Auriculotherapy for Pain Management: A Systematic Review ...

Auriculotherapy for Pain Management:A Systematic Review and Meta-Analysis

of Randomized Controlled Trials

Gary N. Asher, MD, MPH,1,2 Daniel E. Jonas, MD, MPH,3 Remy R. Coeytaux, MD, PhD,4

Aimee C. Reilly, LAc,1 Yen L. Loh, MD,1 Alison A. Motsinger-Reif, PhD,5 and Stacey J. Winham, MS5

Abstract

Objectives: Side-effects of standard pain medications can limit their use. Therefore, nonpharmacologic pain relieftechniques such as auriculotherapy may play an important role in pain management. Our aim was to conduct asystematic review and meta-analysis of studies evaluating auriculotherapy for pain management.Design: MEDLINE,� ISI Web of Science, CINAHL, AMED, and Cochrane Library were searched throughDecember 2008. Randomized trials comparing auriculotherapy to sham, placebo, or standard-of-care control wereincluded that measured outcomes of pain or medication use and were published in English. Two (2) reviewersindependently assessed trial eligibility, quality, and abstracted data to a standardized form. Standardized meandifferences (SMD) were calculated for studies using a pain score or analgesic requirement as a primary outcome.Results: Seventeen (17) studies met inclusion criteria (8 perioperative, 4 acute, and 5 chronic pain). Aur-iculotherapy was superior to controls for studies evaluating pain intensity (SMD, 1.56 [95% confidence interval(CI): 0.85, 2.26]; 8 studies). For perioperative pain, auriculotherapy reduced analgesic use (SMD, 0.54 [95% CI:0.30, 0.77]; 5 studies). For acute pain and chronic pain, auriculotherapy reduced pain intensity (SMD for acutepain, 1.35 [95% CI: 0.08, 2.64], 2 studies; SMD for chronic pain, 1.84 [95% CI: 0.60, 3.07], 5 studies). Removal ofpoor quality studies did not alter the conclusions. Significant heterogeneity existed among studies of acute andchronic pain, but not perioperative pain.Conclusions: Auriculotherapy may be effective for the treatment of a variety of types of pain, especially post-operative pain. However, a more accurate estimate of the effect will require further large, well-designed trials.

Introduction

Pain affects more Americans than diabetes, heart dis-ease, and cancer combined,1 and accounts for more than

20% of medical visits and 10% of prescription drug sales.2 Oneof the most common approaches to managing pain relief,the World Health Organization analgesic ladder,3 details theuse of both opioid and nonopioid medications in a stepwisefashion. However, up to 80% of patients receiving opioidmedications experience at least one adverse event, mostcommonly constipation (41%), nausea (32%), or somnolence(29%); the number needed to harm for these common events is

between three and five.4 Additionally, gastrointestinal toxic-ity related to the use of nonsteroidal anti-inflammatory drugs(NSAID) is estimated to cause more than 100,000 hospitali-zations and over 16,000 deaths annually in the United States.5

Cardiovascular risk is also elevated with use of mostNSAIDs.6 For these reasons, methods of nonpharmacologicpain relief, such as acupuncture, mind–body interventions,and manipulative therapies, have been advocated as adjunctsto pharmacologic therapy.7–9

Acupuncture has been shown to be effective for pain reliefdue to a variety of causes including low back pain,10,11 oste-oarthritis,12 and headache.13 Auriculotherapy is an adjunct to

1Department of Family Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC.2Program on Integrative Medicine, Department of Physical Medicine and Rehabilitation, University of North Carolina at Chapel Hill,

Chapel Hill, NC.3Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC.4Department of Community and Family Medicine, Duke University, Durham, NC.5Department of Statistics, North Carolina State University, Raleigh, NC.

