Endplate Noise Research Articles

Dose-dependent and Ceiling Effects of Therapeutic Laser on Myofascial Trigger Spots in Rabbit Skeletal Muscles

ABSTRACTObjective: To evaluate the effect of low-level laser treatment with different dosages on the irritability of myofascial trigger spots [MTrS] in rabbit skeletal muscles.Methods: Twenty rabbits were equally divided into a low dose group and a high dose group. In each rabbit, the MTrS on the experimental side was irradiated with 660-nm continuous-wave gallium-aluminum-arsenate laser daily for six sessions. The energy per session was 27 J/cm2 [low dose group] and 72 J/cm2 [high dose group]. The MTrS on the other side received sham treatment. The MTrS irritability was assessed with the prevalence of endplate noise [EPN] at baseline after the first and after the last treatments.Results: After the first laser treatment, the EPN prevalence was significantly decreased in both groups. The percentage change in the high dose group was greater than that in the low dose group. The EPN prevalence after the last laser treatment was lower than that after the first laser treatment in the low dose group, but not in ...

Injection in the Cervical Facet Joint for Shoulder Pain With Myofascial Trigger Points in the Upper Trapezius Muscle

The goal of this double-blinded, randomized, controlled study was to confirm the effectiveness of the cervical facet joint injection in treating shoulder pain with the myofascial trigger point in the upper trapezius muscle secondary to cervical facet lesion. Eighty-nine patients with chronic unilateral shoulder pain due to myofascial trigger points in the upper trapezius muscle received an injection to the C4-5 facet joint in the experimental group and to the corresponding unilateral multifidi muscle in the control group. Subjective pain intensity and pressure pain threshold of the myofascial trigger point were assessed, and the prevalence of endplate noise in the myofascial trigger point region was measured in 28 patients before, immediately after, and 1 month after the injection. Half of the patients in the experimental group, but none of the control patients, reported being completely pain free 1 month after the injection. Both the decrease in the pain intensity and the increase in pressure pain threshold were significantly more in the experimental group than in the control group either immediately or 1 month after the injection. There was no significant difference in the change of endplate noise prevalence between the 2 groups. This study demonstrates that intra-articular or peri-articular injection into the cervical facet joint region can effectively inactivate the upper trapezius myofascial trigger point secondary to the facet lesion.

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

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.

Electrophysiologic Effects of a Therapeutic Laser on Myofascial Trigger Spots of Rabbit Skeletal Muscles

To better understand the mechanisms of therapeutic lasers for treating human myofascial trigger points, we designed a blinded controlled study of the effects of a therapeutic laser on the prevalence of endplate noise (EPN) recorded from the myofascial trigger spot (MTrS) of rabbit skeletal muscle. In eight rabbits, one MTrS in each biceps femoris muscle was irradiated with a 660-nm, continuous-wave, gallium-aluminum-arsenate (GaAlAs) laser, at 9 J/cm2. The contralateral side of muscle was treated with a sham laser. Each rabbit received six treatments. The immediate and cumulative effects were assessed by the prevalence of EPN with electromyographic (EMG) recordings after the first and last treatments. Compared with pretreatment values, the percentages of EPN prevalence in the experimental side after the first and last treatments were significantly reduced (P < 0.01 for both). The change in EPN prevalence in the experimental side was significantly greater than in the control side immediately after the first and last treatments (P < 0.05). However, no significant differences were noted between the first and last treatments (P > 0.05). In our study, immediate and cumulative effects of a GaAlAs laser applied on MTrS were demonstrated on the basis of the assessment of EPN prevalence. It seems that laser irradiation may inhibit the irritability of an MTrS in rabbit skeletal muscle. This effect may be a possible mechanism for myofascial pain relief with laser therapy.

