Local Twitch Response Research Articles

Myofascial Pain Syndrome: Correlation between the Irritability of Trigger Points and the Prevalence of Local Twitch Responses during Trigger Point Injection

ObjectiveTo assess the correlation between the trigger point [TrP] irritability in the myofascial pain syndrome [MPS] and the prevalence of one or more local twitch responses [LTRs] during TrP injection.MethodsPatients with MPS, active TrPs in the trapezius muscle, and a pain intensity greater than 5 [numerical pain scale, 0 = no pain; 10 = worst pain in life] were recruited for this study. Pain intensity and pressure pain threshold [PPT] were measured before and immediately after TrP injection.ResultsA total of 72 MPS patients [30 males, 42 females] participated in this study. It was found that the pain intensity was significantly reduced [P < 0.05] and the PPT was significantly increased [P < 0.05] immediately after TrP injection.ConclusionsThis study supports the hypothesis that in MPS there are multiple sensitized loci nociceptors in TrP regions and that the Local Twitch Response is related to the irritability of the TrP.

Referred Pain From Myofascial Trigger Points in Head, Neck, Shoulder, and Arm Muscles Reproduces Pain Symptoms in Blue-collar (Manual) and White-collar (Office) Workers

To describe the prevalence and referred pain area of trigger points (TrPs) in blue-collar (manual) and white-collar (office) workers, and to analyze if the referred pain pattern elicited from TrPs completely reproduces the overall spontaneous pain pattern. Sixteen (62% women) blue-collar and 19 (75% women) white-collar workers were included in this study. TrPs in the temporalis, masseter, upper trapezius, sternocleidomastoid, splenius capitis, oblique capitis inferior, levator scapulae, scalene, pectoralis major, deltoid, infraspinatus, extensor carpi radialis brevis and longus, extensor digitorum communis, and supinator muscles were examined bilaterally (hyper-sensible tender spot within a palpable taut band, local twitch response with snapping palpation, and elicited referred pain pattern with palpation) by experienced assessors blinded to the participants' condition. TrPs were considered active when the local and referred pain reproduced any symptom and the patient recognized the pain as familiar. The referred pain areas were drawn on anatomic maps, digitized, and measured. Blue-collar workers had a mean of 6 (SD: 3) active and 10 (SD: 5) latent TrPs, whereas white-collar workers had a mean of 6 (SD: 4) active and 11 (SD: 6) latent TrPs (P>0.548). No significant differences in the distribution of active and latent TrPs in the analyzed muscles between groups were found. Active TrPs in the upper trapezius, infraspinatus, levator scapulae, and extensor carpi radialis brevis muscles were the most prevalent in both groups. Significant differences in referred pain areas between muscles (P<0.001) were found; pectoralis major, infraspinatus, upper trapezius, and scalene muscles showed the largest referred pain areas (P<0.01), whereas the temporalis, masseter, and splenius capitis muscles showed the smallest (P<0.05). The combination of the referred pain from TrPs reproduced the overall clinical pain area in all participants. Blue-collar and white-collar workers exhibited a similar number of TrPs in the upper quadrant musculature. The referred pain elicited by active TrPs reproduced the overall pain pattern. The distribution of TrPs was not significantly different between groups. Clinicians should examine for the presence of muscle TrPs in blue-collar and white-collar workers.

Muscle Trigger Points, Pressure Pain Threshold, and Cervical Range of Motion in Patients With High Level of Disability Related to Acute Whiplash Injury