THE JOURNAL OF ALTERNATIVE AND COMPLEMENTARY MEDICINEVolume 16, Number 10, 2010, pp. 1097–1108ª Mary Ann Liebert, Inc.DOI: 10.1089/acm.2009.0451

1097

traditional acupuncture and over the last 60 years has devel-oped into a distinct treatment system of its own. It is based ona set of anatomical maps superimposed onto the ear. Stimu-lating a point on the map is proposed to affect the grossanatomical organ associated with that point. For the ear, au-ricular points may be stimulated with needles (auricularacupuncture); Vaccaria seeds, probes, or fingers (acupressure);electrical units attached to auricular needles (percutaneouselectrical nerve stimulation) or directly to the skin (TENS—transdermal electrical nerve stimulation or auricular electro-acupuncture); or laser; all of which may be considered formsof auriculotherapy.

Early studies of auriculotherapy have demonstrated bene-ficial effects on both pain and anxiety including pain associ-ated with cancer,14 knee arthroscopy,15 and hip fracture andhip arthroplasty.16 Several recent small studies have sug-gested that auricular acupuncture alone can relieve pain andanxiety in the prehospital transport phase of hip fracture16,17

and reduce acute pain due to a variety of causes in theemergency department setting.18 Recently, a systematic re-view of auriculotherapy for perioperative pain concluded thatthe evidence for efficacy was ‘‘promising but not compel-ling.’’19 However, because auriculotherapy is currently usedin a wide range of acute and chronic pain conditions beyondthe perioperative period, it is important to assess its clinicalutility in general. Therefore, in this review our primary ob-jective was to conduct a systematic review and meta-analysisof the efficacy of auriculotherapy for all types of pain. Wepresent these data as a whole and also by category of pain(perioperative, acute, and chronic).

Materials and Methods

Data sources and searches

We searched MEDLINE,� Cochrane Database of Systema-tic Reviews, Cochrane Central Register of Controlled Trials,AMED, ISI Web of Science, and CINAHL from inceptionthrough December 2008, using the following terms: ‘‘auricularacupuncture,’’ ‘‘ear acupuncture,’’ and ‘‘auriculotherapy.’’ Welimited the electronic searches to human subjects and, due toresource constraints, English language. We attempted toidentify additional studies through hand searches of referencelists, as well as our own files. All citations were imported intoan electronic database (Endnote v. X1).

Study selection

Trials were included if they (1) were randomized; (2)compared auriculotherapy to sham auriculotherapy control,standard medical care, or waiting-list control; (3) measuredthe effect on pain or medication use; (4) and were published inEnglish in a peer-reviewed journal. We chose to excludestudies that compared auriculotherapy to a nonauricul-otherapy active control treatment that did not have clearevidence of efficacy. Two (2) reviewers independently as-sessed titles and abstracts, which were excluded only if bothreviewers agreed that the trial did not meet eligibility criteria.Full-text articles of remaining citations were retrieved andassessed for inclusion by 2 reviewers. Disagreements wereresolved by consensus. Results published only in abstractform were not included unless adequate details were avail-able for quality assessment.

Data abstraction and quality (internal validity)assessment

We designed and used a structured data abstraction form.Trained reviewers abstracted data from each study and as-signed an initial quality rating. A second reviewer read eachabstracted article, evaluated the completeness of the dataabstraction, and confirmed the quality rating. Differences inquality ratings were resolved by discussion or by involving athird senior reviewer. The following data were extracted:study design, setting, population characteristics (includingage, sex, and race), inclusion and exclusion criteria, inter-ventions, comparisons, additional medications or interven-tions allowed, outcome assessments, attrition, withdrawalsattributed to adverse events, results, and adverse events re-ported. We recorded intention-to-treat results if available.

For the auriculotherapy interventions, we abstracted de-tails based on the STRICTA (Standards for Reporting Inter-ventions in Controlled Trials of Acupuncture) criteria for thereporting of acupuncture trials,20 including point selectionmethod, point locations, number of points per ear, needletype, use of electrical or laser stimulation, number of treat-ments, treatment frequency, and duration of each treatment.We also abstracted data on the practitioner type, years ofexperience, and acupuncture style. For the control interven-tion, we abstracted similar details. The country of the studywas also recorded.

