Publications
APS Bulletin • Volume 9, Number 2, March/April 1999
Article
Percutaneous Electrical Nerve Stimulation (PENS): A Promising Alternative-Medicine Approach to Pain Management
Paul F. White, MD PhD; Jennifer Phillips, BS; Timothy J. Proctor, BA; William F. Craig, MD
EDITOR'S NOTE: Former Research Update Department Editor Robert J. Gatchel, PhD, submitted the following article. We thank Dr. Gatchel for his contribution to the Bulletin.
In the March/April 1998 issue of APS Bulletin, Berman and Swyers reviewed the increase in the application of alternative-medicine approaches to managing chronic pain syndromes. Such approaches are also being taken with other medical conditions. Indeed, the Journal of the American Medical Association dedicated its entire November 18, 1998, issue to alternative medicine. Moreover, the Office of Alternative Medicine at the National Institutes of Health (NIH) has just become the National Center for Complementary and Alternative Medicine, with a projected budget of approximately $50 million. Such events signal that complementary and alternative-medicine approaches are now in the mainstream of medicine in this country.
In the same issue of the Bulletin, Wilentz (1998) summarized an NIH consensus development conference on one type of alternative medicine—acupuncture. This conference concluded, "...there is strong evidence that needle acupuncture therapy is effective for the treatment for postoperative nausea and vomiting, postoperative dental pain, and nausea and vomiting associated with chemotherapy and pregnancy... Acupuncture may be an effective therapy for addiction, stroke rehabilitation, headache, menstrual cramps, tennis elbow, fibromyalgia, low-back pain, carpal tunnel syndrome, and asthma, but in these cases, the scientific data supporting the procedure's effectiveness are less convincing" (Wilentz, p.1).
Indeed, it is possible that a direct relationship between peripheral nerves and acupuncture points exists (Lewith, Kenyon, & Lewis, 1996). In addition, it has been suggested that the analgesic effect provided by acupuncture is mediated by the endogenous opioid system and biogenic amines, such as gamma-amino butyric acid (GABA), serotonin, and norepinephrine (Kiser et al., 1983). An extension of traditional acupuncture has been to add electrical stimulation to the acupuncture needles (this is so-called electroacupuncture). This technique differs from traditional acupuncture in that the needle itself is not the main focus of treatment. Instead, it serves as a conductor of electricity used to decrease pain. This technique has been investigated as a form of afferent stimulation since the 1970s.
Percutaneous electrical nerve stimulation
During the past few years, the efficacy of a novel complementary and alternative-medicine procedure, known as percutaneous electrical nerve stimulation (PENS), has been investigated for the management of acute and chronic pain syndromes. PENS is a new analgesic therapy that combines the advantages of both electroacupuncture and transcutaneous electrical nerve stimulation (TENS). PENS therapy utilizes acupuncture-like needle probes positioned in the soft tissues to stimulate peripheral sensory nerves at the dermatomal levels corresponding to the local pathology. TENS, in contrast, is a procedure that involves electrical stimulation of cutaneous electrode pads placed in a standard dermatomal pattern. PENS is preferable to TENS in that it bypasses the resistance of the cutaneous barrier and delivers the electrical stimulus in closer proximity to the nerve endings located in the soft tissue, muscle, and periostium of the involved dermatomes. In patients with cancer pain secondary to bony metastases, electrical stimulation of the nerve endings located in the periostium is an important factor in achieving PENS-induced analgesia (Ahmed, Craig, White, & Huber, 1998). Compared with dorsal column stimulation, the PENS technique is less invasive, less costly, and less risk-ridden. Moreover, PENS is a useful, nonpharmacological supplement to opioid and nonopioid analgesic medications that avoids the problem of tolerance and physical dependence that is associated with long-term opioid use. The excessive sedation and gastrointestinal side effects that are often experienced with conventional analgesics are also avoided with PENS therapy (Ahmed, Craig, White, & Huber).
Recent research evidence of the treatment efficacy of PENS
PENS therapy has been found to be effective in the management of pain associated with a number of medical conditions, including acute herpes zoster (Ahmed, Craig, White, Ghoname et al., 1998), cancer pain secondary to bony metastases (Ahmed, Craig, White, & Huber, 1998), the prevention and treatment of migraine headaches after electroconvulsive therapy (Ghoname, Craig, & White, in press), and the management of low-back pain (Ghoname, Craig, White, Ahmed, et al., in press) and sciatica (Ghoname et al., in press). For example, the investigation by Ahmed, Craig, White, Ghoname et al. that examined the usefulness of the PENS technique with acute herpes zoster found that PENS compared favorably with standard antiviral drug therapy (i.e., acyclovir) with respect to the severity of dermatomal pain, impact on sleep and physical activity, resolution of skin lesions, and incidence and severity of postherpetic neuralgia (PHN). Fifty immunocompetent adults with recent acute onset of herpes zoster lesions were randomly assigned to receive either PENS or antiviral therapy. The PENS group experienced comparable healing of their lesions, consistently lower pain scores, and improvement in physical activity and quality of sleep, as measured by Visual Analog Scales (VAS). In addition, of the patients experiencing PHN symptoms, those receiving PENS noted a greater decrease in the associated pain at 3 and 6 months after the acute illness. This study indicated that the PENS technique may be an acceptable alternative treatment for acute herpes zoster lesions, and that it compared favorably with traditional antiviral drug treatment.
