Local Twitch Response in the Myofascial Pain Syndrome

The clinical features of the myofascial pain syndrome [MPS] were recently reviewed (1). Clinician members of the American Pain Society, who regularly treat pain, were surveyed about the validity of the MPS diagnosis (2). From a sample of 403 responders, 88.5 percent considered the MPS to be a valid clinical disorder and 81 percent believed that it was different from the fibromyalgia syndrome [FMS]. In their opinion, the minimal criteria for diagnosis of MPS were a regional distribution of the symptoms and signs, the presence of trigger points [TrPs], and a normal neurological examination. The reader will recognize that local twitch response [LTR] was not among this short list of minimal criteria.

By contrast, one of the most comprehensive presentations of MPS diagnostic criteria (3) includes each of the following: regional body pain and stiffness, limited range of motion of the affected muscle, a LTR producing a taut band, one or more TrPs, referral [triggering] pain from a TrP to a zone of reference, and resolution of the symptoms with local anesthesia of the TrP.

A major problem for MPS in the clinical and scientific community has been that there are no universally accepted clinical criteria for the diagnosis of MPS, as have existed for FMS over the past 20 years (4–6). Several studies designed to evaluate the interrater reliability of clinical criteria for the diagnosis of MPS have failed (5,6), but at least two have succeded (5,7). It is time for the community of MPS experts to get together and establish criteria that can be widely accepted.

There is increasing evidence to suggest that the underlying pathophysiology of TrPs may involve a dysfunctional neuromuscular end plate (8), but an alternative mechanism involving the muscle spindle has been proposed (9). Perhaps both participate in a localized dysfunctional reflex arc as evidenced by an animal [rabbit] model of a TrP, the so-called trigger spon (10). In that study, transection of the relevant radicular nerve permanently obliterated the LTR associated with a given trigger spon, but cranialward transection of the cervical spinal cord did so only temporarily.

There is some intriguing objective data regarding the pathogenesis of the MPS. Ultrasound imaging techniques have been used to distinguish the TrPs of MPS from normal tissue lacking TrPs (11). Adaptations of this methodology have enabled investigators to visualize not only the stiffened muscular tissue in the TrP, but also to show that the affected muscle tissue resists blood flow into it (11). Other studies from the same group have used microdialysis to show that the microenvironment of the TrP is more acidic [think ischemic with release of lactic acid from anaerobic glycolysis] than normal tissue. In addition, it contains increased concentrations of inflammatory and neuroactive chemicals, such as bradykinin, calcitonin gene-related peptide, substance P, tumor necrosis factor-alpha, interleukin-1-beta, serotonin, and norepinephrine (12). It has been proposed that these changes result from local muscle ischemia which prompts local release of inflammatory substances that may sensitize muscle nociceptors (13,14).

Recent clinical studies have indicated that the LTR is sufficiently important to merit its inclusion in the diagnostic criteria of MPS associated with chronic tension headache (15) and to evaluate its role in the myofascial pain dysfunction syndrome [MPDS] involving the muscles of mastication (16). Electromyography performed with the recording needle in a taut band near a TrP detected the LTRs irrespective of whether they were induced by tapping or by needling the TrP (17), while surface EMG for this purpose is less reliable in some hands (17,18).

The lead article for this issue of the Journal of Musculoskeletal Pain [JMP] comes from Tainan, Miao-Li City and Tai-Chung, Taiwan (19). The authors recruited 72 MPS patients who had active TrPs in a trapezius muscle, and moderately severe pain from that source, to evaluate what they referred to as TrP irritability. By irritability, they meant that stimulation with a treatment needle would initiate a LTR. The TrP injection was carried out using a grid as a guide to placement of 25 needle penetrations and injections in the TrP. The grid was 5 mm on each side and containing 25 one millimeter squares to represent specific needle targets in the TrP area. Pain intensity and pressure pain threshold [PPT] were measured before and immediately after TrP injection. The frequency with which a TrP penetration produced a LTR was recorded. As the reader peruses this article, he/she would notice the effect of the injection procedure on the subjective pain severity, the PPT, and the prevalence of LTR. The authors also provide correlations that can help the reader predict the LTR prevalence based on the subjective pain intensity and the PPT.

The second research contribution to this issue comes from Ankara, Turkey (20). The authors clinically observed that some patients with cervical MPS exhibited a unique fear of falling and proposed to determine how common that fear might be in these patients. Fear of falling was evaluated using a Falls Efficacy Scale. Other outcome measures included a visual analog scale for subjective pain severity, functional reach, Berg Balance Test, the Beck Depression Inventory, and the Dizziness Handicap Inventory. The authors report their findings from these measures and what they predict regarding the probable mechanisms responsible for the fear of falling in these patients.

A study reported from Nijmegen, The Netherlands and Liverpool, United Kingdom (21) evaluated skeletal muscle function in patients with repetitive strain injury syndrome involving the upper extremities. Local oxygen consumption of the forearm muscles was examined at baseline and after exercise using near-infrared spectroscopy. As a comparator, the contractile properties of a quadriceps muscle were examined using isometric contractions and electrical stimulations. Since the potential political and epidemiological implications of these authors' findings are substantial, an expert in the field was invited to offer comment [see the invited Editorial to follow (22).]