We assessed the quality of trials based on the criteria of theU.S. Preventive Services Task Force and the National HealthService Centre for Reviews and Dissemination (U.K.).21,22

Quality assessment elements included randomization meth-od, allocation concealment, and blinding; similarity of com-pared groups at baseline; maintenance of comparablegroups; reporting of dropouts, crossover, adherence, andcontamination; overall and differential loss to follow-up; andintention-to-treat analysis. Attrition was defined as thenumber of randomized subjects who did not reach the studyendpoint.23

Trials that met all criteria were rated ‘‘good quality,’’ whilethose that failed to meet combinations of items were rated‘‘poor quality.’’ The remainder received a quality rating of‘‘fair.’’ This includes studies that presumably fulfilled allquality criteria but did not report their methodologies to anextent that answered all of our questions. As the fair-qualitycategory is broad, studies with this rating vary in theirstrengths and weaknesses. A poor-quality trial is not likely tobe valid—the results are at least as likely to reflect flaws in thestudy design as the true difference between the interventionand control.

Data synthesis and analysis

We summarized the overall strength of evidence for theefficacy of auriculotherapy for each set of pain indications intoevidence profiles. The overall strength of evidence for a par-ticular key question reflects the design, quality, consistency,and magnitude of effect of the set of studies relevant to thequestion. We rated the overall strength of evidence as low,moderate, high, or insufficient using an approach establishedby the Agency for Healthcare Research and Quality Evidence-Based Practice Centers.24 High strength of evidence indicateshigh confidence in the estimate of effect and that the evidencereflects the true effect; further research is unlikely to change

1098 ASHER ET AL.

our confidence. Moderate strength of evidence indicatesmoderate confidence, and further research may change ourconfidence in the estimate as well as the estimate itself. Lowstrength of evidence indicates low confidence in the estimateand further research is likely to change our confidence inthe estimate and is likely to change the estimate. Insufficientindicates that evidence is unavailable or does not permit es-timation of an effect.

Standardized mean differences (SMD) and 95% confidenceintervals (CI) were calculated for all comparisons. A stan-dardized mean difference refers to the raw difference in thesample treatment mean and the sample control mean dividedby the pooled standard deviation of both the treatment andcontrol groups. Because the times to study endpoints greatlyvaried among the studies, weighted mean differences werenot calculated. The use of the pooled standard deviation in theSMD accounts for the inconsistent study endpoints by placingthe treatment differences on the same comparable scale. SMDstherefore are not interpreted on the original scale, but areinterpreted in terms of number of standard deviations. Forexample, an SMD of 3.0 would mean that the treatment meanis approximately 3.0 standard deviations higher than thecontrol mean. Mean differences around 0.2 are often consid-ered small while those �0.8 are considered large.25 For ex-ample, a mean difference of 0.5 indicates that the mean of thetreated group is at the 69th percentile of the comparisongroup—a moderate effect—while a difference of 1.5 indicatesthat the mean of the treated group is at the 93% of the com-parison group—a large effect.

Study comparisons based on pain scales compared thestandardized difference in mean decrease in pain from base-line (to end of study) between the treatment and controlgroup. The numerical rating scale (NRS) was converted to a100-point scale for comparisons with the 100-point visualanalogue scale (VAS). Study comparisons based on painmedication use compared the percentage decrease in painmedication use between treatment and control groups. Wetested whether these decreases, in either pain scale or painmedication use, were significantly different from zero acrossstudies. For the overall meta-analysis comparing acupunctureto a control, only the studies that utilized a pain scale measurewere included because of concerns of comparability betweenthe pain scale and analgesic use outcomes. For all compari-sons, an SMD of zero indicates no difference between groups.