In the study by Ahmed, Craig, White, and Huber (1998) evaluating the role of PENS in the management of cancer pain secondary to bony metastases, the investigators examined the effectiveness of PENS in the short-term management of pain in three patients with metastatic cancer whose symptoms were not adequately controlled with traditional opioid and nonopioid analgesics. In two (those with bony metastases) of the three patients described, the PENS procedure provided short-term analgesic-sparing effects, as well as significant acute pain relief. However, in the patient without bony metastases, PENS was ineffective in providing clinically significant pain relief. This study suggests that the use of the PENS procedure may help decrease the need for analgesic drugs and might offer an alternative to escalating doses of analgesics for patients with pain secondary to bony metastases. Of course, additional research with a larger sample size is needed in this area.
An investigation examining the use of PENS in the treatment of headache pain after electroconvulsive therapy (ECT) suggests yet another situation in which this technique can be used as an alternative to opioid analgesics (Ghoname, Craig, & White, in press). The authors describe five patients for whom PENS was an effective alternative to opioid analgesics in treating ECT-evoked migraine-type headache pain. Again, a larger sample-size study is needed to define the role of PENS in the management of migraine headaches.
The study by Ghoname, Craig, White, Ahmed, Hamza, and Noe (in press) evaluating the use of PENS in the management of sciatica found that this technique proved to be more effective in the short-term management of sciatic pain than standard TENS treatment. It was also found to be more effective than TENS in improving physical activity and quality of sleep. Sixty-four adults with sciatica related to lumbar disc herniation were randomly assigned to three treatment groups (namely, sham PENS, PENS, and TENS). All patients were treated for a period of 30 minutes, three times per week for 3 weeks. Although both the PENS and TENS techniques more effectively decreased sciatic pain than the sham PENS, as determined by VAS scores, the PENS technique was judged by the PENS patients to be more effective (42% versus 23% for the TENS). In addition, the decrease in the need for analgesic medication when using PENS also suggested that the PENS therapy was the more effective of the two treatments overall. The PENS technique was also significantly more effective than the TENS and sham treatments in improving quality of sleep and physical activity, as measured by the VAS and the Health Status Survey Short Form (the SF-36). Seventy-three percent of the PENS patients reported that PENS was the most desirable treatment, and 71% of patients indicated that they would be willing to pay out of pocket for this treatment. The authors concluded that the PENS procedure was more effective than TENS in providing short-term pain relief and improved functionality in patients with sciatica.
In a recently completed study evaluating the therapeutic effectiveness of PENS in patients with low-back pain (LBP), it was found to be highly effective in the short-term management of this patient population (Ghoname, Craig, White, Ahmed, Hamza, Henderson, et al., in press). LBP contributes to significant disability and lost wages each year in the United States. The currently used opioid and nonopioid analgesic drugs produce side effects and are of limited benefit in the long-term management of this patient population, however. Patients are increasingly turning to short-term nonpharmacological alternatives like PENS. The current study was designed to compare the relative effectiveness of PENS, TENS, and low-back exercise therapy using a sham-controlled crossover study design in patients with LBP.
In the LBP study, 60 patients with LBP secondary to degenerative disc disease were treated with four different therapeutic modalities: PENS, sham PENS, TENS, and spine exercise over a 16-week study period. All patients had been maintained on a stable oral analgesic treatment regimen for at least 3 months prior to entering the study. The basic PENS therapy consisted of the placement of 10 (ten) 32-gauge stainless-steel acupuncture-like needle probes into the soft tissue in the low-back region to a depth of 2-4 cm. The probes were connected to a low-output (5 mAmp) battery-powered electrical generator and initially stimulated at a frequency of 4 Hz. The sham PENS therapy consisted of needle probes placed in the same pattern as PENS, except no electrical stimulation was applied. The locations of the needle probes for the PENS and sham PENS treatments are illustrated in Figure 1. The standard TENS therapy consisted of the placement of four medium-sized (2.5 cm) cutaneous electrode pads in a standard dermatomal pattern. These electrodes were also stimulated at a frequency of 4 Hz, with a pulse duration of 0.1 second. The low-back exercise therapy consisted of spine flexion while patients were seated on a chair with full abduction of both hips. The patients were instructed to slowly touch the floor with both hands while remaining seated; this was followed by full extension. The maneuver was repeated a minimum of 30 times during each treatment session.
