Remote Influences of Acupuncture on the Pain Intensity and the Amplitude Changes of Endplate Noise in the Myofascial Trigger Point of the Upper Trapezius Muscle

Article Outline

• Abstract
• Methods
  • General Design
  • Patients
  • Identification of Myofascial Trigger Points
  • Identification of Acupuncture Points
  • Treatment Procedures
  • Assessment of Subjective Pain Intensity (Numerical Pain Rating Scale)
  • Assessment of Changes in Endplate Noise
    • Equipment
    • Procedure of searching EPN loci
    • Measurement of EPN amplitude
  • Statistical Analysis
• Results
  • Demographic Information
  • Pain Intensity (Numerical Pain Rating Scales)
  • Mean Amplitude of EPN
  • Correlation Between Changes in Pain Intensity and Changes in Mean Amplitude of EPN
• Discussion
  • Summary of Important Findings in This Study
  • EPN Amplitude and Irritability of MTrP
  • Changes in EPN Amplitudes After Distal Needling
  • Mechanism of Acupuncture for Pain Control
  • Study Limitations
• Conclusion
• References
• Copyright

Abstract 

Chou L-W, Hsieh Y-L, Kao M-J, Hong C-Z. Remote influences of acupuncture on the pain intensity and the amplitude changes of endplate noise in the myofascial trigger point of the upper trapezius muscle.

Objective

To investigate the remote effect of acupuncture on the pain intensity and the endplate noise (EPN) recorded from a myofascial trigger point (MTrP) of the upper trapezius muscle.

Design

Randomized controlled trial.

Setting

University hospital.

Participants

Patients (N=20) with active MTrPs in upper trapezius muscles and no experience in acupuncture therapy.

Interventions

Patients were divided into 2 groups. Those in the control group received sham acupuncture, and those in the acupuncture group received modified acupuncture therapy with needle insertion into multiple loci to elicit local twitch responses. The acupuncture points of Wai-guan and Qu-chi were treated.

Main Outcome Measures

Subjective pain intensity (numerical pain rating scale) and mean EPN amplitude in the MTrP of the upper trapezius muscle.

Results

The pain intensity in the MTrP was significantly reduced after remote acupuncture (from 7.4±0.8 to 3.3±1.1; P<.001), but not after sham acupuncture (from 7.4±0.8 to 7.1±0.9; P>.05). The mean EPN amplitude was significantly lower than the pretreatment level after acupuncture treatment (from 21.3±9.5μV to 9.5±3.5μV; P<.01), but not after sham acupuncture treatment (from 19.6±7.6μV to 19.3±7.8μV; P>.05). The change in the pain intensity was significantly correlated with the change of EPN amplitude (r = 0.685).

Conclusions

Both subjective changes in the pain intensity and objective changes of the EPN amplitude in the MTrP region of the upper trapezius muscle were found during and after acupuncture treatment at the remote ipsilateral acupuncture points. This study may further clarify the physiological basis of the remote effectiveness of acupuncture therapy for pain control.

Key Words: Acupuncture, Electromyography, Trigger points, myofascial, Pain, Rehabilitation

List of Abbreviations: EMG, electromyography, EPN, endplate noise, LTR, local twitch response, MTrP, myofascial trigger point

ACUPUNCTURE THERAPY HAS been widely used for treating patients with musculoskeletal pain.¹, ², ³, ⁴, ⁵ In many cases, the sites of acupuncture needling are selected in regions remote to the painful site.⁶, ⁷, ⁸, ⁹ The physiological basis for this remote effect is still uncertain. It has been found that the distribution of acupuncture points of the same meridian is similar to the pattern of referred pain from certain MTrPs.¹⁰ For example, the connection of the large intestine meridian is located within the territory of the referred pain elicited by stimulation of the MTrP in the middle scalene. Both are distributed in the anterior and lateral aspects of the upper limb. The similarity between the acupuncture and needling of an MTrP has also been well documented.¹⁰, ¹¹, ¹² It has been hypothesized that the connections of MTrP circuits in the spinal cord is the basic mechanism of the referred pain pattern.¹³, ¹⁴

Clinically, an MTrP is a most tender (hyperirritable) spot in a taut band of skeletal muscle fibers characterized with a specific pattern of referred pain and an LTR.¹⁵, ¹⁶ An LTR is a rapid contraction of muscle fibers in the taut band in response to high-pressure mechanical stimulation. Based on the studies of both human subjects and animals, it has been demonstrated that there are multiple sensitive loci in an MTrP region.¹⁷, ¹⁸ These sensitive loci are probably nociceptors located in the endplate zone.¹⁹ The prevalence of EPN recorded by EMG equipment is significantly higher in an MTrP region than a non-MTrP region,²⁰, ²¹ and is highly correlated with the irritability (sensitivity) of an MTrP.²²

In this study, we investigated the changes in pain intensity and EPN prevalence in the MTrP region of the upper trapezius muscle in patients with chronic pain in the shoulder region during and after acupuncture treatment on the ipsilateral remote acupuncture points in order to confirm the remote effect of acupuncture.