Study results were combined using the two-tailed p-valuesreported from each individual study. If a p-value was notreported, it was calculated from the reported standard error.Because study sample sizes and variances were not constant,reported differences were converted to standardized meandifferences; studies were weighted by the inverse of the studyvariance so that studies with lower variance received moreweight. A formal hypothesis test for heterogeneity was per-formed using Cochran’s Q statistic.26 As an alternative to Q,the inconsistency index I2 is reported,27 as well as t2,28 thebetween-study variance. Results for both random and fixed-effects models were calculated, but because significant het-erogeneity among studies was often found, we report theresults from random effects models only.29 To further inves-tigate heterogeneity, studies that employed multiple controlgroups14,30,31 were compared using the control group with theleast active intervention, and studies that used an activecontrol known to be efficacious for pain were excluded.32,33

Analysis was performed using the software package Com-prehensive Meta Analysis (www.meta-analysis.com).

Subgroup analyses were performed for perioperativestudies reporting pain medication use, studies of acute pain,and studies of chronic pain. Although other subgroups maybe important to consider, too few studies were available forsuch analyses.

Forest plots and funnel plots were created for the overallresults and for each subgroup analysis. Sensitivity analysiswas performed by removing each study and recalculatingthe overall results of the analysis. Cumulative analysis wasperformed to assess the possible treatment effect over time.Comparisons were performed with and without poor qualitystudies to assess the effect of study quality. This study wasapproved by the University of North Carolina institutionalreview board.

Results

Our search revealed 554 citations, of which 133 full-textarticles were reviewed. A total of 17 studies (1009 subjects) metour inclusion criteria (Fig. 1) and were included in the review.Attempts were made to contact the authors of an additionalthree publications that may have been eligible for inclusion butwere not because no replies were elicited.34–36 For 5 of the17 included studies, additional data were obtained from theauthors to enable inclusion in the meta-analysis.30–33,37 Four(4) studies included in the review were excluded from themeta-analysis due to incomplete data.17,38–40

The 17 included studies encompassed a wide variety ofauriculotherapy interventions (Table 1) including auricularneedles that were placed and removed after a single session(two studies); indwelling auricular needles that could remainin place for up to 30 days (six studies); electrical stimulation ofeither indwelling auricular needles (five studies) or transcu-taneously without needles (two studies); laser stimulation(one study); and acupressure (one study). Most studies usedeither a VAS (10/17) or measures of the amount of painmedication use (5/17) as a primary outcome measure. Theremaining studies used other measures, including a NRS andreports of ‘‘pain relief’’ or ‘‘pain decrease.’’

Thirty-five percent (6/17) of trials were rated as goodquality, 24% (4/17) were fair quality, and 41% (7/17) werepoor quality (see Appendix). Selection of auricular acupointswere varied among the studies based on the type and loca-tion of pain being treated; however, shenmen was the mostcommonly included point (10 studies) followed by thalamus(4). Visual inspection of the funnel plots for each comparisondid not indicate substantial publication bias. Table 1 liststype of intervention and control treatments, primary out-come measures, and acupoints for each study.

All pain types

Overall, 12 studies reported primary outcome effects infavor of auriculotherapy, 3 studies found mixed results (dif-ferent direction of outcomes for multiple outcome scales ormultiple times of outcome measurement), and 2 studies re-ported no difference between auriculotherapy and controlinterventions (Table 1). Of the 17 studies included in our re-view, 8 reported sufficient data for change in pain intensity tobe included in an overall meta-analysis; 3 studies that didreport on pain intensity did not provide enough data to be

AURICULOTHERAPY FOR PAIN 1099

included in the meta-analysis.17,39,40 Auriculotherapy inter-ventions for studies incorporated into the meta-analysis in-cluded auricular acupuncture with and without electricalstimulation, TENS, and laser auriculotherapy; control grouptreatments included sham auriculotherapy, placebo pill, andstandard medical care. Auriculotherapy was significantlymore effective than control procedures at decreasing painintensity as measured by VAS or NRS (SMD 1.56; 95% CI:0.85, 2.26; eight studies) (Fig. 2A). Though significant het-erogeneity existed among the studies (Q-value¼ 58.6,p< 0.001, I2¼ 88), sensitivity analyses indicated no differencein conclusions with any single study removed, and cumula-tive analysis showed that results become more positive overtime. When poor quality studies were removed, results re-mained statistically significant (SMD 2.17; 95% CI: 1.20, 3.13;five studies) and heterogeneity remained (Q-value¼ 43.4,p< 0.001, I2¼ 91). Two (2) studies were clear outliers.32,33

