Immediate Effects of Acupuncture for Managing Myofascial Trigger-Point Pain: A Pilot Study

Abstract

Background:

Myofascial pain syndrome (MPS) is a chronic pain disorder that continues to challenge researchers and clinicians. Current treatments for MPS include trigger-point injections, dry needling, acupuncture, and transcutaneous electrical nerve stimulation. However, it is not known which of these treatment modalities is most effective.

Objective:

The immediate effects of trigger-point acupuncture in myofascial pain and heart rate variability (HRV) were assessed.

Design, Setting, and Patients:

Eight female patients with a mean age of 26.4±9.3 years, who had MPS participated in this study.

Intervention:

The trapezius and rhomboid muscles were examined for myofascial trigger points. The painful myofascial trigger points were identified by palpation, and trigger-point acupuncture was performed.

Main Outcome Measure:

Pain level and HRV were the primary outcomes measured. Baseline and post-treatment pain assessment was performed using a visual analogue scale. HRV was analyzed using electrocardiographic signs that were recorded throughout the treatment protocol.

Results:

Acupuncture at trigger points significantly decreased pain scores from 7.1±1.7 to 3.6±1.6 (p=0.00028), while it had no significant effect on HRV.

Conclusions:

These preliminary results suggest that myofascial trigger-point acupuncture can be an effective method for relieving MPS-related pain.

Introduction

Myofascial pain syndrome (MPS) is a chronic pain disorder characterized by sensorial, motor, and autonomic symptoms involving associated sensitive points in muscles (trigger points). These trigger points, called myofascial trigger points (MTrPs), are highly localized and hyperirritable spots in taut bands of skeletal-muscle fibers and can cause tenderness, referred pain, and a local twitch response.^1,2 MTrPs can be generated by incorrect posture, weight overload, and physical and emotional stress, and can cause muscular tension in a specific muscle or in associated muscle groups.^1,3 Interestingly, MPS is more prevalent in women than in men.

Currently, treatment of MPS includes trigger-point injections, dry needling, acupuncture, and transcutaneous electrical nerve stimulation (TENS). However, it is not known which of these treatment modalities is most effective. Most studies investigating the effectiveness of acupuncture for treating MPS use standard acupuncture points to manage MTrP pain. However, some findings suggest that MTrPs can be used in a manner similar to a treatment site for acupuncture.⁴ Trigger-point acupuncture can provide immediate pain relief in hyperirritable points. In addition, it has been suggested that MTrPs and acupuncture points are similar in many aspects, such as in location and distribution, pain and referred pain patterns, local twitch responses (De Qi), and their relationships to the spinal cord.^5,6 Therefore, musculoskeletal pain relief obtained by acupuncture does not have to be limited to classical acupuncture points on the meridians⁴ and can include MTrPs.

Clinical trials investigating the use of acupuncture for treating myofascial pain have reported conflicting results caused by methodological shortcomings. There is a considerable amount of data that support the efficacy of acupuncture in general, but it remains unclear whether trigger-point acupuncture is effective for treating MPS.^5,6 Therefore, this study was conduction determine the immediate effects of trigger-point acupuncture for managing myofascial pain and heart rate variability (HRV).

Methods

Participants

Eight female patients with a mean age of 26.4±9.3 years, who had MPS participated in this study. Patients that complained of localized neck pain with a palpable taut muscle band were included in the study. Patients with medical conditions were included if they had been receiving the same medication(s) at the same dosage(s) for 1 month or longer. Patients with major trauma, systemic disease, conflicting or ongoing treatments (e.g., cardio-depressive and cardio-stimulating medications), cardiovascular disease, and/or severe hypertension were excluded from the study.

The study was approved by the Ethics Committee in Research of the University of Vale do Paraíba (ECR/UNIVAP, protocol number H122/2010, Brazil) and the procedures followed were in accordance with the Declaration of Helsinki (1975, revised in 1983). Written informed consent was obtained from all participants after patients were informed about the study aims and procedures.

Study Design and Treatment Procedure

The study consisted of a single session. Vital signs and patient history were obtained for each participant. Patients were also evaluated with a postural examination. Briefly, subjects were positioned in a quick massage chair (Beltex^®) to examine the trapezius and rhomboid muscles for MTrPs. Painful MTrPs were detected by bilateral palpation, and pain assessment was performed using a visual analogue scale (VAS).^7,8 The correct application of the technique required experience in palpation and localization of tender points in taut bands of skeletal muscle. Approximately 6–7 MTrPs in the trapezius and/or rhomboid muscles were selected for each individual.