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Methods 

General Design 

The patients were treated with either acupuncture or sham acupuncture therapy on 2 acupuncture points. For every subject, the subjective pain intensity and the objective changes of EPN in the MTrP region of the upper trapezius muscle were assessed before, during, and after the whole course of treatment.

Patients 

Patients for this study were selected from a pain control clinic by a physiatrist who was not involved in the outcome measures. The inclusion criteria included (1) having intolerable chronic pain in 1 side of the shoulder with active MTrPs in the ipsilateral upper trapezius muscle, (2) having no treatment with acupuncture previously, and (3) having poor response to previous conservative and noninvasive treatment, such as oral medicine or physical therapy.

The exclusion criteria for the selection of patients included (1) having conditions with contraindication for needling, such as local infection, malignancy, serious medical problems, taking anticoagulant medicine, pregnancy with threatened abortion, and so forth; (2) taking medicine that might change the pain intensity or pain threshold, such as analgesics, sedatives, substance abuse (including alcohol, narcotics), and so forth; (3) having previous surgery or trauma to the neck, upper back, or upper limb; (4) having history of significant neurologic deficit involving neck or upper limb, either central or peripheral origin; and (5) having evidence of cognitive deficit.

Either the inclusion or the exclusion criteria were assessed by the same physiatrist based on detailed medical history and careful physical examination. The selected patients were randomly divided into acupuncture and sham-acupuncture groups using a computerized randomization program. Every subject signed the consent form, which was approved by our university's institutional review board.

Identification of Myofascial Trigger Points 

The identification of an active MTrP in the upper trapezius muscle was performed with palpation examination. Diagnosis of an MTrP was based on (1) a most sensitive (tender) spot in a palpable taut band and (2) recognized pain (as patient's usual clinical complaints) when this sensitive spot was compressed.¹⁵, ¹⁶, ²³ Other supportive criteria for diagnosis included (1) a typical referred pain pattern as described by Travell and Simons,¹⁵ and (2) a local twitch response elicited by snapping palpation of the MTrP.²³ The identified active MTrP of the upper trapezius muscle was marked (on the skin with an area approximately 1 cm in diameter) for EPN study.

Identification of Acupuncture Points 

A well trained licensed acupuncture instructor performed all the acupuncture procedures, including identification and needling of acupuncture points. Before treatment, 2 acupuncture points, Wai-guan (triple energizer [TE]-5) in the extensor indicis muscle, on the dorsal forearm, between the radius and ulna, 3 cm superior to the dorsal transverse wrist crease, and Qu-chi (large intestine [LI]-11) in the extensor carpi radialis longus muscle, on the lateral side of the cubital crease with elbow in full flexion, were determined and marked. This acupuncturist was not involved in the outcome assessments. These 2 acupuncture points were also MTrPs (Ah-Shi points) as confirmed by palpation examination. In our study, these 2 acupuncture points were selected based on an extensive review of acupuncture literature and the clinical experience in acupuncture therapy by experienced acupuncturists who had practiced in acupuncture for more than 15 years. Both acupuncture points have been frequently selected for the treatment of neck and shoulder pain.⁷, ⁸, ⁹ There was evidence of good results by needling these 2 acupuncture points in our previous experience.²⁴