Cross sectional cohort study. To analyze the differences in the prevalence of trigger points (TrPs) between patients with acute whiplash-associated disorders (WADs) and healthy controls, and to determine if widespread pressure hypersensitivity and reduced cervical range of motion are related to the presence of TrPs in patients with acute WADs. The relationship between active TrPs and central sensitization is not well understood in patients with acute WADs. Twenty individuals with a high level of disability related to acute WAD and 20 age- and sex-matched controls participated in the study. TrPs in the temporalis, masseter, upper trapezius, levator scapulae, sternocleidomastoid, suboccipital, and scalene muscles were examined. TrPs are defined as hypersensitive spots in a palpable taut band, producing a local twitch response and referred pain when palpated. Pressure pain threshold (PPT) was assessed bilaterally over the C5-6 zygapophyseal joints, second metacarpal, and tibialis anterior muscle. Active cervical range of motion, neck pain, and self-rated disability using the Neck Disability Index were also assessed. The mean ± SD number of TrPs for the patients with acute WAD was 7.3 ± 2.8 (3.4 ± 2.7 were latent TrPs; 3.9 ± 2.5 were active TrPs). In comparison, healthy controls had 1.7 ± 2.2 latent and no active TrPs (P<0.01). In patients with acute WAD, the most prevalent sites for active TrPs were the levator scapulae and upper trapezius muscles. The number of active TrPs increased with higher neck pain intensity (P<0.001) and a higher number of days since the accident (P=.003). Patients had significantly lower PPTs in all tested locations and less active cervical range of motion than controls (P<.001). In the patient group, there were significant negative correlations between the number of active TrPs and PPT over the C5-C6 joints and cervical range of motion in flexion, extension, and rotation in both directions: the greater the number of active TrPs, the lower the bilateral PPT over the neck and the greater the cervical range of motion limitation. The local and referred pain elicited from active TrPs reproduced neck and shoulder pain patterns in individuals with acute WADs with higher levels of disability. Patients with acute WADs exhibited widespread pressure hypersensitivity and reduced cervical mobility. The number of active TrPs was related to higher neck pain intensity, the number of days since the accident, higher pressure pain hypersensitivity over the cervical spine, and reduced active cervical range of motion.

Trigger Point Needling: Techniques and Outcome

In this review we provide the updates on last years' advancements in basic science, imaging methods, efficacy, and safety of dry needling of myofascial trigger points (MTrPs). The latest studies confirmed that dry needling is an effective and safe method for the treatment of MTrPs when provided by adequately trained physicians or physical therapists. Recent basic studies have confirmed that at the site of an active MTrP there are elevated levels of inflammatory mediators, known to be associated with persistent pain states and myofascial tenderness and that this local milieu changes with the occurrence of local twitch response. Two new modalities, sonoelastography and magnetic resonance elastography, were recently introduced allowing noninvasive imaging of MTrPs. MTrP dry needling, at least partially, involves supraspinal pain control via midbrain periaqueductal gray matter activation. A recent study demonstrated that distal muscle needling reduces proximal pain by means of the diffuse noxious inhibitory control. Therefore, in a patient too sensitive to be needled in the area of the primary pain source, the treatment can be initiated with distal needling.

Remote Therapeutic Effectiveness of Acupuncture in Treating Myofascial Trigger Point of the Upper Trapezius Muscle

This study aimed to investigate the remote effect of acupuncture (AcP) on the pain intensity and the irritability of the myofascial trigger point in the upper trapezius muscle. Forty-five patients were equally divided into three groups: patients in the placebo control group received sham AcP, those in the simple needling group were treated using simple needling, and those in the modified AcP received AcP with the rapid "screwed in and out" into multiple sites to elicit local twitch responses. The acupoints of Wai-guan and Qu-chi were treated. The outcome assessments included changes in subjective pain intensity, pressure pain threshold, range of motion, and mean amplitude of endplate noise in the myofascial trigger point region. Immediately after acupuncture, all measured parameters improved significantly in the simple needling and modified AcP groups, but not in the placebo control group. There were significantly larger changes in all parameters in the modified AcP group than that in the simple needling group. The myofascial trigger point irritability could be suppressed after a remote acupuncture treatment. It appears that needling to the remote AcP points with multiple needle insertions of modified AcP technique is a better technique than simple needling insertion of simple needling technique in terms of the decrease in pain intensity and prevalence of endplate noise and the increase in pressure pain threshold in the needling sites (represented either AcP points and or myofascial trigger points). We have further confirmed that the reduction in endplate noise showed good correlation with a decreased in pain.

Detecting Local Twitch Responses of Myofascial Trigger Points in the Lower-Back Muscles Using Ultrasonography