After evaluation and selection of MTrPs, the patients rested for 6 minutes before treatment with trigger-point acupuncture. An acupuncturist with 5 years of training and clinical experience performed the treatment procedure. Disposable stainless steel needles (0.25×30 mm, DongBang^®) were inserted into the skin in the MTrPs to a depth of approximately 3 mm. Needles were manipulated until the subject felt acupuncture sensation (De Qi). Needles were retained in their final positions for an additional 20 minutes, during which the needles were rotated counterclockwise every 5 minutes. After treatment, the needles were removed, and patients were allowed to recover for an additional 6 minutes. The entire treatment protocol from evaluation to final rest period lasted 32 minutes.

Outcome Measures

Primary outcome measures were pain intensity, which was quantified using a 100-mm VAS, and HRV. The VAS measurement was assessed immediately before the first treatment (baseline) and after each treatment (post-treatment). HRV was measured during the entire 32-minute session.

Measurement of pain intensity using the VAS

Pain intensity was measured qualitatively using a 100-mm horizontal line with descriptive phrases along its length ranging from “no pain” at one end to “worst possible pain” at the other. There were no other marks on the VAS visible to the subject. Before treatment, subjects were asked to draw a vertical line at the appropriate position on the VAS that best described baseline pain intensity level. After treatment, patients were asked to mark post-treatment pain intensity level.

Research has established that the VAS is a valid and sensitive method to measure pain intensity in patients with acute or chronic pain.^9,10 The VAS also provides reliable repetition of measurements.

Measurement of HRV

The eletrocardiographic signals (R–R intervals) were obtained using a frequency meter (S810i, Polar Electro, Finland) throughout the treatment protocol for 32 minutes. The data were transmitted to a computer equipped with the Polar Precision Performance Software v4 (Polar Electro,^® Finland), and the signal was filtered and exported to formatted text files (.txt files). Finally, the data were analyzed by HRV Analysis Software v2.0 (University of Western Finland, Finland) for time domain and frequency. Considering that there are many factors that can influence HRV, such as circadian rhythm, body position, prior activity level, and types of medication, precautions were taken to maintain conditions constant and similarity for each patient, such as time of day and sitting body position after an adaptation period of 10 minutes.

Analysis of HRV

For frequency-domain HRV analysis, Fast Fourier Transform, was used to calculate the very low–frequency (VLF, 0-0.04 Hz), low-frequency (LF, 0.04-0.15 Hz), and high-frequency (HF, 0.15-0.4 Hz) components, as well as LF and HF components in normalized units (LFun and HFun, respectively). LF was considered to reflect sympathetic and parasympathetic activity, and HF was considered to reflect parasympathetic activity. The autonomic balance was obtained by the ratio between the sympathetic and parasympathetic areas (LF/HF), in which ratios >1 were representative of sympatheticotonia and those <1 indicated vagotonia, while a ratio of 1 indicated sympathovagal balance. VLF is not a well-defined physiological phenomenon and may be related to the renin–angiotensin–aldosterone system, thermoregulation, and peripheral vasomotor tone.¹¹

For the HRV time-domain analysis, the following variables were calculated: the average normal R–R intervals (RRmed); the standard deviation (SD) beat-to-beat (N–N) intervals (SDNN, measured in ms); the number of pairs of successive N–Ns that differed by more than 50 ms (N–N50); the proportion of N–N50 divided by total number of N–Ns (pNN50); and the square root of the mean squared difference of successive N–Ns (RMSSD).

Statistical Analysis

The data were statistically analyzed using a paired Student's t-test and reported as mean±SD. The level for statistical significance was set at p<0.05. Comparisons were made before (baseline) and after treatment (post-treatment).

Results

To determine the effect of trigger-point acupuncture on pain level and HRV, 8 female patients were treated with the 32-minute treatment protocol described above. Baseline and post-treatment pain-level assessments were collected using a VAS. The results were expressed as the mean and respective SDs. Table 1 shows the results of the anthropometric data.

Table 1.

Participants' Characteristics

Participants' characteristics	Average±SD
Age (years)	26.4±9.31
Height (cm)	1.60±0.04
Weight (Kg)	61.6±15.4
BMI (Kg/m2)	19±4.52
Menstrual period	Luteal phase

SD, standard deviation, BMI, body mass index.