Treatment Procedures 

The patient was in a comfortable prone position with the head turned to the contralateral side and the ipsilateral upper limb placed near the side of the examination table. This position could allow the simultaneous acupuncture needling to the forearm muscle and recording of EPN from the MTrP of the upper trapezius muscle. In this position, the patient was unable to observe either the procedure of treatment on the forearm or the EMG recording of EPN in the MTrP of the upper trapezius muscle. The skin over the marked acupuncture point was cleaned with alcohol before needle insertion. The disposable acupuncture needle with a size of #30 and a length of 25 cm (1 in) or 37 cm (1.5 in) was used for every patient. In the sham-acupuncture group, the acupuncture needle was inserted into a rubber connector, which was firmly taped on the marked point for acupuncture (fig 1).²⁵ The needle contacted the skin and the patient could feel the sharp needle tip, but the needle did not penetrate into the skin. Then the needle stayed there (without moving the needle) through the whole course of treatment. In the acupuncture group, a newly modified technique was used for acupuncture therapy. The acupuncture needle was inserted into the regular depth in the subcutaneous layer. Similar to the technique of MTrP injection,¹⁶, ¹⁷, ²⁶ the needle was moved in and out in different directions at a speed of about 2cm/s. This in-and-out manipulation was performed with simultaneous rotation of the needle to facilitate the in-and-out movement (screwing in-and-out technique). With this rapid (high-pressure) needle movement, it was much easier to induce the De Qi effect (soreness or pain and/or local twitch responses). When an LTR was elicited, the muscle twitching could cause needling moving or needle grabbing and could always be perceived by the one who was doing needling. To elicit LTRs during needling is essential for complete and immediate pain relief after needling.²⁵ This in-and-out movement continued for 15 seconds, and then the needle was stationary for at least 3 minutes.

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• Fig 1. 

  Sham acupuncture performed in this study with an insertion of acupuncture needle into a rubber connector that was firmly taped on the skin.

The sequence of treatment is expressed in figure 2. For each subject, the Wai-guan point was treated first. About 5 minutes after completing needle manipulation (screwing in-and-out) at Wai-guan, the Qu-chi point was treated with the same procedure, but the acupuncture needle stayed in Wai-guan continuously without any needle movement. Five minutes after completion of needle manipulation at Qu-chi, both needles in these 2 points were manipulated (screwed in and out) simultaneously for 15 seconds, and then stayed quietly for another 3 minutes. The acupuncturist used 2 hands simultaneously to manipulate the needles.

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• Fig 2. 

  Sequences of acupuncture therapy and assessment in the whole course of the experiment.

Assessment of Subjective Pain Intensity (Numerical Pain Rating Scale) 

Pain intensity was assessed with a verbally reported numerical scale in which 0 represented no pain and 10 represented the worst imaginable pain. A scale below 5 was usually considered tolerable pain based on the experience in previous studies. During the remote acupuncture therapy, the patient is usually unable to report the exact pain intensity in the proximal upper trapezius region because of severe pain and discomfort in the distal needling sites. Therefore, the pain intensity in the upper trapezius region was not assessed during the manipulation of the distal acupuncture needle, but was assessed only before and after completion of the whole course of acupuncture therapy (see fig 2).

Assessment of Changes in Endplate Noise 

Intramuscular electrical activity was recorded using 37-mm, disposable, monopolar Teflon-coated EMG needle electrodes. The length of exposed needle tip ranged between 0.4 and 0.5mm. The EMG recordings were measured with a 2-channel portable digital miniature EMG equipment.^a The low-cut frequency filter was set at 100Hz and the high-cut at 1000Hz. The gain was set at 20μV a division for recordings from both the first and second channels. The sweep speed was 10ms a division. The first channel recorded the EMG activity from the active electrode (search needle at the experimental site to search for EPN loci) at the MTrP site. The second channel recorded the EMG activity from the active electrode at a control site (electrically silent site) in muscle tissue adjacent to the MTrP site, where no EMG activity can be recorded and no pain can be elicited at the insertion site of the recording needle connecting the second channel (so that it was not a latent MTrP). Another needle electrode served as the common reference electrode by connecting it to these 2 channels through Y connectors (fig 3). The common reference needle electrode was placed in the subcutaneous tissue approximately 2 to 3cm from the active recording site. In such arrangement, action potentials recorded from the first channel could be confirmed as those recorded exactly from the EPN locus if the recordings from the second channel were flat (electrically silent with no baseline fluctuations higher than 5μV). A ground electrode was placed on the skin of the ipsilateral shoulder. Room temperature was maintained at 21°C±1°C.

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• Fig 3. 

  Searching for EPN and the recorded EPN tracing recorded from the first channel (top right) compared with a control tracing recorded from the second channel (bottom right).