Re: The Myofascial Trigger Point Region: Correlation Between the Degree of Irritability and the Prevalence of Endplate Noise

Shah, Jay P. MD; Parikh, Sagar MS IV; Danoff, Jerome PT, PhD; Gerber, Lynn H. MD Author Information

The Myofascial Trigger Point Region

This study was designed to investigate the correlation between the irritability of the myofascial trigger point (MTrP) and the prevalence of endplate noise (EPN) in the MTrP region of human skeletal muscle. Twenty normal subjects with latent MTrPs and 12 patients with active MTrPs in the upper trapezius muscles were recruited for this study. The patients reported the subjective pain intensity of the active MTrP (0-10). The MTrP and an adjacent non-MTrP site were confirmed and marked for the measurement of pressure pain threshold (with a pressure algometer) and the prevalence of EPN (with electromyographic recordings). The prevalence of EPN in the MTrP regions was significantly higher (P < 0.01) in the active MTrPs than in the latent ones. However, no EPN could be found in the non-MTrP region near either the active or the latent MTrPs. The pain intensity and the pressure pain threshold were highly correlated with the prevalence of EPN in the MTrP region (r = 0.742 and -0.716, respectively). The irritability of an MTrP is highly correlated with the prevalence of EPN in the MTrP region of the upper trapezius muscle. The assessment of EPN prevalence in an MTrP region may be applied to evaluate the irritability of that MTrP.

The spinal cord connections of the myofascial trigger spots

Background Recent electrophysiological studies revealed that endplate noise (EPN) could be specifically recorded from a myofascial trigger point (MTrP) region. EPN has been considered as the focal graded potentials due to excessive acetylcholine release in neuromuscular junction. A recent histological study has demonstrated a free nerve ending at the vicinity of the site, from where EPN could be recorded in an MTrP region. However, the sensory (afferent) and the motor (efferent) connections between an MTrP and the spinal cord still has never been fully studied. Aims The aim of this study was to delineate both motor and sensory connections between an MTrP and the spinal cord by applying the stain with horseradish peroxidase (HRP). Methods Nine Wistar rats were studied. When the rat was anesthetized, its biceps femoris muscles were exposed for localizing the myofascial trigger spot (MTrS, equivalent to MTrP in human). In one side, a monopolar Teflon-coated, hollow-needle electrode was used for searching EPN in an MTrS region, and then HRP was injected via this hollow-needle electrode into the site where EPN was recorded. HRP was also injected into a normal (non-taut band, non-MTrS) site in the contralateral side to obtain the control data. Two days after HRP injection, the rats were sacrificed and their spinal cords and dorsal root ganglia (DRG) were sectioned for the identification of the sites where neurons were labeled with HRP. Results The HRP-labeled neurons were found in the ventral horn of the spinal cord and in the DRG over L3, L4, and L5, while most were found in the L5 level. The mean numbers of HRP-labeled neurons in the EPN side looked smaller than that in the control side, but the difference did not reach statistically significant level ( P > 0.05). The mean values of the diameters of the HRP-labeled neurons in the DRG were not significantly different between the EPN side and the control side ( P > 0.05). However, HRP-neurons in the ventral horn of the spinal cord in the EPN side showed mild tendency to be smaller than that in the control side. Conclusions The spinal cord connections of an MTrS are basically similar to that for a normal tissue region. The motor neurons related to MTrS tended to be smaller in their diameters. The findings in this study further supported the previously proposed hypotheses for the pathogenesis of an MTrP.

Electrophysiological Assessment of Acupuncture Points

This study was designed to assess the occurrence of end plate noise (EPN) in an acupuncture point (AcP). Ten male and 10 female normal volunteers were included in this study. For each subject, mapping of the distribution of EPN loci in an AcP region of Stomach-36 in one leg selected randomly, and also in a nearby non-AcP region in the other leg as a control, was performed with electromyographic recordings. There were significantly more EPN loci in the AcP region of Stomach-36 than in the non-AcP region near this AcP. Whenever the searching needle approached an EPN locus, the subjects always felt pain, soreness, or an unpleasant sensation. This feeling was rarely reported when no EPN was recorded from any site in either an AcP region or a non-AcP region. After electromyographic study, every AcP was confirmed as a myofascial trigger point. Similar to the distribution of EPN loci in an MTrP region, significantly more EPN loci can be identified in an AcP region of Stomach-36 than in a nearby non-AcP site. This study provides additional support to the hypothesis that some AcPs are also myofascial trigger points.