These results also indicate that trigger-point acupuncture decreased pain levels significantly from 7.1±1.7 to 3.6±1.6 on the VAS (p=0.00028; Fig. 1). For the analyzed subjects, the average percent of improvement post-treatment was 49.41±0.19%. Four subjects (50% of the population) had values greater than this percentage, which indicated a clinically significant improvement as reflected in the VAS (Table 2).

FIG. 1.

Pain score pre–post trigger-point acupuncture treatment (mean±standard deviation). *Significant p-value.

Table 2.

Pain scores Pre- and Post-Treatment for Individual Data and Percent Variation in Post-Acupuncture Trigger-Point Treatment (n=8)

	Pain scores
Pt #	Pre	Post	% Variation
1	8.3	5.3	63.80
2	8.7	2.4	27.50
3	5.8	4.1	70.60
4	7.5	3.1	41.30
5	9.0	4.8	53.30
6	7.3	5.4	73.90
7	3.9	1.0	25.60
8	6.1	2.4	39.30
Average	7.1	3.6	49.41
SD	1.7	1.6	0.19

Pt, patient; SD, standard deviation.

As noted above, HRV was measured throughout the 32-minute procedure (Table 3). Table 3 shows that trigger-point acupuncture had no significant effects on HRV.

Table 3.

Mean Heart Rate and Heart Rate Variability (HRV) for 3 Protocol Periods

Variable	Rest	Trigger-point acupuncture	Post-acupuncture	p
HF	712.8±607.65	1176.6±876.43	848.4±550.71	0.56
LF	833.4±494.88	1415.8±743.79	1327.4±651.05	0.33
VLF	1680.8±1585.05	2699.2±807.225	2579.6±1165.27	0.38
LF/HF	183±0.38	2.06±0.85	2.77±0.65	0.10
LFun	58.7±13.09	59.64±11.22	63.96±12.97	0.78
HFun	41.3±13.09	40.36±11.22	36.04±12.97	0.78
RMSSD, ms	41.24±12.63	52.28±16.71	44.02±11.15	0.44
PNN50	16.98±11.30	21.6±15.69	20.28±14.20	0.85
Heart rate mean, beats/min	77.84±5.72	74.93±6.18	76.10±6.69	0.76
RRmed	779.32±54.52	812.42±66.48	799.7±69.24	0.71
SDNN, MS	61.16±10.85	75.38±15.00	71.74±7.92	0.17

All values are mean±standard deviation (SD).

HF, high frequency; LF, low frequency; VLF, very low frequency; LF/HF, low frequency/high frequency ratio; LFun, normalized low frequency; HFun, normalized high frequency; RMSSD, square root of the sum of successive differences between adjacent normal R–R intervals squared; PNN50, percentage of normal R–R intervals differing > 50 ms of the adjacent R–R; RRmed, average of normal R–R intervals; SDNN, SD of the range N–N, measured in ms.

Discussion

MPS is a common health problem, and patients with MPS often complain of regional pain that most frequently occurs in the head, neck, and upper back regions of the body. The typical muscles involved are the trapezius, supraspinatus, and rhomboids, but other muscles can be also involved.¹² Many therapy modalities, such as trigger-point injections of local anesthetics into MTrPs, deep or superficial dry needling, TENS, and acupuncture, have been used to treat MPS and manage pain resulting from this chronic condition.¹³ Although trigger-point injection is the most widely used method of treatment, other methods, such as acupuncture, appear to be effective for MPS management.¹³

Acupuncture is a well-known method for relieving chronic pain, with an efficacy that is similar to trigger-point injection in MPS, indicating that acupuncture may be an efficient treatment for MPS.⁵ Indeed, Ga et al.⁵ obtained statistically similar results regarding pain scores and range of neck movement in patients with MPS of the upper trapezius, using both 0.5% lidocaine injection and acupuncture needling at MTrPs. However, the most effective form of acupuncture for treating MPS is still unclear. It has been suggested that needle penetration in standard acupuncture points evoke small, local twitches that contribute to pain relief, but the duration of these twitches may not be long enough for effective treatment.¹² Interestingly, research has identified acupuncture at trigger points as an efficient method of pain relief and as an anti-inflammatory aid.^5,6 Therefore, this study was conducted to evaluate the efficiency of trigger-point acupuncture for pain relief and the effects on HRV in patients with MPS.