FIGURE 1. The Locations of Needles for the Sham PENS and PENS Treatments.
NOTE. With PENS therapy, each of the five bipolar electrical stimulating leads is connected to a pair of needles, alternating the positive (+) and negative (-) positions as shown in the illustration. |
Each of the above treatments was administered for a period of 30 minutes three times per week for 3 weeks. The pretreatment assessments included the SF-36, as well as the VAS for pain, physical activity, and quality of sleep, with scores ranging from 0-10 (where 0 = the best and 10 = the worst). Patients rated their pain on the VAS after each treatment session. At the end of each 3-week treatment period, the SF-36 was repeated. After the patients had received all four treatment modalities, a global (overall) assessment questionnaire was completed.
The results of this study clearly demonstrated that PENS was significantly more effective in decreasing pain VAS scores after each treatment than the sham PENS, TENS, and low-back exercise therapies. Also, the daily oral analgesic requirement was more significantly reduced with PENS (50%) compared with sham PENS (4%), TENS (15%), and low-back exercise (0). In the overall assessment, 91% of the PENS patients reported that PENS was the most effective pain-relieving modality utilized. PENS was also significantly more effective than the other three modalities in improving physical activity, quality of sleep, and the sense of patients' well-being. The SF-36 evaluations also confirmed the superiority of PENS relative to the other treatment modalities with respect to posttreatment functionality. Finally, 81% of the patients stated that they would be willing to pay out of pocket to receive PENS therapy, whereas only 4%-9% would be willing to do so for the other three treatment modalities. It was concluded that PENS therapy was more effective than conventional TENS and exercise therapy in improving short-term outcomes in patients with LBP. Current studies are being conducted to examine the cost-effectiveness and cost-benefit of PENS therapy as a supplement to conventional oral analgesic medication and exercise programs on long-term patient outcome measures such as return to work, healthcare utilization, and patient satisfaction.
Conclusion
The PENS research program we have reviewed addresses one of the key issues that the NIH Consensus Panel on Acupuncture noted in its report, namely, that further research on acupuncture and related therapies should use study designs that can withstand rigorous scientific scrutiny. As evidenced by the initial results summarized here, the PENS technique is a form of acupuncture therapy that is currently being evaluated by using scientifically valid methodology. Results to date indicate that this procedure can be an effective alternative method of pain management for a wide variety of acute and chronic pain conditions. In the future, the PENS procedure will have to be evaluated in the long-term management of other types of pain conditions in order to more rigorously and unequivocally document its efficacy as a pain management technique.
References
Ahmed, H.E., Craig, W.F., White, P.F., Ghoname, E.A., Hamza, M.A., Gajraj, N.M., & Taylor, S.M. (1998). Percutaneous electrical nerve stimulation: An alternative to antiviral drugs for acute herpes zoster. Anesthesia and Analgesia, 87(1), 1-4.
Ahmed, H.E., Craig, W.F., White, P.F., & Huber, P. (1998). Percutaneous electrical nerve stimulation (PENS): A complementary therapy for the management of pain secondary to bone metastasis. The Clinical Journal of Pain, 14, 320-323.
Berman, B.M., & Swyers, J.P. (1998). Applying alternative medical approaches to managing chronic pain syndromes: If not now, when? APS Bulletin, 8(2), 4-6.
Ghoname, E.A., Craig, W.F., & White, P.F. (in press). Percutaneous electrical nerve stimulation (PENS): An alternative to opioid analgesics for treating headache pain after electroconvulsive therapy. Headache.
Ghoname, E.A., Craig, W.F., White, P.F., Ahmed, H.E., Hamza, M.A., Henderson, B.N., Gajraj, N.M., Huber, P.J., & Gatchel, R.J. (in press). Percutaneous electrical nerve stimulation: A novel therapy for the short-term management of low back pain. Journal of the American Medical Association.
Ghoname, E.A., Craig, W.F., White, P.F., Ahmed, H.E., Hamza, M.A., & Noe, C.E. (in press.) Percutaneous electrical nerve stimulation: An alternative to TENS in the management of sciatica. Anesthesiology.
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Paul F. White is professor and Eugene McDermott chair of anesthesiology and pain management, Jennifer Phillips and Timothy J. Proctor are PhD candidates in the department of psychiatry (psychology division), and William F. Craig is clinical professor in the department of anesthesiology and pain management at the University of Texas Southwestern Medical Center at Dallas.