An expansion of Simons’ integrated hypothesis of trigger point formation

Simons' integrated hypothesis proposed a model of trigger point (TrP) activation to explain known TrP phenomena, particularly endplate noise. We propose an expansion of this hypothesis to account for new experimental data and established muscle pathophysiology.

New Aspects of Myofascial Trigger Points: Etiological and Clinical

SUMMARYObjectives: To identify important new developments in our understanding of the nature and clinical characteristics of myofascial trigger points [TrPs].Findings: Recent research studies reinforce the credibility of three key features of an integrated hypothesis that is designed to explain the pathophysiology of TrPs: increased acetylcholine effect, increased muscle-fiber tension, and local release of sensitizing substances. Electromyographic studies of TrPs support an increased acetylcholine effect that produces endplate noise. Nine histological studies of animal and human subjects identify features that indicate abnormally increased muscle-fiber tension and help to account for the taut bands observed clinically. Microdialysis studies by Jay Shah, MD and colleagues at the National Institutes of Health compared, in nine subjects, the findings in active TrPs to findings in latent TrPs and in normal muscles [nine examinations]. They found a significantly reduced pressure pain threshold and pH at the th...

Diagnosis and therapy of myofascial trigger points

Myofascial trigger points (MTrPs) are hyperirritable tender spots in palpable tense bands of skeletal muscle. Muscle is an orphan organ, no medical specialty claims muscle as its organ. The article aims at filling some of the gaps in the current knowledge of MTrPs. The presented findings were partly obtained in experiments on anesthetised rabbits, partly they are the result of ample experience with patients suffering from MTrPs. Each muscle has a characteristic elicited referred pain pattern that, for active MTrPs, is familiar to the patient. Without a laboratory test or imaging method, diagnosis of MTrPs depends entirely on history and physical examination. MTrP symptoms follow muscle overload, are activated acutely by sudden overload, or develop gradually with prolonged contractions or repetitive activity. The diagnostic skill required depends on considerable innate palpation ability, authoritative training, and extensive clinical experience. Effective treatment methods include manual stretching by trigger-point pressure release, contract-relax, vapo coolant spray-and-stretch, and dry needling or injection of MTrPs. The integrated hypothesis presents an explanation for the pathophysiology of MTrPs and begins with excessive release of acetylcholine from involved motor endplates. It depends on a new understanding of the abnormality of endplate noise. Biopsies demonstrate segmental shortening of groups of sarcomeres in individual muscle fibres and possibly waves of contracted sarcomeres to account for palpable taut bands.

In vivo analysis of end-plate noise of human extensor digitorum brevis muscle after intramuscularly injected botulinum toxin type A.

To evaluate changes occurring in the neuromuscular junction after injection with botulinum neurotoxin type A (BoTx), three healthy volunteers were injected with 10 U BoTx in the right extensor digitorum brevis muscle. In agreement with previous observations, amplitude of compound muscle action potential (CMAP) decreased to approximately 30% of the initial value at approximately day 8 and slowly returned to baseline values around day 250. Values of the acetylcholine receptor (AChR) open time were determined by spectral analysis of end-plate noise and from single exponential fits to the decay phase of individual miniature end-plate potentials (MEPPs). At baseline, the mean channel open times determined by end-plate noise analysis and the exponential fits were 1.1 +/- 0.2 ms and 1.20 +/- 0.04 ms, respectively. After BoTx injection, initially no end-plate noise could be recorded. From day 9 onwards, however, a gradual recurrence of end-plate noise was observed, with mean channel open times of approximately 2-5 ms, being maximal between days 20 to 140. In addition, the shape of many recorded MEPPs was different from the typical fast rising MEPPs observed at baseline. After day 80, end-plate noise gradually returned to normal and mean channel open times decreased slowly to baseline values. Our findings reflect the changed AChR characteristics of newly formed neuromuscular junctions, which are created after BoTx injection and gradually removed after restoration of the original neuromuscular junctions.

Do endplate noise and spikes arise from normal motor endplates?

