered an open-label use of the active device for 21 days. They again completed pain ratings before and after each daily session. The average change in pain on a scale from 0 to 10 from before to after each session
across the 21 days was −0.73 (SD = 1.15) points for the active CES treatment group and −0.08 (SD = 0.38) points for the sham treatment group. This was a significant difference (tseparate
= 2.27, P
< 0.05, Cohen's d
effect size = 0.76). Furthermore, 17 of the 20 participants from the group that originally had the sham treatment chose to participate in the subsequent open-label phase, and they reported a small but statistically significant pre- to post-session decrease in pain intensity (mean before = 5.97, mean after = 5.51, t
= 3.47, P
< 0.01). The participants in both groups also completed the Brief Pain Inventory (BPI) adapted for persons with disabilities20
before and after the 21-day treatment phase. The group who received the active CES treatment reported a significant decrease in pain interference (pre- and post-treatment BPI interference scores = 58.89 and 44.33 (SDs = 26.93 and 31.18, respectively); t
= 3.31, P
< 0.01). However, there was no significant change in pain interference for the group who received sham CES (pre- and post-BPI interferences scores = 53.10 and 48.40, respectively, (SDs = 27.88 and 28.03, respectively); t
= 1.22, P
> 0.20), a reduction of 4.7 points.
Building upon these pilot findings, a multisite study, funded by the Veterans Affairs Rehabilitation Research and Development Service, involving four Veterans Affairs medical facilities and one private rehabilitation center was conducted from 2004 to 2008. This paper reports the outcomes of that study. Approval of the study was obtained from the Institutional Review Board for Baylor College of Medicine and Affiliated Hospitals, the Office of the Institutional Review Board for Human Use at the University of Alabama at Birmingham, the Edward Hines, Jr. Veterans Affairs Hospital and North Chicago Veterans Affairs Medical Center Institutional Review Board, and the Louis Stokes Cleveland Veterans Affairs Medical Center Institutional Review Board.
The primary hypothesis of the study was that active CES will significantly reduce pain intensity more than sham CES from before to after the daily treatment sessions. The secondary hypotheses were that from before to after the 21-day trial: (1) active CES will significantly reduce pain intensity and pain interference as well as significantly impact pain quality, pain beliefs, and pain coping strategies more than sham CES and (2) active CES will significantly reduce health-related disability and psychological distress (depressive symptomatology, stress, and anxiety) more than sham CES.
The study was also designed to answer the following questions in secondary analyses: (1) what side effects, if any, will the participants in the active and sham CES conditions experience? and (2) what proportion of the participants will elect to participate in a long-term (6-month) open-label phase following initial short-term (21 days) use of active CES? For participants in the long-term component, we also wanted to determine: (1) how long and how frequently will they use the device during the 6-month phase and what problems will they encounter with the device? and (2) how satisfied will the participants be with CES and would they plan to continue to use CES if they could keep the device longer?