Rha D-w, Shin JC, Kim Y-K, Jung JH, Kim YU, Lee SC. Detecting local twitch responses of myofascial trigger points in the lower-back muscles using ultrasonography. Objective To evaluate the role of ultrasonography for detecting local twitch responses (LTRs) of myofascial trigger points (MTrPs) in deeply located lower-back muscles. Design Case-control study. Active MTrP was diagnosed in all patients based on the criteria proposed by Travell and Simons in their upper-trapezius or lower-back muscles. One investigator administered trigger point injections while observing LTRs on ultrasonography. The other investigator observed LTRs visually during the procedure. Setting University rehabilitation hospital. Participants Patients (n=41; mean age, 51.8±11.8y) with MTrPs in the upper-trapezius muscles and patients (n=62; mean age, 56.8±11.9y) with MTrPs in the erector spinae or quadratus lumborum were recruited from April 29 to October 31, 2010. Interventions Ultrasound-guided trigger point injection. Main Outcome Measures LTR detection rate according to the depth of MTrPs; subjective pain intensity using a visual analog scale before and immediately after the trigger point injection. Results In upper-trapezius muscles, all LTRs were detected by means of both ultrasonographic and visual inspection. In the lower-back muscles, many LTRs were detected only on ultrasonography during the trigger point injection. For deep muscles, ultrasound helped identify LTRs that were not detected by using visual assessment. Pain was alleviated more significantly in the group with LTRs during trigger point injections compared with the group without LTRs. Conclusions These findings suggest that ultrasonography was useful for detecting LTRs of MTrPs, especially for LTRs in the deep muscles. Ultrasound guidance may improve the therapeutic efficacy of trigger point injection for treating MTrPs in the deep muscles.

Latent Myofascial Trigger Points

A latent myofascial trigger point (MTP) is defined as a focus of hyperirritability in a muscle taut band that is clinically associated with local twitch response and tenderness and/or referred pain upon manual examination. Current evidence suggests that the temporal profile of the spontaneous electrical activity at an MTP is similar to focal muscle fiber contraction and/or muscle cramp potentials, which contribute significantly to the induction of local tenderness and pain and motor dysfunctions. This review highlights the potential mechanisms underlying the sensory-motor dysfunctions associated with latent MTPs and discusses the contribution of central sensitization associated with latent MTPs and the MTP network to the spatial propagation of pain and motor dysfunctions. Treating latent MTPs in patients with musculoskeletal pain may not only decrease pain sensitivity and improve motor functions, but also prevent latent MTPs from transforming into active MTPs, and hence, prevent the development of myofascial pain syndrome.

Anatomical substract of the trapezius muscle myofascial trigger points

Myofascial pain syndrome (MPS) is a common cause of chronic musculoskeletal pain and is characterized by myofascial trigger points(MTP), limited range of motion in joints, referred pain and local twitch response during mechanical stimulation of MTP. MTP are clinically identified by palpation of a taut band of muscle or fascia. Physiopathology of MPS remains unclear and it has been suggested that MTP occur when a nociceptor and a muscular motor endplate coincide. Seven different MTP are clinically described for the trapezius muscle, but anatomical correlation is still lacking. Trapezius muscles from two adult male cadavers were carefully dissected from their origins in order to observe the exact point where branches of the spinal accessory nerve entered the muscle belly. Four points were identified: (1) Mid portion of the superior margin, into the vertical fibers that reach the clavicle, (2) Caudal and lateral to the first point, located into the transverse fibers of the muscle; (3) Medial fibers near to the inferior margin of the muscle; (4) Central part of the muscle belly, between C7‐D3 levels. These locations correspond to the clinically described MTP. Anatomical correlation of the MTP may be useful for a better understanding of the physiopathology of these disorders and provide basis for their treatment.

Unterschiede zwischen myofazialen Triggerpunkten und „tender points“

The article describes and compares the characteristics of myofascial trigger points (MTrPs) of the myofascial pain syndrome and the tender points (TePs) of the fibromyalgia syndrome. Many statements are hypothetical, because not all aspects of the disorders have been clarified in solid studies. Signs and symptoms of MTrPs: (1) palpable nodule, often located close to the muscle belly, (2) often single, (3) allodynia and hyperalgesia at the MTrP, (4) referral of the MTrP pain, (5) normal pain sensitivity outside the MTrPs, (6) local twitch response, (7) local contracture in biopsy material, (8) peripheral mechanism probable. Signs and symptoms of TePs: (1) no palpable nodule, (2) location often close to the muscle attachments, (3) multiple by definition, (4) allodynia and hyperalgesia also outside the TePs, (5) enhanced pain under psychic stress, (6) unspecific histological changes in biopsy material, (7) central nervous mechanism probable. The multitude of differences speak against a common aetiology and pathophysiology.

