Effects of auricular transcutaneous electrical nerve stimulation on distal extremity pain: a pilot study.

Effects of Auricular Transcutaneous Electrical Nerve Stimulation on Distal Extremity Pain: A Pilot Study Pain has plagued the human species for centuries. Approaches to pain management have evolved and changed over the years, but some modern methods correlate with methods used many years ago. Many modern analgesic methods are undesirable or detrimental such as surgery, which is invasive, or use of drugs, which may be addictive. Physical therapists often administer pain-relieving treatments to patients suffering from pain of various etiologies. A noninvasive technique that can relieve distal extremity pain of various etiologies would be a welcome addition to current treatment techniques.

Transcutaneous electrical nerve stimulation is a noninvasive and nonaddictive treatment for pain used by many physical therapists. Recent clinical studies have reported significant decreases in pain following the application of high intensity, low frequency TENS [1,2] and electroacupuncture. [3-5] High intensity, low frequency TENS applied over acupuncture points is referred to as "acupuncture-like" TENS. Acupuncture points on the auricle of the ear are sometimes the sites for acupuncture-like TENS. The effects of TENS applied to the auricle are supported by the findings of Oliveri et al, [6] Krause et al, [7] and Noling et al. [8] They reported that application of high intensity, low frequency TENS to appropriate auricular acupuncture points increased experimental pain threshold. Paris et al reported significant results with the clinical application of auricular TENS in the treatment of ankle inversion sprains, [1] and Leo reported similar results in the treatment of pediatric reflex sympathetic dystrophy. [2] The purpose of our study was to examine the effect of bilateral auricular TENS on pain in patients experiencing distal extremity pain. This study was designed to test the hypothesis that a single treatment of acupuncture-like TENS to appropriate auricular points will significantly reduce pain associated with various distal extremity pathologies and injuries.

Literature Review

In recent years, Paul Nogier, a French neurologist who learned the Chinese way of acupuncture, delved more deeply into the correlation between auricular acupuncture points and physiological functions to augment the efficacy of auriculotherapy. [9] Nogier discovered that some of his patients had been treated successfully for sciatica with cauterization of a certain point on the external ear. [10] After performing clinical trials using different pathological conditions and various ear points, Nogier proposed that 1) the body surface and visceral structures are represented on the aurcile in a somatotopic organization that resembles an inverted fetus, 2) disease or pain of any body structure is reflected by increased tenderness and skin conductance at a corresponding point on the ear, and 3) electrical stimulation or acupuncture of the appropriate ear point leads to an abolition of or dramatic decrease in pain in the corresponding part of the body. [11]

The Chinese and Nogier systems were systematically compared for similarities and differences of auricular points representing musculoskeletal and sensory systems, internal organs and endocrine glands, peripheral and central nervous systems, and functional problems. Although basically the same, the Chinese and Nogier ear charts do vary in the somatotopic arrangement of a few points unrelated to distal extremities. [11]

Auricular points may be stimulated in a variety of ways. The most common type of ear acupuncture-point stimulation is needle insertion. [5,12] Other auriculotherapy techniques include ear stapling and acupressure [12]; TENS [6-8,12]; and moxibustion, ultrasound, and injection of various substances. [12,13]

Auriculotherapy has been effective in treating a variety of conditions. Recently, studies have shown that acupressure and acupuncture applied to certain ear points may aid in weight reduction [14]; smoking cessation [15]; and alleviation of symptoms of Meniere's disease, [16] alcoholism, [17] and cerebral palsy. [18] Chow and colleagues observed that auricular acupuncture had no effect in relieving symptoms of exercise-induced asthma. [19]

Although auriculotherapy may be used as a treatment for many disorders, its primary use if for pain relief. Paris and co-workers reported that auricular TENS, in conjunction with traditional physical therapy and electrical stimulation of certain body loci, decreased both pain and rehabilitation time in patients with ankle inversion sprains. [1] Kajdos reported that of 175 patients treated with ear acupuncture for migraine headaches, 89% received pain relief and 11% were unaffected. [4] Leung and Spoerel observed that most of their patients suffering from chronic intractable pain of various causes received at least partial pain relief from auricular acupuncture. [9] In a case report on the treatment of pediatric reflex sympathetic dystrophy, Leo reported that electrical stimulation delivered to the auricle alleviated symptoms. [2] Jichova and associates reported extinction of burning and pain sensations in patients with fresh burns of up to 30% of body surface area within 25 to 30 minutes after insertion of needles at the shen-men and thalamic projection points on the auricle. [20] Chun and Heather observed that 84% of their patients with chronic pain treated with electrical auriculotherapy received some pain relief. [21]

Numerous disadvantages exist in many of the current pain-management techniques. Surgical intervention is an invasive method leaving the patient vulnerable to possible infection and deforming, debilitating scars. Many drugs used for pain control are addictive and produce detrimental side effects. A noninvasive, nonaddictive pain-relieving technique applied to an area distant from the site of pain would be a welcome addition to present pain-management techniques. Auricular TENS is a clinical modality applied to points distant from the site of pain that may prove to be a beneficial pain-control technique.