The active recording needle in the first channel was inserted into the MTrP region of the upper trapezius muscle to search for EPN. The recording needle electrode was initially placed in the subcutaneous layer under the marked region at a depth approximately 1 to 2mm in the muscle. Then the needle was advanced gently and slowly through the least possible distance (usually 1–2mm) by simultaneously rotating the needle to facilitate smooth entry through the muscle tissue. The slow advance and rotation technique has been used in previous studies²⁰, ²¹, ²², ²⁷ and contrasts with the rapid thrusting motion generally used by clinical electromyographers. The gentle technique can also reduce the likelihood of eliciting an LTR, which reduces the chance of observing EPN. As soon as an EPN with amplitude higher than 30μV could be recorded, the examiner stopped moving the needle to ensure that this EPN could run continuously on the recording screen with constant amplitudes. Then the needle was fixed firmly with tape to avoid any further movement. Another investigator (acupuncturist) began to perform the acupuncture therapy (see fig 2) as soon as the EPN amplitude was stable. Continuous EPN tracing was recorded through the whole course of acupuncture therapy, providing the opportunity for continuous visual observation of EPN changes on the EMG screen.

Samples of EPN recordings were taken before, at the initiation of, and 3 minutes after the completion of the manipulation of the acupuncture needle (screwing in-and-out) (see fig 2). The mean amplitude of EPN in a period of 10ms was analyzed and calculated by the embedded software in the Neuro-EMG-Micro equipment.

Statistical Analysis 

The mean and standard deviation of the values measured for pain intensity and amplitude of EPN were calculated. The Student t test was used to assess the differences between the data before and after acupuncture treatment (paired t test), and the differences in the data between the acupuncture and the sham-acupuncture groups. The data of pain intensity and EPN prevalence before and after treatment were further normalized as follow: percentage of changes = [(data after treatment – data before treatment)/data before treatment] × 100%. After data normalization, the differences in the changes of pain intensity and EPN prevalence between 2 groups were further compared with the Student t test. The correlation between the changes in pain intensity and those in EPN amplitude was tested with the Kendall coefficient of rank correlation. The confidence interval was set at 95% (P<.05). All data were analyzed using SPSS version 10.0 for Windows.^b

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Results 

Demographic Information 

A total of 20 patients with unilateral MTrPs in the upper trapezius muscle were enrolled for this study. There were 10 subjects in each group. Every patient had pain intensity greater than 5 of 10 for a period longer than 3 months. Table 1 shows the demographic information. There were no significant differences in all data between the 2 groups (see table 1).

Table 1. Demographic Data of Patients

Group	Acupuncture	Sham-Acupuncture	P Value⁎
Total number of subjects	10	10
Age (y)† (range)	37.7±11.3 (23–53)	33.3±7.7 (22–47)	>.05
Sex
Male	4	4	>.05
Female	6	6	>.05
Side
Right	6	6	>.05
Left	4	4	>.05
Pain duration (mo)†	5.9±3.3	5.8±2.8	<.05
Initial pain intensity (0–10)†	7.4±0.8	7.4±0.8	<.05

Pain Intensity (Numerical Pain Rating Scales) 

As shown in table 2, the pain intensity of the upper trapezius muscle was reduced significantly (from 7.4±0.8 to 3.3±1.1; P<.001) after completion of the whole treatment course in the acupuncture group. However, in the sham acupuncture group, there was no significant change in pain intensity (from 7.4±0.8 to 7.1±0.9; P>.05). The difference between 2 groups is further demonstrated in figure 4. After data normalization, the percentage of decrease in pain intensity in the acupuncture group was significantly more than that in the control group.

Table 2. Changes in Pain Intensity After Acupuncture Therapy

NOTE. Values are mean ± SD unless otherwise indicated.

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• Fig 4. 

  Remarkable decrease in the pain intensity after acupuncture therapy compared with that after sham-acupuncture therapy.

At the initiation of the manipulation of the acupuncture needle on the distal acupuncture point, almost all patients recalled an increased pain in the upper trapezius region, but they could not report the pain intensity exactly because the distal pain is much stronger than the proximal. They also remembered that the pain intensity in the MTrP region was reduced gradually after needle manipulation stopped in the distal acupuncture point.

Mean Amplitude of EPN 

For every patient in the acupuncture group, the EPN amplitude increased at the initiation of the manipulation on the acupuncture needle (screwing in and out), and decreased shortly (within a few seconds) after the completion of needle movement. The initial change after needle manipulation was very remarkable in some patients who also recalled an increase of pain intensity in the MTrP region of the upper trapezius muscle.

The changes in the mean EPN amplitude are demonstrated in figure 5. At the initiation of the needle manipulation at the Wai-guan point (initially needled point) in the acupuncture group, there was a tendency (not statistically significant) toward increase in mean EPN amplitude. However, the posttreatment value of mean EPN amplitude decreased remarkably. As soon as the needle manipulation was performed at the Qu-chi point, the mean EPN amplitude increased again and rose to the original level (before treatment). Then the mean EPN amplitude reduced after cessation of needle manipulation at the Qu-chi point. Finally, when simultaneous 2-needle manipulation at these 2 acupuncture points was performed, similar, but much remarkable, changes in the mean EPN amplitude were also observed. In the sham-acupuncture group, no such changes could be observed. The values of the mean EPN amplitude remained at the same level through the whole course of sham acupuncture treatment.