Effect of Treatment on Trigger Points

Patients with muscle pain complaints commonly are seen by clinicians treating pain, especially pain of musculoskeletal origin. Myofascial trigger points merit special attention because its diagnosis requires examinations skills and its treatment requires specific techniques. If undiagnosed, the patients tend to be overinvestigated and undertreated, leading to chronic pain syndrome. Patients with myofascial pain syndrome present primarily with painful muscle(s) and restricted range of motion of the relevant joint. Palpable painful taut bands are named trigger points and are the main and pathognomonic finding on physical examination. Eliciting local twitch response and referred pain requires experience and examination skills. It may be useful to classify the patient as having acute or chronic, and as having primary or secondary, myofascial pain so the decision on the details of treatment can be curtailed to the needs of each patient. Effective treatment modalities are local heat and cold, stretching exercises, spray-and-stretch, needling, local injection, and high-power pain threshold ultrasound.

Asociación de puntos gatillo miofasciales en la cefalea tensional crónica y episódica

Objective To analyze the data from two of our studies in order to compare the association of myofascial trigger points (TrPs) in patients with chronic (CTTH) and frequent episodic tension type headache (ETTH). Material and methods Twenty-five patients with CTTH, 15 subjects with frequent ETTH, and 25 healthy controls (HC) were included. A headache diary was kept for 4 weeks to record the pain history. A blinded assessor examined all the participants in search for TrPs in the trapezius, sternocleidomastoid and temporalis muscles. TrPs were diagnosed according to the following criteria: 1, presence of a taut band within the muscle; 2, presence of a hypersensitive spot in the taut band; 3, local twitch response elicited by snapping palpation, and 4, referred pain elicited by palpation of the TrP. TrPs that evoked a familiar pain were considered active, and those that evoked a non-familiar pain were considered latent. Results Patients showed a greater number of myofascial TrPs compared to controls (F=33.44; P<0.001). The presence of latent TrPs was not significantly different between groups, but active muscle TrPs were only present in patients. The distribution of muscle TrPs (either active or latent) was similar in both groups of patients (0.45<OR<1.5). The total number of TrPs in the analyzed muscles did not show any relationship with the headache parameters. Conclusions Patients with CTTH and frequent ETTH show TrPs in the cranio-cervical muscles in a similar proportion. Tension-type headache may at least partly be explained by the referred pain originated in TrPs of the cranio-cervical muscles.

Current studies on myofascial pain syndrome

Recent studies have clarified the nature of myofascial trigger points (MTrPs). In an MTrP region, multiple hyperirritable loci can be found. The sensory components of the MTrP locus are sensitized nociceptors that are responsible for pain, referred pain, and local twitch responses. The motor components are dysfunctional endplates that are responsible for taut band formation as a result of excessive acetylcholine (ACh) leakage. The concentrations of pain- and inflammation-related substances are increased in the MTrP region. It has been hypothesized that excessive ACh release, sarcomere shortening, and release of sensitizing substances are three essential features that relate to one another in a positive feedback cycle. This MTrP circuit is the connection among spinal sensory (dorsal horn) neurons responsible for the MTrP phenomena. Recent studies suggest that measurement of biochemicals associated with pain and inflammation in the MTrP region, the sonographic study of MTrPs, and the magnetic resonance elastography for taut band image are potential tools for the diagnosis of MTrPs. Many methods have been used to treat myofascial pain, including laser therapy, shockwave therapy, and botulinum toxin type A injection.

538 MYOFASCIAL TRIGGER POINTS IN SUBJECTS WITH WHIPLASH SYNDROME: A PILOT STUDY

Background and Aim: It is suggested that muscle trigger points (TrPs) can be involved in the genesis of the pain in whiplash associated disorders (WAD). Since no previous study has systematically explored TrPs in WAD, our aim was to investigate in a blinded design the presence of TrPs in 7 pair of muscles in WAD patients compared to controls. Methods: Six male and 4 female (age: 30 ± 5 years) diagnosed with WAD grade II and 10 ageand sex-matched healthy controls (age: 31 ± 6 years) participated. TrPs in upper trapezius, sternocleidomastoid, suboccipital, levator scapulae, scalene, temporalis and masseter muscle were bilaterally explored following Simons et al criteria: hyperirritable spot in a palpable taut band, local twitch response elicited by snapping palpation and presence of referred pain. TrPs were active if the referred pain reproduced symptoms of the subject, and TrPs were latent when the referred pain did not reproduce symptoms. Results: The mean number of TrPs on each WAD subject was 4.8 (SD: 1.6) active TrPs and 2.5 (SD: 1.2) latent TrPs. Controls only exhibited latent TrPs (mean: 2.5; SD: 0.5). Significant difference between groups were found for active (P < 0.001), but not latent TrPs (P = 0.9). Active TrPs in the levator scapulae (n=9, n=9 right / left side), upper trapezius (n=6, n=5), and scalene (n=4, n=3) muscles were the most prevalent in WAD subjects. Conclusions: The referred pain elicited from active TrPs in head/neck muscles may be involved in the pathophysiology of WAD.