This study showed that acupuncture at trigger-point sites decreased pain scores on the VAS. This therapeutic effect of trigger point acupuncture may be related to production of a local twitch response or De Qi during needle penetration or manipulation.^14,15 For example, the acupuncture needles were inserted into the trigger points by applying standard rotating, lifting, and thrusting techniques. A recent study has shown that these needle manipulation techniques cause winding of subcutaneous collagen fibers, which may allow needle movements to deliver a mechanical signal to the tissue. Such a mechanical cue may be the key to the therapeutic mechanism of acupuncture.

MTrPs are thought to be sites where nociceptors, such as polymodal-type receptors, reside. When MTrPs are stimulated mechanically by acupuncture and a local twitch response is induced, spinal-inhibitory effects may be initiated that relieve pain.¹⁶ In fact, large quantities of peptides and neurotransmitters that can excite nociceptors directly or indirectly, such as substance P, histamine, and 5-hydroxytryptamine (5-HT), are released after mechanical stimulation of mast cells.^17,18

In the model proposed by Melzack and Wall¹⁹ (1965, cited Pereira²⁰), acupuncture works by stimulating A-β sensory fibers, whereby they directly inhibit the transmission of pain by small A-δ and C fibers.¹⁶ Another possible mechanism that leads to a decrease in pain scores is the release of opioid peptides.^21,22 As a result, consequences of mechanical stimulation, mechanotransduction, and cellular responses, together, lead to the clinical effects of acupuncture, such as pain relief.

Given that chronic pain can be harmful to the cardiovascular system, pain relief may promote restoration of cardiovascular health by increasing HRV.²³ The current study's results did not show any significant alterations in HRV, although the SDNN index increased with trigger-point acupuncture. It is possible that a larger sample size is necessary to observe any significant effects of trigger-point acupuncture on HRV. The HRV may also need to be monitored for a longer period of time to detect significant changes resulting from treatment, because immediate restoration cannot occur in a system that has sustained chronic harm.

Preliminary research suggests that acupuncture needling can influence HRV. There is evidence that traditional acupuncture causes changes in HRV as a result of the needles stimulating sensory nerves, which, in turn, alter release of neurotransmitters—such as serotonin, acetylcholine, and nocicepitina—in the central nervous system.^24,25 Moreover, the reduction of heart rate may be associated with the release of inhibitory neurotransmitters—such as endorphins, enkephalins, and possibly endomorphins—in the hypothalamus, brainstem, and spinal neurons that promote the reduction of sympathetic premotor neuron activity.²⁵ In addition, release of endogenous opioids that act as neuromodulators reduces the role of excitatory neurotransmitters in the brain and spinal cord and decreases the heart rate by facilitating cardiac vagal activity and suppressing sympathetic nerve activity.^25–27 Given that no effect of trigger point acupuncture was noted on HRV, despite the fact that there is substantial evidence that acupuncture can affect HRV, the current authors plan to expand these findings in future studies by recording the R–R interval and performing pain-score analysis 24 and 48 hours after treatment. In addition, the current authors will include a standard acupuncture-needling group, and sham-acupuncture and placebo groups for comparative analysis in the future. A placebo is required for future trials to test the effectiveness of trigger-point acupuncture treatment. Moreover, assessment is needed to determine if the effects are similar on pain and HRV as well as to determine the most effective treatment method.

Conclusions

These preliminary results suggest that myofascial trigger-point acupuncture may be effective for relieving pain in patients with MPS and should be evaluated further as a potential standard of care for MPS. Importantly, these effects may contribute to better health and an improvement in quality of life for these patients. However, additional assessment is needed to compare myofascial trigger-point acupuncture with standard acupuncture-needling as well as sham-acupuncture and placebo procedures to determine which of these is the superior method.

Footnotes

Acknowledgments

The authors are thankful to Patricia Goulart, MD, for her help and valuable comments.

Disclosure Statement

No competing financial interests exist.

References

Travell

, Simons

. Myofascial pain and dysfunction. The Trigger Point Manual. Baltimore: Williams & Wilkins, 1999; 1064.

Wolens

. The myofascial pain syndrome: A critical appraisal. Am Phys Med Rehabil., 1998; 12,2:299–316.

Maurício

CRM

, Carvalho

. Physiotherapy Intervention in Myofascial Pain Syndrome [in Portuguese] Foz do Iguaçu, Brazil: Faculty Union of the Americas, 2007.

Chu

. The local mechanism of acupuncture. Zhongghua Yi Xue Za Zhi., 2002; 65,7:299–302.

, Choi

, Park

, Yoon

. Acupuncture needling versus lidocaine injection of trigger points in myofascial pain syndrome in elderly patients—a randomised trial. Acupunct Med., 2007; 25,4:130–136.