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• Fig 5. 

  Serial changes of EPN amplitudes in the whole course of acupuncture and sham-acupuncture therapies.

Statistical analyses of changes in the mean EPN amplitude are listed in table 3. Compared with the values before acupuncture treatment, there was no significant difference in the mean EPN amplitude between the 2 groups. However, there were significant decreases (P<.01) in the mean EPN amplitude after completion of needle manipulation at each acupuncture point, and at both acupuncture points. After completion of the whole course of acupuncture therapy, the mean EPN amplitude reduced from 21.3±9.5μV to 9.5±3.5μV (P<.01). In the sham-acupuncture group, the changes in the EPN amplitude were all insignificant (P>.05). The mean EPN amplitude was 19.6±7.6μV before sham treatment and was 19.3±7.8μV after treatment (P>.05). There was a tendency that simultaneous 2-needle manipulation had more influence on the changes of the mean EPN amplitude (see fig 5), but this was not statistically significant, probably because of the small sample size.

Table 3. Changes in Mean Amplitude of Endplate Noise After Treatment

Needling in Acupuncture Point	Treatment	Group		P Acupuncture vs Sham⁎
		Acupuncture	Sham-Acupuncture
None	Before treatment	21.3±9.5μV	19.6±7.6μV	.67
Wai-guan	At the initiation of needle manipulation	22.9±13.9μV	19.8±7.5μV	.54
	P value, before vs after	.637	.094
	% Change after treatment	11.24±38.78	1.52±2.01	.44
Wai-guan	3 min after cessation of needle manipulation	13.0±5.6μV	19.6±7.7μV	.04†
	P value, before vs after	.009†	.935
	% Change after treatment	–32.73±25.66	–0.04±2.82	.0008†
Qu-chi	At the initiation of needle manipulation	23.2±18.0μV	19.7±7.8μV	.58
	P value, before vs after	.684	.510
	% Change after treatment	10.83±50.53	0.46±2.82	.53
Qu-chi	3 min after cessation of needle manipulation	11.3±3.5μV	19.6±7.8μV	.01†
	P value, before vs after	.004†	.858
	% Change after treatment	–40.54±20.82	–0.09±3.13	0.9×10−5†
Wai-guan + Qu-chi	At the initiation of 2-needle manipulation	21.5±13.6μV	19.6±7.7μV	.71
	P value, before vs after	.946	.839
	% Change after treatment	4.02±37.43	0.03±1.90	.74
Wai-guan + Qu-chi	3 min after cessation of 2-needle manipulation	9.5±3.5μV	19.3±7.8μV	.002†
	P value, before vs after	.002†	.12
	% Change after treatment	–49.56±19.04	–2.23±3.90	4.22×10−7†

NOTE. Values are mean ± SD.

Comparing the 2 groups, the changes in the mean EPN amplitude after completion of needle manipulation in the acupuncture group were significantly larger than those of the sham-acupuncture group. However, the differences in the EPN changes at the initiation of (or during) needle manipulation were not significant between the 2 groups.

Correlation Between Changes in Pain Intensity and Changes in Mean Amplitude of EPN 

The correlation between changes in pain intensity and changes in EPN amplitude was based only on the data before and after completion of the treatment, because no data of pain intensity during the treatment were available for comparison. This correlation was significantly high (r=.685), and their respective changes are listed in table 4.

Table 4. Correlation Between Changes in Pain Intensity and Changes in Endplate Noise Amplitude

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Discussion 

Summary of Important Findings in This Study 

This study has demonstrated that acupuncture needling to distal acupuncture points can influence the subjective pain intensity and the objective change of the mean EPN amplitude in the MTrP region of the upper trapezius muscle if the needling procedure is similar to MTrP injection suggested by Hong.¹⁷, ²⁶ Both pain intensity and mean EPN amplitude decreased significantly after completion of the whole course of acupuncture therapy. There was a significant correlation between the changes in pain intensity and those in the mean EPN amplitude in the MTrP region. This study strongly supports the remote effectiveness of acupuncture therapy on the proximal pain.