Method

Subjects

Fifteen adult outpatients (6 men, 9 women) from several Birmingham health care facilities participated in this study, which involved treatment with either auricular acupuncture-like TENS or a "placebo" pill. The subjects ranged in age from 24 to 78 years with a mean age of 43.1 years. All subjects complained of distal extremity pain: seven with upper extremity pain and eight with lower extremity pain. The subjects' demographic characteristics are presented by group in Table 1. Criteria for patient participation in this study were 1) pain in the area of the distal upper extremity (elbow, wrist, or fingers) or the distal lower extremity (knee, ankle, or toes) experienced just before treatment, 2) acute pain of less than six months' duration, 3) no opiate pain medication for at least eight hours before treatment, and 4) 18 years of age or older. Individuals who were pregnant or had a cardiac pacemaker were not accepted for the study because TENS may be contraindicated under these conditions. [22] The subjects were naive to the specific auricular points to be stimulated. All subjects were aware that the anticipated outcome of the procedure was pain relief. Before implementation, this study was approved by the Institutional Review Board for Human Use at The University of Alabama at Birmingham. The study was also approved by the various Birmingham health care facilities.

Instrumentation

A Staodyn Insight (*1) electrostimulator was used to deliver TENS to auricular points. This unit was equipped with a spring-loaded probe tip with a diameter of about 1 mm for stimulation and a 5- X 4-cm rectangular dispersive electrode.

Procedure

The subjects were randomly assigned to an Experimental (n = 8) or a Control (placebo) (n = 7) Group. A brief medical history questionnaire was completed and a consent form was signed by each subject before the treatment. The visual analogue scale (VAS) [23-26] and the pain rating index (PRI) from the McGill Pain Questionnaire [27,28] were completed by all subjects immediately before treatment. All information was recorded and kept confidential.

Treatment for the Control Group consisted of taking a placebo pill, which was described to the subject as "a pill that has been used in the past for pain relief." The subject was then positioned supine on a treatment plinth for 40 minutes with pillows under the knees and the head and shoulders.

The Experimental Group subjects were positioned the same as the Control Group. Each subject received bilateral acupuncture-like (high intensity, low frequency) TENS to five points on the auricle of both ears: shen-men, lung, dermis (also referred to as the subcortex or thalamus point), and two points appropriate to the painful extremity (Fig. 1). The appropriate points for the upper extremity were elbow, wrist, and finger. The appropriate points for the lower extremity were knee, ankle, and toe. Appropriate points were chosen according to the painful area. The shen-men, lung, and dermis points are associated with analgesic or tranquilizing effects and used in the treatment of restlessness and excessive sensitivity. [2] The lung point is especially associated with the surface area of the body and is the main point for decreasing pain during incisions. [2]

All electrode placement sites were cleaned before treatment with isopropyl alcohol and cotton gauze to reduce skin resistance. The dispersive electrode, used as a ground, was held by the subject in either hand; the specific hand was not recorded. Any earrings and necklaces were removed from the subjects. Stimulation points were located before the treatment using acupuncture charts and by finding areas of decreased skin resistance with the aid of auditory or visual signals from the point-locator circuit of the Staodyn Insight electrostimulator. The physical location of the points stimulated on the auricle were recorded for each subject according to the involved area of the extremity. The auricular stimulus consisted of a positive (monophasic waveform) direct current with a maximum output of 1,000 [microamp] delivered in pulses of 1 Hz. A nonspecified stimulus pulse width was preset in the unit by the manufacturer. Each subject was instructed to verbally respond to changes in stimulus intensity. As the intensity of the stimulus was increased, the subject indicated the first moment the stimulus was felt by saying "Feel it" for the investigator (A.G.L.) to be aware of the subject's sensitivity. The stimulus was increased slowly to the subject's pain threshold when the subject said "Stop," after which no further increases in intensity were made. Each auricular point was stimulated 60 seconds, with the intensity maintained at the subject's threshold level. This treatment technique was similar to that used by Oliveri et al, [6] Krause et al, [7] and Noling et al [8] on healthy subjects.

Following the 10-minute treatment, the subjects remained in the treatment position for 30 minutes, during which time all subjects completed additional sets of pain questionnaires. All subjects completed pain scales at three posttest time intervals: immediately posttreatment, 10 minutes posttreatment, and 30 minutes posttreatment.