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.

The Effect of High-Power Pain Threshold Ultrasound Therapy on the Electrical Activity of Trigger Points and Local Twitch Response on Electromyography: A Preliminary Study

Objectives: We aimed to compare the effects of the high-power pain threshold ultrasound [HPPTUS] technique and needling on the spontaneous electrical activity [SEA] of trigger points [TrPs], local twitch response [LTR], and clinical improvement in myofascial pain syndrome.Methods: Twenty female patients presenting with acute TrPs on their upper trapezius muscles were included in this study. The patients were randomly assigned into two groups. The cases in the study group underwent HPPTUS technique and active stretching of the muscle. The cases in the control group underwent dry needling done by five adjacent electromyography [EMG] needle penetrations on the TrP [dry needling and analysis done concurrently] and did active stretching. Number of points where SEA observed were recorded. Visual analog scale [VAS], range of motion [ROM] measurement during contralateral flexion of the cervical spine, and the number of LTR were recorded.Results: Significant improvements were measured in both groups in terms of pa...

Active Muscle Trigger Points as Sign of Sensitization in Chronic Primary Headaches

Objective: To describe the differences in the presence of trigger points [TrPs] in neck and shoulder muscles that elicit referred pain to the head between nummular headache [NH], chronic tension-type headache [CTTH], and healthy controls [HNC].Methods: Ten NH [i.e., head pain exclusively felt in a small rounded or elliptical area of the head, not attributed to another disorder], 10 CTTH, and 10 HNC participated. The upper trapezius, sternocleidomastoid, and temporalis muscles were bilaterally examined by an assessor blinded to the subjects' condition for the presence of muscle TrPs as follows: hyperirritable spot within a taut band, local twitch response, and referred pain with palpation. TrPs were considered active if the referred pain reproduced the pattern and features of spontaneous headache attacks.Results: The number of TrPs was significantly higher [P < 0.001] in the CTTH group [mean: 4.4, standard deviation [SD]: 1.7] as compared to both NH [mean: 0.9, SD: 0.7] and HNC groups [mean: 1.2, SD: 0.6],...

Reliability of Physical Examination for Diagnosis of Myofascial Trigger Points

Trigger points are promoted as an important cause of musculoskeletal pain. There is no accepted reference standard for the diagnosis of trigger points, and data on the reliability of physical examination for trigger points are conflicting. To systematically review the literature on the reliability of physical examination for the diagnosis of trigger points. MEDLINE, EMBASE, and other sources were searched for articles reporting the reliability of physical examination for trigger points. Included studies were evaluated for their quality and applicability, and reliability estimates were extracted and reported. Nine studies were eligible for inclusion. None satisfied all quality and applicability criteria. No study specifically reported reliability for the identification of the location of active trigger points in the muscles of symptomatic participants. Reliability estimates varied widely for each diagnostic sign, for each muscle, and across each study. Reliability estimates were generally higher for subjective signs such as tenderness (kappa range, 0.22-1.0) and pain reproduction (kappa range, 0.57-1.00), and lower for objective signs such as the taut band (kappa range, -0.08-0.75) and local twitch response (kappa range, -0.05-0.57). No study to date has reported the reliability of trigger point diagnosis according to the currently proposed criteria. On the basis of the limited number of studies available, and significant problems with their design, reporting, statistical integrity, and clinical applicability, physical examination cannot currently be recommended as a reliable test for the diagnosis of trigger points. The reliability of trigger point diagnosis needs to be further investigated with studies of high quality that use current diagnostic criteria in clinically relevant patients.