EPN Amplitude and Irritability of MTrP 

Kuan et al²² reported a positive correlation between the prevalence of EPN in the MTrP region and the pain intensity of the MTrP. In this study, we found a positive correlation between the EPN amplitude changes and the changes in pain intensity. EPN is nonpropagated electrical potentials but not action potentials. It was a summation of many miniature endplate potentials. A miniature endplate potential can be recorded with a small-tip recording EMG needle, but not easily with a regular EMG needle. However, with a careful manipulation, EPN can be frequently recorded with a regular EMG needle. Simons and his associated researcher¹⁶, ¹⁸, ²⁰, ²¹ have confirmed that EPN is another characteristic of MTrP and that an MTrP is always found in the endplate zone of a skeletal muscle. It has been suggested that EPN in the MTrP region is probably related to the excessive leakage of acetylcholine in the nerve ending, and is related to the energy crisis in the taut band.²⁰, ²¹, ²⁸ When the acetylcholine leakage increases, both the EPN amplitude and the EPN prevalence in the MTrP region are also increased. An increase of acetylcholine leakage may cause worsening of energy crisis, with subsequent increase of ischemia-induced inflammatory reaction.²⁹ Therefore, the pain intensity may also be increased. This could be the rationale of the correlation between the pain intensity and EPN changes in the MTrP region. Simons³⁰, ³¹ has recently considered that both central (spinal cord mechanism) and peripheral (local inflammation) mechanism may be involved in the mechanism of MTrP.

In this study, a stable EPN recording with no changes in EPN amplitude during whole study course was required. The factors that can affect the EPN amplitude include the diameter of the recording needle tip, the distance between the endplate and the needle tip, type and size of the reference electrode, tissue impedance, and so forth. Therefore, even stable EPN tracings can have different amplitudes from person to person or from different recording sites on the same person. It is not reliable to compare the EPN amplitude in different persons with various degrees of pain intensity. However, when the needle is placed at a certain site without any movement, all other variables become stable. Therefore, the only reliable assessment is to compare the changes in pain intensity and changes in EPN amplitude at several time points in a continuous recording of EPN recorded from the same site without needle movement. Initially, the continuous EPN tracing should be recorded to confirm that constant amplitude is maintained. Then, various degrees of pain in the MTrP region can be elicited to observe the changes of the EPN amplitude in this continuous traction recorded from the same MTrP. Therefore, in our study, we compared the change of pain intensity and the change of EPN amplitude at the same recording site before and after the treatment, instead of the raw data of pain intensity and EPN amplitude.

Changes in EPN Amplitudes After Distal Needling 

Unpredictably, the EPN amplitude increased remarkably at the initiation of the manipulation on the acupuncture needle in some patients in this study. It is likely that the pain at the acupuncture site elicited by the needle manipulation may also be referred to the proximal MTrP region, similar to the mechanism of remote influence of MTrP needling.³² However, after the acupuncture treatment, many LTRs had been elicited and the pain in the acupuncture point decreased after a mechanism similar to MTrP injection or needling. Therefore, the pain intensity decreased and the ENP amplitude decreased gradually down to a level lower than that before treatment. One may speculate that the increase in EPN amplitude is a result of a generalized agitation caused by severe pain in the acupuncture site, similar to the “jumping response” (a sudden withdrawal of the body) during snapping palpation or needling to the MTrP region.¹⁶ In such a case, the muscle tension in the whole body, especially in the upper trapezius muscle, may also increase. However, we did not observe any motor unit action potential in the continuous EMG recording from the MTrP site.

Mechanism of Acupuncture for Pain Control 

The mechanism of local effects on the site of needling for the immediate relief of pain after acupuncture or dry needling has been considered to be mediated via a neural pathway¹⁰, ³³ because the biochemical reaction is far slower than the neural impulse. It has been suggested that a strong (high-pressure) stimulation from the needle tip to the nociceptor can cause a strong spinal cord reflex to break the vicious cycle of the MTrP circuit in the spinal cord.¹³, ¹⁴ Superficial dry needling has also been reported to be effective for pain relief.³³ However, clinically we hardly find any immediate effectiveness after superficial dry needling, including superficial acupuncture. It is possible that superficial needling induces slow changes in the pain circuit via different neural pathways.

Regarding the mechanism of remote acupuncture effects, it is probably similar to MTrP needling. Hsieh et al³² have demonstrated the remote effect of MTrP needling. It has been hypothesized that a strong mechanical stimulation can elicit a referred pain and a local twitch response and subsequently break the vicious cycle of MTrP circuits for the other remote MTrPs located in the same referred zone.³² In this study, the neural mechanism of the remote effect has been further supported. More study on the neural pathway is necessary to explore this mechanism.