These studies included 21 and 61 participants, respectively(10% of our sample) and utilized a summed weekly pain scorein addition to including only subjects with high baseline painscores. When removed from the analysis, heterogeneity wasreduced nominally (Q-value¼ 19.18, p< 0.002, I2¼ 74) and

the SMD dropped to 1.01 (95% CI: 0.51, 1.51). The overallstrength of evidence for efficacy of auriculotherapy for painwas rated as moderate (Table 2).

Perioperative pain

Eight (8) studies assessed perioperative auriculotherapy.Two (2) studies assessed intraoperative use for anestheticrequirement,31,41 and six studies reported on the effects ofpostoperative auriculotherapy on pain relief or pain medi-cation use.15,16,30,37,39,40 Three (3) of these studies were ratedas high quality, three were rated fair, and two were ratedpoor (Table 1).

Three (3) studies in this subgroup were excluded from themeta-analysis due to missing data or an outcome measureother than analgesic use.31,39,40 Analgesic consumption wassignificantly lower in the auriculotherapy group comparedto controls (SMD 0.54; 95% CI: 0.30, 0.77; five studies) (Fig.2B). Statistical heterogeneity did not exist for this subgroupof studies (Q-value¼ 4.48, p¼ 0.35, I2¼ 10.62, t2¼ 0.007).Sensitivity analyses indicated no differences in the conclu-sions with any single study removed. All studies included

FIG. 1. Flow chart of screened,excluded, and analyzed studies. RCT,randomized controlled trial; AT,auriculotherapy.

1100 ASHER ET AL.

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FIG. 2. Standardized mean differences (SMD) and 95% confidence interval (CI) (lower limit, upper limit). A SMD >0indicates less pain (pain score) or less analgesic use (pain medication use) with auriculotherapy compared to control. A largerforest plot point reflects a study with heavier relative weight. The final row in each table represents the test for overall effect.


for this analysis were rated either good or fair quality. Of thethree studies not included, two were rated poor and reportedeither mixed or negative results, and one study was ratedgood that reported favorable results. The strength of evi-dence for efficacy for this subgroup was rated as moderate(Table 2).

Four of the five studies included in the perioperativesubgroup15,16,37,41 examined the effect of auricular acupunc-ture at true acupoints compared to sham points, allowing fora comparison of the effect of point specificity. Meta-analysisfor these studies show a significant reduction in analgesic usefor the true acupuncture group (SMD 0.63; 95% CI: 0.88, 4.97;four studies). Significant heterogeneity was not detectedamong this subgroup of studies (Q-value¼ 1.79, p¼ 0.62,I2< 0.001, t2< 0.001), and sensitivity analysis indicated nodifferences in conclusions with any single study removed.This was the only group of studies that compared the effectsof penetrating true and sham acupuncture.

Acute pain

We identified four eligible studies of auriculotherapy foracute pain. One (1) study, however, did not provide enoughdata to be included in the meta-analysis.17 The pain etiologiesstudied were the following: hip fracture17; biliary colic38;wound debridement in burn patients42; and acute pain from avariety of different pain etiologies among patients in anemergency care center.18 We rated only one study as goodquality. Of the remaining three studies, one was rated fair,and two were rated poor (Table 1).

Because of the different scales used for primary outcomemeasures within this group, only two studies reported suffi-cient data for meta-analysis (Fig. 2C).18,42 The results com-

paring SMD for decrease in pain from baseline to end ofstudy between treatment and control group favor aur-iculotherapy (SMD 1.35; 95% CI: 0.08, 2.64; two studies).There was significant heterogeneity between these two stud-ies (Q-value¼ 6.94, p< 0.001). The two studies not included inthis subgroup analysis both reported positive effects for aur-iculotherapy. The strength of evidence for efficacy of thissubgroup was rated as low (Table 2).