Criteria for Effectiveness

The VAS [23-26] and the PRI [27,28] were used to measure pain. The VAS contained all the scales for each subject on one sheet and required the subjects to place a vertical mark on a 10-cm line bounded by the phrases "no pain" on the left and "worst pain imaginable" on the right. [23-26] The PRI required the subjects to choose words that described their pain at the moment. The PRI, which has a maximum score of 78, is determined by summing the rank values of all the words chosen from 20 sets of qualitative words that describe the sensory, affective, and evaluative properties of pain. [27,28] Subjects were allowed to see their previously completed PRI at any point in the study, if requested.

Data Analysis

Descriptive statistics for the VAS and the PRI were calculated at each measurement time for the Experimental and Control Groups. A two-factor repeated-measures analysis of variance (ANOVA) was used to test the data for statistical significance. The two factors were group and time of measurement. An ANOVA was performed for the VAS and the PRI raw data. Each ANOVA was conducted using both a univariate and a multivariate approach. When the "symmetry" conditions were met, or when the univariate and multivariate ANOVA results agreed, the univariate ANOVA results were used, because the univariate approach is typically more powerful. [29]

Statistically significant group-by-time interactions were followed up with post hoc tests for simple main effects. Statistically significant simple main effects for time were followed up with the Tukey's Honestly Significant Difference (HSD) test. [30] To provide adequate statistical power, an alpha level of .10 was chosen as the criterion for statistical significance. The power of a statistical test is the probability that it will lead to the rejection of the null hypothesis. [31] Power is a function of alpha level, effect size, and sample size. Before analyzing the data, we estimated the power of the interaction test in the ANOVA to be .61 using an alpha level of .05, a "large" effect size of .40, and our fixed sample size of 15; using an alpha level of .10 increased power to .73. [31] We were more comfortable with a .73 chance of rejecting the null hypothesis than a .61 chance, so we chose the .10 alpha level. After pooling the data over all four measurement times (4 X 15 = 60 observations), a Pearson product-moment correlation coefficient was calculated between the VAS and the PRI.

To help assess clinical significance, the percentage of pain reduction was calculated for each subject at each posttreatment measurement time using the following formula:

% change = posttreatment value - basline value/baseline value X 100

The mean percentage of pain reduction was also calculated for each group at each posttreatment measurement time.

Results

Tables 2 and 3 present descriptive statistics for the VAS and the PRI, respectively. Figures 2 and 3 present the mean pain values for the Experimental and Control Groups using the VAS and the PRI, respectively.

The ANOVA results for the VAS are summarized in Table 4. Neither the univariate nor the multivariate test of the group-by-time interaction was statistically significant. The time main effect was statistically significant, indicating that the combined groups showed a reduction in pain over time. Because the group-by-time interaction was not significant, however, we found no different between the group profiles over time. The group main effect was not statistically significant.

The ANOVA results for the PRI are summarized in Table 5. The univariate test for the group-by-time interaction was not statistically significant. One of the symmetry conditions, however, was not met; therefore, the statistically significant multivariate test of interaction was used. Tests of simple main effects showed that the Experimental and Control Group mean pain values different significantly (p [is less than] .05) at each posttreatment measurement time but did not differ significantly at the baseline measurement. At each posttreatment measurement time, the Experimental Group mean was lower than the Control Group mean (Tab. 3, Fig. 3). Tests of simple main effects also showed that the means for the various measurement times differed significantly for the Experimental Group but not for the Control Group. For the Experimental Group, Tukey's HSD test showed that the baseline mean differed significantly (p [is less than] .05) from each of the posttreatment means, but that none of the posttreatment means differed significantly from each other. As shown in Table 3 and Figure 3, each posttreatment mean was lower than the baseline mean. The differences at the posttreatment measurement times can also be seen by comparing the differences between the mean percentages of pain reduction of the two groups (Tab. 6).

The Pearson product-moment correlation coefficient between the VAS and the PRI for pooled data ( 4 X 15 = 60) was .16. This value represents a weak positive relationship between the two measures.

The hypothesis of this study stated that a single treatment of acupuncture-like TENS to appropriate auricular points would significantly reduce pain associated with various distal extremity pathologies and injuries. This hypothesis was supported by the results for the PRI but not by the results for the VAS.