One may speculate that the strong pain perception in the distal acupuncture site may interfere with the proximal portion of the body via a central neural pathway higher than the spinal cord, or even psychological factors. This may interfere with our interpretation of the spinal cord mechanism. However, the objective changes in EPN amplitude may exclude the possibility of a psychological effect.

Study Limitations 

The most critical limitation is the small sample size. The difficulty in patient selection is the major reason. Because the statistical analyses showed significant changes in both subjective and objective assessments compared with a control group, the information still can provide significant explanation for the remote acupuncture effect. The second critical problem in this study is the difficulty in pain intensity assessment on the proximal MTrP during the acupuncture on the remote sites. Third, the lack of long-term follow-up is a deficit in this study.

In the future, a similar study on a large sample with a better way to assess the pain intensity and a long-term follow-up is strongly suggested. It is also important to try needling on other acupuncture points in remote regions.

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Conclusion 

The remote effect of acupuncture has been demonstrated in this study. Both subjective change in the pain intensity and objective change of the EPN amplitude in the MTrP region of the upper trapezius muscle were found after dry needling of the remote ipsilateral acupuncture points. This could be a scientific basis for remote acupuncture effects.

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References 

1. Christensen BV, Iuhl IU, Vilbek H, Bulow HH, Dreijer NC, Rasmussen HF. Acupuncture treatment of severe knee osteoarthrosis: a long-term study. Acta Anaesthesiol Scand. 1992;36(6):519–525
   • View In Article
   • MEDLINE
   • CrossRef
2. Kalauokalani D, Sherman KJ, Cherkin DC. Acupuncture for chronic low back pain: diagnosis and treatment patterns among acupuncturists evaluating the same patient. South Med J. 2001;94:486–492
   • View In Article
   • MEDLINE
   • CrossRef
3. Kim DH. Evolution of acupuncture for pain management. Semin Integr Med. 2004;2:135–147
   • View In Article
4. Witt CM, Jena S, Brinkhaus B, Liecker B, Wegscheider K, Willich SN. Acupuncture for patients with chronic neck pain. Pain. 2006;125:98–106
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (151 KB)
   • CrossRef
5. Kennedy S, Baxter GD, Kerr DP, Bradbury I, Park J, McDonough SM. Acupuncture for acute non-specific low back pain: a pilot randomised non-penetrating sham controlled trial. Complement Ther Med. 2008;16:139–146
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (267 KB)
   • CrossRef
6. Ceccherelli F, Rigoni MT, Gagliardi G, Ruzzante L. Comparison of superficial and deep acupuncture in the treatment of lumbar myofascial pain: a double-blind randomized controlled study. Clin J Pain. 2002;18:149–153
   • View In Article
   • MEDLINE
   • CrossRef
7. Irnich D, Behrens N, Gleditsch JM, et al. Immediate effects of dry needling and acupuncture at distant points in chronic neck pain: results of a randomized, double-blind, sham-controlled crossover trial. Pain. 2002;99:83–89
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (106 KB)
   • CrossRef
8. He D, Veiersted KB, Hostmark AT, Medb JI. Effect of acupuncture treatment on chronic neck and shoulder pain in sedentary female workers: a 6-month and 3-year follow-up study. Pain. 2004;109:299–307
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (152 KB)
   • CrossRef
9. Itoh K, Katsumi Y, Hirota S, Kitakoji H. Randomised trial of trigger point acupuncture compared with other acupuncture for treatment of chronic neck pain. Complement Ther Med. 2007;15:172–179
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (362 KB)
   • CrossRef
10. Hong CZ. Myofascial trigger points: pathophysiology and correlation with acupuncture points. Acupunct Med. 2000;18:41–47
    • View In Article
    • CrossRef
11. Melzack R. Myofascial trigger points: relation to acupuncture and mechanisms of pain. Arch Phys Med Rehabil. 1981;62:114–117
    • View In Article
    • MEDLINE
12. Gunn CC. Treatment of chronic pain: intramuscular stimulation for myofascial pain of radiculopathic origin. London: Churchill Livingston; 1996;
    • View In Article