The concept that the endplate noise and endplate spike components of motor endplate potentials represent normal endplate potentials seems to be flawed. The morphology of the normal miniature endplate potentials described in the physiology literature is different from the morphology of the noise-like component of endplate potentials. This noise-like component is identified as normal in current electromyographic literature. There is strong experimental evidence that one source of the endplate noise component is grossly increased release (up to three orders of magnitude) of acetylcholine from the nerve terminal of that neuromuscular junction. The spikes can be accounted for by release of additional acetylcholine in response to mechanical stimulation by the electromyographic needle. Other possibilities exist.

Spontaneous Needle Electromyographic Activity in Myofascial Trigger Points in the Infraspinatus Muscle: A Blinded Assessment

Objective: Myofascial pain syndromes associated with trigger points [TrPs] are an established clinical entity but the structural and functional abnormalities of TrPs are not well under stood. The aim of the study was to conduct a blinded electromyographic investigation of TrPs.Methods: Nineteen young subjects with chronic shoulder and arm pain, who had a TrP [i.e., a tender point with referred pain, producing at least some of the pain complaint] in the infraspinatus muscle, were examined. This point and a nontender control point in the same muscle were code-marked, in order to blind the examiner. Around both points 20 concentric needle electromyographic [EMG] recordings were obtained at rest.Results: More subjects had spontaneous EMG activity at the TrPs than at the control point. The EMG activity was interpreted as end-plate noise or spikes or both. The TrP Root Mean Square amplitudes were significantly higher than at the control points.Conclusion: Our investigation has demonstrated the presence of spont...

End-plate electromyography: use of spectral analysis of end-plate noise.

An automated technique for estimating the channel open time of human end-plate acetylcholine receptors (AChR) is described. The method, which is based on the power spectral analysis of electromyographic end-plate noise, is simple and permits a rapid estimation of the dominant AChR ion channel kinetics. Values of AChR channel open time determined by spectral analysis of end-plate noise in adults (1.23 +/- 0.01 ms at 33 degrees C) were consistently shorter than those estimated from the decay phase of extracellularly recorded miniature end-plate potentials. The channel open time extracted from the end-plate noise compared well with that derived from the analysis of in vitro recorded acetylcholine-induced current noise. Therefore, spectral analysis of end-plate noise may provide a good estimation of the kinetics of the human AChR ion channel. The technique is particularly useful in identifying congenital myasthenic syndromes with altered AChR ion channel function.

Neuromuscular Transmission in experimental autoimmune myasthenia gravis (EAMG). Quantitative ionophoresis and current fluctuation analysis at normal and myasthenic rat end-plates.

Chronic experimental autoimmune myasthenia gravis (EAMG) was induced in rats by immunization with acetylcholine receptor (AChR) purified from the electroplax of Torpedo californica. 35--40 days after immunization, serum anti-AChR antibody titers were about 40 nM. At this stage, electrophysiology was performed on isolated M. omohyoideus muscle-preparations from myasthenic and from normal (control) rats. For the study of the equilibrium interaction between acetylcholine (ACh) and AChR, dose-response curves were obtained by quantitative ionophoretic application of ACh to voltage-clamped end-plates. Analysis of dose-response curves yielded the following parameters: maximum end-plate conductance per unit surface gmax (EAMG) = 10.3 +/- 1.1 nS/micrometer 2, gmax (normal) = 20.2 +/- 1.8 nS/micrometer 2; apparent dissociation constant K (EAMG) = 96 +/- 5 microM, K (normal) = 58 +/- 6 microM; Hill-coefficient nH (EAMG) = 2.3 +/- 0.1, nH (normal) = 2.3 +/- 0.1. Single channel properties were derived from an analysis of ACh-induced end-plate current noise: the mean single channel conductance was gamma (EAMG) = 20.1 +/- 2.2 pS, gamma (normal) = 27.6 +/- 1.8 pS and the mean channel life-time tau (EAMG) = 1.39 +/- 0.09 ms, tau (normal) = 1.32 +/- 0.08 ms (T = 22 degrees C). The electrophysiological data are interpreted as follows: (1) At myasthenic end-plates there is a 50--60% reduction of functioning AChR (decrease of gmax). A total number of about 2 x 10(6) (1 x 10(6)) channels per end-plate was calculated for control (myasthenic) rats. (2) The affinity of AChR for ACh is reduced and/or there is an impediment of the conformational change from the closed- to the open-channel configuration (increase of K). (3) Single channel properties are essentially unaffected.