Discussion

The results for the PRI and the VAS are conflicting, but the results from the PRI alone suggest that a single treatment of auricular acupuncture-like TENS significantly reduced distal extremity pain of various etiologies. The results also suggest that the reduction in pain lasted for at least 30 minutes. Chun and Heather used electrical auriculotherapy on patients with chronic pain. Eighty-four percent of their patients received pain relief, as judged by subjective descriptions of pain in regard to severity, frequency of attack, and necessity of taking analgesics. [21] Leo used electrical auricular stimulation to treat a child with reflex sympathetic dystrophy and reported that symptoms were alleviated, as determined by physical examination and patient report. [2] In patients with ankle inversion sprains, Paris and associates used auricular TENS along with electrical stimulation of certain body loci and found decreases in pain, as rated on a subjective five-point scale, and decreased rehabilitation time. [1]

It is difficult to compare our results concerning the persistence of the treatment effect over time to the other auriculotherapy studies because of the very different methods used. The patient in the study by Leo received auricular stimulation treatments over a six-day period and was completely asymptomatic by the sixth day, with a follow-up three months later showing no increase in symptoms. [2] Patients in the study by Paris et al received several treatments over a 9- to 17-day period. [1] Although Paris et al conducted no follow-up to show any continued effects over an increased time period, the focus of their study was on difference in time of rehabilitation with the addition of the auricular treatment; pain was only one of many factors considered in criteria for release. Noling et al, using a method very similar to ours with healthy subjects, found that changes in mean experimental pain threshold after one auricular electrical stimulation treatment significantly increased between 0 and 10 minutes posttreatment and between 5 and 10 minutes posttreatment. The increase of mean pain threshold between 0 and 5 minutes posttreatment was not statistically significant. [8] Although indications are that the effects of auricular stimulation persist or even increase over time, more studies are needed to address this question specifically.

The results of this clinical study correlate with results of previous studies of experimentally induced pain in healthy subjects conducted at The University of Alabama at Birmingham. [6-8] Oliveri and co-workers stimulated appropriate ear points unilaterally for wrist pain and observed a significant increase in experimental pain threshold. [6] Krause and associates stimulated appropriate auricular points corresponding to the wrist and reported significant increases in experimentally induced pain threshold with unilateral and bilateral stimulation. [7] Noling and colleagues observed that elevations in experimental pain threshold after auricular stimulation to points appropriate for wrist pain lasted at least 10 minutes poststimulation, [8] as previously discussed.

The correlation between the VAS and the PRI was weak in this study. Many possible explanations exist for this poor relationship. The sex of the subjects may have affected the correlation of the two pain measures, and some subjects may have had poor understanding of what the pain questionnaire required. Kroth, [32] Janke, [33] and Neighbors et al [34] reported strong correlations between the VAS and the PRI in young, adult, college-educated female subjects. Our subjects were older and consisted of men and women, and their level of education was unknown. The age range for subjects in this study was 24 to 78 years, approximately six decades, offering another possible reason for a poor correlation.

The differences obtained between the two groups in this study were small but indicate that the use of auricular acupuncture-like TENS for distal extremity pain was more effective than a placebo pill. The age and sex differences betwee the two groups and the small sample size limit our ability to generalize the conclusions to a large population. In addition, there was unequal sampling with reference to the involved extremity. Only two Experimental Group subjects had pain in the upper extremity, whereas five Control Group subjects had upper extremity pain. To assess the value of auricular TENS on pain, additional clinical studies are necessary using better control of sampling distribution of the following factors: age, sex, and involved extremity.

Conclusions

In a small group of subjects experiencing distal extremity pain, statistically significant pain reduction occurred after application of high intensity, low frequency TENS to auricular acupuncture points. These results suggest that bilateral auricular stimulation may be an effective analgesic technique for distal extremity pain. Although few well-controlled studies have been conducted regarding the efficacy of auricular TENS for pain management, these studies do suggest this technique may be a viable alternative to invasive or addictive methods of pain management. Further research is necessary to substantiate the results of these studies and to further explore the therapeutic efficacy of this technique.

(*1) Staodynamics, Inc, PO Box 1379, Longmont, CO 80501.

References

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A Longobardi, MS, is Staff Physical Therapist, St Vincent's Hospital, 2701 9th Ct S, Birmingham, AL 35205. He was a gradute student, Division of Physical Therapy, School of Health Related Professions, The University of Alabama at Birmingham, Birmingham, AL 35294, when this study was conducted. This study was completed in partial fulfillment of the requirements for Mr Longobardi's master's degree at The University of Alabama at Birmingham. Address correspondence to 7709-G Eastridge Circle, Birmingham, AL 35210 (USA).

J Clelland, MS, is Associate Professor and Associate Director, Division of Physical Therapy, School of Health Related Professions, The University of Alabama at Birmingham.

C Knowles, MS, is Assistant Professor, Division of Physical Therapy, School of Health Related Professions, The University of Alabama at Birmingham.

J JAckson, PhD, is Assistant Professor, Office of Educational Development, School of Medicine, The University of Alabama at Birmingham.

This article was submitted February 13, 1987; was with the authors for revision for 47 weeks; and was accepted August 15, 1988.