13. Hong CZ. Myofascial pain therapy. J Musculoskel Pain. 2004;12:37–43
    • View In Article
14. Hong CZ. Treatment of myofascial pain syndrome. Curr Pain Headache Rep. 2006;10:345–349
    • View In Article
    • MEDLINE
    • CrossRef
15. Travell JG, Simons DG. Myofascial pain and dysfunction: the trigger point manual. Baltimore: Williams & Wilkins; 1983;vol 1
    • View In Article
16. Simons DG, Travell JG, Simons LS. Myofascial pain and dysfunction: the trigger point manual. 2nd ed.. Baltimore: Williams & Wilkins; 1999;vol 1
    • View In Article
17. Hong CZ. Considerations and recommendations regarding myofascial trigger point injection. J Musculoskel Pain. 1994;2:29–59
    • View In Article
18. Hong CZ, Simons DG. Pathophysiologic and electrophysiologic mechanisms of myofascial trigger points. Arch Phys Med Rehabil. 1998;79:863–872
    • View In Article
    • Abstract
    • Full-Text PDF (1237 KB)
    • CrossRef
19. Hong CZ, Chen JT, Chen SM, Yan JJ, Su YJ. Histological findings of responsive loci in a myofascial trigger spot of rabbit skeletal muscle from where localized twitch responses could be elicited. Arch Phys Med Rehabil. 1996;77:962
    • View In Article
20. Simons DG, Hong CZ, Simons LS. Prevalence of spontaneous electrical activity at trigger spots and at control sites in rabbit skeletal muscle. J Musculoskel Pain. 1995;3:35–48
    • View In Article
21. Simons DG, Hong CZ, Simons LS. Endplate potentials are common to midfiber myofacial trigger points. Am J Phys Med Rehabil. 2002;81:212–222
    • View In Article
    • MEDLINE
    • CrossRef
22. Kuan TS, Hsieh YL, Chen SM, Chen JT, Yen WC, Hong CZ. The myofascial trigger point region: correlation between the degree of irritability and the prevalence of endplate noise. Am J Phys Med Rehabil. 2007;86:183–189
    • View In Article
    • MEDLINE
    • CrossRef
23. Gerwin RD, Shannon S, Hong CZ, Hubbard D, Gevirtz R. Interrater reliability in myofascial trigger point examination. Pain. 1997;69:65–73
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (141 KB)
    • CrossRef
24. Chou LW, Hong JY, Hong CZ. A new technique for acupuncture therapy and its effectiveness in treating fibromyalgia syndrome: a case report. J Musculoskel Pain. 2008;16:193–198
    • View In Article
25. Park J, White A, Stevinson C, Ernst E, James M. Validating a new non-penetrating sham acupuncture device: two randomised controlled trials. Acupunct Med. 2002;20:168–174
    • View In Article
    • MEDLINE
    • CrossRef
26. Hong CZ. Lidocaine injection versus dry needling to myofascial trigger point: the importance of the local twitch response. Am J Phys Med Rehabil. 1994;73:256–263
    • View In Article
    • MEDLINE
    • CrossRef
27. Chen JT, Chen SM, Kuan TS, Chung KC, Hong CZ. Phentolamine effect on the spontaneous electrical activity of active loci in a myofascial trigger spot of rabbit skeletal muscle. Arch Phys Med Rehabil. 1998;79:790–794
    • View In Article
    • Abstract
    • Full-Text PDF (646 KB)
    • CrossRef
28. Simons D, Travell J, Simons L. Myofascial pain and dysfunction: the trigger point manual. 2nd ed.. Baltimore: Williams & Wilkins; 1999;
    • View In Article
29. Shah JP, Danoff JV, Desai MJ, et al. Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points. Arch Phys Med Rehabil. 2008;89:16–23
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (557 KB)
    • CrossRef
30. Simons DG. Review of enigmatic MTrPs as a common cause of enigmatic musculoskeletal pain and dysfunction. J Electromyogr Kinesiol. 2004;14:95–107
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (291 KB)
    • CrossRef
31. Simons DG. New views of myofascial trigger points: etiology and diagnosis. Arch Phys Med Rehabil. 2008;89:157–159
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (67 KB)
    • CrossRef
32. Hsieh YL, Kao MJ, Kuan TS, Chen SM, Chen JT, Hong CZ. Dry needling to a key myofascial trigger point may reduce the irritability of satellite MTrPs. Am J Phys Med Rehabil. 2007;86:397–403
    • View In Article
    • MEDLINE
    • CrossRef
33. Baldry P. Superficial dry needling at myofascial trigger point sites. J Musculoskel Pain. 1995;3:117–126
    • View In Article

• a Neuro-EMG-Micro; Neurosoft, 5, Voronin Str, Ivanovo, Russia.
• b Statistical Package for the Social Sciences version 10.0 for Windows; SPSS Inc. Headquarters, 233 S. Wacker Dr, 11th Fl, Chicago, IL 60606.