Chronic pain

Five (5) studies using auriculotherapy to treat chronicmusculoskeletal pain met our inclusion criteria. The range ofconditions studied included chronic neck,33 low back,32 can-cer,14 temporomandibular joint,43 and distal extremity pain.44

Of the five studies, two were rated good, one was rated fair,and two were rated poor (Table 1).

The overall change in pain score shows significant im-provement for acupuncture treatment versus control (SMD1.84; 95% CI: 0.60, 3.07; five studies). Significant heterogeneitywas detected among the studies (Q-value¼ 49.54, p< 0.001)(Fig. 2D). However, sensitivity analysis indicated no differ-ences in the conclusions with any single study removed, andcumulative analysis showed that effect estimates becamelarger with later publication dates. When poor quality studieswere removed, results still favored auriculotherapy (SMD2.86; 95% CI 0.70, 5.02; three studies). The strength of evidencefor efficacy of this subgroup was rated as low (Table 2).

Adverse events

Of the 17 studies included in this review, 7 (41%) did notreport on adverse events, 5 (29%) reported no adverse events,

Table 2. Comparative Efficacy of Auriculotherapy for Treatment of Pain

Number of studies(no. of subjects) Design Quality Consistency

Magnitude of effect(95% CI; no. of studies

in meta-analysis)Other modifying

factorsaOverall strength

of evidence

All pain types combinedOutcomes: analgesic use or change in pain score17 (1009) RCT Good (6); Fair

(5); Poor (6)High For change in pain score:

SMD 1.56 (0.85, 2.26;eight)

None Moderate

Perioperative painOutcomes: analgesic use or change in pain score8 (551) RCT Good (3); Fair

(3); Poor (2)High For analgesic use: SMD

0.54 (0.30, 0.77; five)Most studies were

done by sameresearch team.Analgesic use isa proxy for painintensity.

Moderate

Acute painOutcome: change in pain score4 (197) RCT Good (1); Fair

(1); Poor (2)High SMD 1.35 (0.08, 2.64; two) none Low

Chronic painOutcome: change in pain score5 (261) RCT Good (2); Fair

(1); Poor (2)High SMD 1.84 (0.60, 3.07; five) none Low

aImprecise or sparse data, a strong or very strong association, high risk of reporting bias, evidence of a dose response gradient, effect ofplausible residual confounding.

CI, confidence interval; RCT, randomized controlled trial; SMD, standardized mean differences.

1104 ASHER ET AL.

and 5 (29%) reported some acupuncture-related adverseevent. All 10 studies that reported on adverse events (4445needle punctures) used indwelling auricular needles for boththe intervention and control procedures, except for onestudy39 that used auricular needles for the intervention pro-cedure and placebo pill for the control. The most commonlyreported events were ear pain (n¼ 16) and tiredness (n¼ 16).Other events reported include local minor bleeding (n¼ 2),dizziness and nausea (n¼ 1), and headache (n¼ 1). No in-fections or other serious adverse events associated with aur-iculotherapy were reported.

Discussion

We found a large difference between auriculotherapy andcontrol for reduction in pain scores for a wide variety oftypes of pain. The overall SMD was 1.56 (95% CI: 0.85, 2.26),indicating that on average, the mean decrease in pain scorefor the auriculotherapy group was 1.56 standard deviationsgreater than the mean decrease for the control group (i.e., themean of the auriculotherapy group was at the 94th percen-tile of the control group). Removing two outliers reduced theeffect size somewhat (SMD 1.01), but for either estimate, theeffect size is considerably large. For comparison, a recentmeta-analysis of traditional acupuncture for all types of painfound effect sizes (SMD) of 0.17 for body acupuncture versusplacebo acupuncture, and 0.42 for placebo acupunctureversus no acupuncture.45 It is unclear what accounts for thelarge effect sizes found for these studies. Adequate blindingprocedures are often challenging for studies of acupunc-ture, with acupuncturists often unblinded and questionableblinding of participants. However, the studies with the bestblinding procedures tended to have the highest effect esti-mates.16,31–33,37,43 Additionally, when poor quality studieswere removed, which are more likely to contain unmeasuredbias, the effect estimates remained relatively unchanged.