Some Studies of the Clinical Neurophysiology of Denervation in the Dog

Muscles from 50 dogs were examined at various times after denervation. Electromyography (EMG) studies were made and motor nerve conduction velocities (NCV) measured. In partial denervation a reduced interference pattern was demonstrated in certain cases. In one case, which resembled spinal muscular atrophy in humans, giant motor unit potentials were present. Iii normal relaxed muscle, spontaneous activity was only recorded from the end plate zone. This ‘end plate noise’ was abolished by muscle relaxants. In denervated muscle, fibrillations and positive sharp waves were present in increasing numbers 5-7 days after denervation. After a total nerve lesion the NCV in the distal segment remained normal for 5-7 days when conduction ceased. The evoked muscle action potential decreased in amplitude during this period. These findings and their physiological origins arc discussed.

The characteristics of 'end-plate noise' produced by different depolarizing drugs.

1. End-plate depolarization and associated ;membrane noise' due to decamethonium, acetylthiocholine and suberyldicholine have been examined and compared with the effects of acetylcholine and carbachol.2. The transient ionic channels resulting from the action of decamethonium and acetylthiocholine are of much shorter duration than those produced by acetylcholine. They are, therefore, similarly to carbachol channels, less effective in causing membrane depolarization.3. Suberyldicholine, on the other hand, produces ion channels whose duration exceeds that of acetylcholine.4. Lowering the temperature causes an increase in amplitude of the elementary potential change produced by decamethonium and acetylthiocholine.5. The relation between the characteristic features of drug-induced membrane noise and the underlying molecular reaction rates is discussed.

"End-plate noise" in electromyography.

"End-plate noise" in electromyography.

Spontaneous electrical activity of human muscle

The spontaneous electrical activity of human muscle was studied in 197 normals, 67 patients with peripheral nerve involvement and 29 patients with progressive muscular dystrophy. “Noise” was observed in the end-plate zones of normal muscle; after minute displacements of the electrode the noise could be seen to consist of randomly occurring purely negative discharges 0.5–2 msec in duration and up to 100 μV in amplitude. This activity probably represents extracellularly recorded miniature end-plate potentials. Outside the end-plate zones of normal muscle a single site was rarely encountered yielding a spontaneous discharge similar to the fibrillation potentials of denervated muscle. In normal muscle such a discharge may correspond to the propagated disphasic potentials superimposed on the “end-plate noise”. The fibrillation potentials in patients with lower motor neurone disease were found to have longer durations than usually stated (1–5 msec as compared with 0.5–2 msec), a significant proportion of triphasic potentials (30%) and voltages half of which were of the same order (100–300 μV) as those of motor unit potentials. The fibrillations found in 29 of 76 patients with progressive muscular dystrophy had the same average duration, amplitude and shape as in denervated muscles. The fibrillation potentials were initiated in the end-plate zone as evidenced by the initial negative deflection of the potential recorded there and the initial positive deflection outside the end-plate zone. The initiation of the fibrillation potentials cannot be ascribed to mechanical stimulation by the intramuscular needle electrode since fibrillation potentials could also be recorded subcutaneously. With the 50 μ diameter leads of a multi-electrode fibrillation potentials were recorded with peak-to-peak amplitudes as high as 8.5 mV. The decline in amplitude along the multi-lead electrode was the same for fibrillation potentials 1 mV or more in amplitude as for the spike components of motor unit potentials, the voltage falling to less than one-tenth of maximum within 0.45 mm. This suggests that “high voltage” fibrillation potentials represent the spontaneous discharge of a sub-unit. The amplitudes of 100–600 μV fibrillation potentials declined relatively less with distance, suggesting that they were recorded farther away from the generators (about 0.5 mm) than the high voltage potentials. The small amplitude and rapid attenuation of positive sharp waves suggest that they are derived from a single muscle fibre. Cross talk in our multi-lead electrodes was insignificant and cannot explain the discrepancy between our findings and those of other investigators with regard to the voltage decline of spike potentials. The cause of fibrillation potentials is discussed in the light of the present knowledge of the properties of the membrane of denervated muscle fibres.