Itoh

, Katsumi

, Kitakoji

. Trigger point acupuncture treatment of chronic low back pain in elderly patients—a blinded RCT. Acupunct Med., 2004; 22,4:170–177.

Takiguchi

, Fukuhara

, Sauer

et al. Effect of acupuncture on pain, sleep and quality of life improvement in fibromyalgia patients: Preliminary study. Fisioter Pesqui., 2008; 15,3:280–284.

Ciena

, Gatto

, Pacini

et al. Influence of pain intensity on the unidimensional scales reponses of pain measurement in elderly and young adults population. Semina: Ciênc Biol Saúde., 2008; 29,2:201–212.

Ogon

, Krismer

, Sollner

, Kantner-Rumplmair

, Lampe

. Chronic low back pain measurement with visual analogue scales in different settings. Pain, 1996; 64,3:425–428.

10.

Breivik

, Bjornsson

, Skovlund

. A comparison of pain rating scales by sampling from clinical trial data. Clin J Pain, 2000; 16,1:22–28.

11.

Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Heart rate variability: Standards of measurement, physiological interpretation, and clinical use. Eur Heart J., 1996; 17,3:354–381.

12.

Kung

, Chen

, Chaung

, Chou

, Tsai

, Hwang

. Evaluation of acupuncture effect to [sic] chronic myofascial pain syndrome in the cervical and upper back regions by [sic] the concept of meridians. Acupunct Electother Res., 2001; 26,3:195–202.

13.

Han

, Harrison

. Myofascial pain syndrome and trigger-point management. Reg Anesth., 1997; 22,1:89–101.

14.

Langevin

, Yandow

. Relationship of acupuncture points and meridians to connective tissue points. Anat Rec., 2002; 269,6:257–265.

15.

Langevin

, Churchill

, Fox

, Badger

, Garra

, Krag

. Biomechanical response to acupuncture needling in humans. J Appl Physiol., 2001; 91,6:2471–2478.

16.

Sheng-Xing

. Neurobiology of acupuncture: Toward CAM. eCAM, 2004; 1,1:41–47.

17.

Zhao

. Neural mechanism underlying acupuncture analgesia. Prog Neurobiol., 2008; 85,4:355–375.

18.

Meyer

, Ringkamp

, Campbell

, Raja

. Peripheral mechanisms of cutaneous nociception. McMahon

, Koltzenburg . Wall and Melzack's Textbook of Pain. Philadelphia: Elsevier, 2006; 3–34.

19.

Melzack

, Wall

. Pain mechanisms: A new theory. Science, 1965; 150,3699:971–979.

20.

Pereira

, Sousa

FAEF

. Measurement and evaluation of postoperative pain: A brief review [in Portuguese] Rev Latino-Am Enfermagem., 1998; 6,3:77–84.

21.

Wilson

. Biophysical modeling of the physiology of acupuncture. J Altern Complement Med., 1997; 3,1:25–39.

22.

Asamoto

, Takeshige

. Activation of the satiety center by auricular acupuncture point stimulation. Brain Res Bull., 1992; 29,2:157–164.

23.

Storella

, Shi

, O'Connor

, Pharo

, Abrams

, Levitt

. Relief of chronic pain may be accompanied by an increase in a measure of heart rate variability. Anesth Analg., 1999; 89,2:448–450.

24.

Haker

, Egekvist

, Bjerring

. Effect of sensory stimulation (acupuncture) on sympathetic and parasympathetic activities in healthy subjects. J Auton Nervous Syst., 2000; 79,1:52–59.

25.

Vogel

JHK

, Bolling

, Costello

et al.

Integrating Complementary Medicine Into Cardiovascular Medicine: A Report of the American College of Cardiology Foundation Task Force on Clinical Expert Consensus Documents (Writing Committee to Develop an Expert Consensus Document on Complementary and Integrative Medicine)

J Am Coll Cardiol., 2005; 46,1:184–221.

26.

Chao

, Shen

, Tjen-A-Looi

, Pitsillides

, Peng

, Longhurst

. Naloxone reverses inhibitory effect of electroacupuncture on sympathetic cardiovascular reflex responses. Am J Physiol., 1999; 276,6[pt2]:H2127–H2134.

27.

Nishijo

, Mori

, Yosikawa

, Yazawa

. Decreased heart rate by acupuncture stimulation in humans via facilitation of cardiac vagal activity and suppression of cardiac sympathetic nerve. Neurosci Lett., 1997; 227,3:165–168.