Subgroup analyses for postoperative, acute, and chronicpain also revealed significant reductions in either pain scoresor analgesic consumption. In addition, the estimates did notchange significantly when poor quality studies were re-moved. These results are further supported by the results ofthe random effects overall test for effect, sensitivity analyses,and cumulative analyses (Fig. 2).

Postoperative pain was the largest subgroup we analyzedand contained the only results that were not statistically het-erogeneous. We conducted two analyses of this group: studiesmeasuring analgesic use, and studies comparing penetratingauricular acupuncture at true acupoints verses nonacupunc-ture points. Similar to a recent review of auriculotherapy forpostoperative pain,19 results for analgesic use suggest thatauriculotherapy, specifically indwelling auricular acupunc-ture, is effective at reducing postoperative pain.

Perhaps more interesting are the comparisons for pene-trating auricular acupuncture at true acupoints versus non-acupuncture points, since this comparison controls for theeffects of needle puncture, demonstrating the effect of trueacupuncture points. Our results suggest that for auricularacupuncture, pain relief may be dependent on the use of trueacupuncture points. In contrast, the results of several recentstudies of full body acupuncture suggest that the effects ofacupuncture may be related simply to skin penetration andnot to the use of true acupuncture points.13,46–48 Two (2)

considerations may help explain these discordant findings:(1) the effects of auriculotherapy may indeed be point spe-cific and work through different mechanisms than full bodyacupuncture, or (2) auriculotherapy is not point specific butmay have regional specificity.

The regional innervations of the ear remain an unexploredarea of investigation for auriculotherapy. The auricle receivesnerve fibers from three distinct but overlapping groups:fibers from the superior cervical plexus largely innervate thehelix and lobe; the pinna is innervated by the trigeminalnerve; and the conchae are predominantly innervated bythe vagus nerve with some facial and glossopharyngealnerve innervations.49 It is possible that the effects noted inthe subgroup analysis comparing auricular acupuncture attrue acupoints versus nonacupuncture points are due to theregional grouping of the needles. In all four of these studies,the intervention treatment points were located in the con-chae, while the control points were located along the helix. Ithas been demonstrated that needle stimulation of the con-chae can induce significant parasympathetic stimulation.50 Itis possible that regional specificity, and not point specificity,is responsible for the results of these studies.

The results from studies of acute pain, though in favor ofauriculotherapy, are difficult to generalize because only twostudies were included in that meta-analysis. Likewise, be-cause of the clinical heterogeneity among the studies ofchronic pain, interpretation and generalizability of these re-sults are limited. While it is possible that auriculotherapyanalgesia works via central mechanisms that are independentof the type of pain experienced, there are a paucity of data onthe mechanisms that might be responsible for auriculotherapyanalgesia and there are not yet enough high quality studiesacross the wide spectrum of chronic pain syndromes to beconfident that our results are generalizable to all chronic painconditions. However, the positive results from analyses ofthese two subgroups do add a little information, in favor ofauriculotherapy, to our overall conclusion that auriculo-therapy appears to be beneficial for pain reduction across awide spectrum of pain conditions. Further studies to elucidatethe mechanisms responsible for acupuncture analgesia, andhigh quality studies of clinical pain syndromes will help tofurther clarify the benefits of auriculotherapy.

Overall, we rated the strength of evidence for efficacy ofauriculotherapy compared to control for the treatment ofpain as moderate (Table 2). This was based on the magnitudeof the mean differences we found overall and for each sub-group, the high consistency in direction and magnitude ofeffects noted throughout the studies, the lack of evidence ofpublication bias, the preponderance of good and fair qual-ity studies, and the stability of our estimates with poorquality studies removed. Although we acknowledge thegenerally low strength of evidence of efficacy for acute andchronic pain subcategories, overall we note that the directionof effect appears to favor efficacy of auriculotherapy.