Myofascial pain at post-sternotomy patients after cardiac surgery: A clinical study in 1226 patients

Background and objective: Sternotomy is a major type of surgery, and incidence, characteristics and clinical course of post-sternotomy pain are not well known. Myofascial pain also can occur according to sternotomy. So, the aim of this study was to investigate the incidence of myofascial pain and causative factors at post-sternotomy patients in different kind of cardiac surgeries. Methods: This study was performed between the years 2006-2007 at the Department of Cardiothoracic Surgery in Istanbul Kartal Kosuyolu Yuksek Ihtisas Hospital. 1226 patients over 18 years old were evaluated for myofascial pain. Trigger points in both upper trapezius, and both pectoralis major were identified according to Simons and Gerwin diagnostic criteria (tenderness in a hyper sensible spot within a palpable taut band, local twitch response elicited by snapping palpation, and elicited referred pain with palpation). Myofascial pain evaluation again was performed with the same pain physician at all examination periods. Results: When results were evaluated statistically, of the 1226 total patients, only in 194 (15.8%) patients trigger points were determined. When patients who were determined to have trigger points, it was observed that 135 had undergone CABG. These 135 patients were evaluated in 2 groups; those LIMA used and those where LIMA not used. In 102 patients who underwent CABG where LIMA were used (n = 102, 75.5%). Especially of those 194 patients majority suffered from the muscle groups in the left side more than in right side in terms of trigger point formation. Besides that we have determined a parallel relation between the operation duration and trigger point formation that was statistically significant. Conclusion: As a conclusion, the formation of trigger point in upper trapezius and pectoralis major muscles in patients going under CABG with LIMA is 31.9% in patients postoperatively. We believe the reason for this incident is the graft harvesting of the internal mammary artery. Besides we believe that there is a parallel relation between the operation duration and trigger point formation, and more prospective studies are needed to state the relation between the formation of trigger points and the duration of the CABG.

Evidence of neuroaxonal degeneration in myofascial pain syndrome: A study of neuromuscular jitter by axonal microstimulation

The mechanism of myofascial pain syndrome (MPS) is unclear. Previous reports pointed out that pathogenesis of either referred pain or local twitch response in trigger point of MPS is related to the nerve degeneration and disintegration of motor and sensory nerves in spinal cord. The purpose of the present study is to investigate the evidence of neuromuscular transmission disorders in trigger point muscles of patients with MPS by using stimulated single-fiber electromyography (SFEMG) examination. Twenty-three patients with neck MPS and 16 age-matched controls attended for the present study. The jitter or mean consecutive difference (MCD) was calculated as the mean of the absolute differences for 30 consecutive interpotential intervals between stimuli and single-fiber potentials in trapezius and levator scapulae muscles. The relationship between the MCD values and the disease duration was measured. The results showed significantly increased MCDs in trapezius and levator scapulae muscles in MPS patients. MCD values measured in the trigger point muscles were found to be positively correlated with the disease duration. The present study with axonal microstimulation and SFEMG demonstrates a prominent evidence of neuroaxonal degeneration and neuromuscular transmission disorders in the trigger point muscles of MPS patients. The mechanism of MPS is possibly implicated with the degeneration of motor neurons.

Topographical mapping and mechanical pain sensitivity of myofascial trigger points in the infraspinatus muscle

Objectives To screen for the presence of latent and active myofascial trigger points (MTrPs) in patients with unilateral shoulder and arm pain and perform topographical mapping of mechanical pain sensitivity bilaterally in the infraspinatus muscles. Methods Nineteen patients with unilateral musculoskeletal shoulder pain participated in the study. The area overlying the infraspinatus on each side was divided into 10 adjacent sub-areas of 1 cm 2, corresponding to the area of a pressure algometer probe. Pressure pain threshold (PPT) was measured in each sub-area bilaterally in the infraspinatus muscles. Following PPT measurement, an acupuncture needle was inserted into each sub-area five times in different directions in order to induce local twitch response and/or referred pain. Results A significantly lower PPT level in the infraspinatus muscle was detected on the painful side compared with the non-painful side ( P = 0.001). PPT at midfiber region of the infraspinatus muscles was lower than that at other muscle parts ( P < 0.05). Multiple, but not single, active MTrPs were found in the infraspinatus muscle on the painful side and there were also multiple latent MTrPs bilaterally in the infraspinatus muscles. PPT at active MTrPs was much lower than the latent MTrPs and again lower than the non-MTrPs. Conclusions There exists bilateral mechanical hyperalgesia in patients with unilateral shoulder pain. Further, the association of multiple active MTrPs with unilateral shoulder pain and the heterogeneity of mechanical pain sensitivity distribution suggest a crucial role of peripheral sensitization in chronic myofascial pain conditions. Additionally, the locations of MTrPs identified with dry needling correspond well to PPT topographical mapping, suggesting that dry needling and PPT topographical mapping are sensitive techniques in the identification of MTrPs.