Limitations

Our search identified two studies that may have beenappropriate to include in our review but were unavailable inEnglish.51,52 Additionally, since our search strategy includedonly U.S. and European databases, we may have overlookedstudies contained in the Asian literature.53 However, it has


been noted that studies of acupuncture that are indexed inMEDLINE and published in English score significantlyhigher on standardized quality scales than those that do notmeet these criteria,54 and some countries have been shown topublish exclusively positive results for studies of acupunc-ture.55 For these reasons, we believe our results likely reflectthe results of higher quality studies and reduced publicationbias. For the meta-analyses, significant heterogeneity existedfor all groups analyzed except for the perioperative sub-group. Though heterogeneity among pooled results maylimit the strength of our findings, we note that most trialsshowed positive effects for auriculotherapy, sensitivity ana-lyses revealed that results were not influenced by any singlestudy, and cumulative analyses most often showed thatstudies became more significant over time. Additionally,because random-effects models were used for the conclu-sions of the current study, homogeneity was not assumed forthese analyses.29 However, we recognize that the magnitudeof the effect estimates found may reflect biases that are dif-ficult to overcome in studies of acupuncture.

Conclusions

The evidence from this review suggests that aur-iculotherapy may be effective for the treatment of a variety oftypes of pain, especially postoperative pain, and may be areasonable adjunct for patients having difficulties withpharmacologic pain therapies.

Acknowledgments

We would like to thank Denise Esserman, PhD for herhelp in reviewing some of the trials, and participants of theUniversity of North Carolina NRSA Primary Care Researchfellowship for reviews of the manuscript. Financial supportwas provided by National Institutes of Health/NationalCenter for Complementary and Alternative Medicine grantT32AT003378 (GNA), and NIH/NIGMS grant T32GM081057(SJW).

Disclosure Statement

No competing financial interests exist.

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Address correspondence to:Gary N. Asher, MD, MPH

Department of Family MedicineUniversity of North Carolina at Chapel Hill

590 Manning Drive, CB#7595Chapel Hill, NC 27599

E-mail: [email protected]

(Appendix follows?)


Appendix. Quality Ratings and Assessment Items

Author Quality rating A B C D E F G H I J K L

Alimi14 Good þ þ Yes þ þ/� NR þ þ Mod Yes þ þBarker17 Good þ þ Yes þ NR þ þ þ None No � þSator-Katzenshlager33 Good þ þ No þ þ þ þ þ Low No þ þSator-Katzenshlager31 Good þ þ Yes þ þ þ þ þ Low No þ þUsichenko41 Good þ þ Yes þ þ � þ þ Low No þ NRUsichenko15 Good þ þ Yes þ þ � þ NR Low No þ þGoertz18 Fair þ þ No þ þ � � þ Mod NR þ NRMichalek-Sauberer30 Fair þ NR No þ NR þ þ þ Mod No þ NRSator-Katzenshlager32 Fair þ þ/� No þ NR � � þ Low No þ þUsichenko16 Fair þ þ Yes þ þ þ þ NR Mod No � þUsichenko37 Fair þ þ No þ þ þ þ NR Low No � þGu38 Poor NR NR NR NR NR NR NR NR NR NR NR NRLewis42 Poor þ/� þ NR þ NR NR þ NR High No NR NRLi39 Poor þ NR Yes þ/� NR þ/� þ/� NR None NR NR NRLongobardi44 Poor þ/� þ No þ NR NR þ NR None No þ NRMazzetto43 Poor þ/� þ/� NR þ þ þ þ NR None No þ þWigram40 Poor þ/� NR No � NR NR NR þ None No � NR

A, randomization; B, allocation concealment; C, groups similar at baseline; D, eligibility criteria; E, outcome assessors blinded; F, careproviders blinded; G, participants blinded; H, reporting of adherence; I, attrition; J, high differential attrition (>15%); K, intention-to-treatanalysis; L, postrandomization exclusions.þ, item adequately reported; –, item reported but not performed; þ/–, item performed but method not fully described; NR, not reported.

1108 ASHER ET AL.

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