A report regarding the potential benefits of exercise among elderly individuals with musculoskeletal pain has been obtained from Sao Paulo, Brazil (23). This is an uncontrolled prospective longitudinal study that enrolled subjects with musculoskeletal pain who were already voluntarily participating in the Young Men's Christian Association's elderly exercise program. Outcome assessments included a visual analog scale for subjective pain intensity, the Health Assessment Questionnaire, and the “Medical Outcome Study Short Form-36 Health Survey,” all translated into Portuguese and validated in Brazil. The outcomes of the study are reported and discussed. They probably are translatable to other regions of the world.

Continuing with the topic of musculoskeletal pain, investigators from Croatia reported their experience with a pain clinic in Split, Croatia (24). They proposed to study the composition and efficacy of a tertiary care pain clinic over a four-year period to gain understanding regarding the regional needs for pain management. They professed surprise to learn that chronic back pain was the most common condition being treated. They discussed, in considerable detail, the pharmacologic and non-pharmacologic therapies being used and proposed new directions for this program.

A report about management of neck pain comes from Bolu and Istanbul, Turkey (25). This study was designed to compare the efficacy of three manual medicine interventions for neck pain patients. Sixty patients with neck pain were randomized into three groups to evaluate the relative benefits of classical therapy versus classical therapy plus mobilization or classical therapy plus application of Kinesio tape to the neck. The reader will learn whether the classical therapy was enhanced by either mobilization or Kinesio tape application.

Again on the topic of neck pain comes a report by investigators from Tan Tock Seng, Singapore and from Nijmegen, The Netherlands (26). The study was designed to evaluate chronic idiopathic unilateral neck pain by a battery of discriminatory tests. The authors refer to this battery of tests as their comprehensive, multi-modal quantitative sensory testing [QST] protocol. Their QST protocol consists of PPT testing, thermal threshold testing, electrical pain threshold testing, wind-up response testing using electrical stimulation, and measurement of descending inhibitory modulation using the conditioned pain modulation paradigm. Before initiating this study, the authors already had an extensive database from earlier study of 118 healthy normal controls by this protocol. Eligible patients for this study were to have experienced unilateral chronic idiopathic neck pain for more than six months. Data representing demographically matched normal controls were drawn from the preexisting QST database. The reader will be interested to learn how long it took to find 18 ideal patients for this study and how the QST protocol data from these patients were different from that of the controls data. Even more revealing is what can be deduced from interpreting the study results because it helped the investigators to better understand the pathophysiology of this condition.

Finally, authors from Adana and Ankara Turkey report their experience with a comparison of gabapentin and pregabalin for the treatment of military veterans suffering from neuropathic pain due to combat-related peripheral nerve injury (27). Understandably, this is a pilot study seeking data to power a larger investigation on this topic. The dosages of the comparison drugs and the duration of this trial were appropriate. The focus of outcomes assessment was on pain, so both a pain visual analog scale and the Leeds Assessment of Neuropathic Symptoms and Signs pain scale were administered. In addition, the authors provide information derived from the Sleep Interference Score in their study participants. The reader will learn whether one of the studied drugs provided more effective control of pain in this setting and what was learned regarding the effects of the drugs on sleep.

A very interesting and challenging paper from Zonguldak and Ankara, Turkey (28) is featured in the Research Ideas section. The authors' offer insight into the management of the MPDS, sometimes referred to as the temporomandibular joint dysfunction syndrome. They evaluated the relative benefits of four medications commonly used in the management of this painful condition. Patients who entered the clinical trial were randomized into four active treatment groups. A fifth group served as a no-treatment control. The authors expressed surprise regarding the findings of their study so their question is naturally, where should we go from here? What recommendation should we make to the readers of our research study? The reader is encouraged to examine this paper and decide how a clinician should relate to the findings.

Please note the special interest columns which provide reviews of papers published in other medical journals since the previous issue of the JMP. The topics of these reviews are FMS, MPS, and other soft-tissue pain syndromes.

As always, readers of the JMP are invited to submit original manuscripts for blinded peer review, case reports of general interest, research ideas to promote further investigation, and letters to keep us all informed. The JMP editorial office frequently receives relevant books to be evaluated by and for the benefit of our readers. Book reviewers are allowed to keep the featured book after their evaluation report is completed. Readers who would be interested in being a book reviewer for the JMP, please communicate that to the editor [[email protected]]. Potential authors of contributions to the JMP should note that submissions and all communications between the authors and the JMP staff are to be accomplished online. Visit http://mc.manuscriptcentral.com/wjmp for more details.

The clear mandate of the International MYOPAIN Society [IMS], for which the JMP is the official journal, is to perpetuate the international meeting [MYOPAIN] that has been held every three years, but is moving soon to an every two-year schedule. The next International MYOPAIN Meeting will be MYOPAIN 2013, which will be held in the beautiful Pacific seacoast town of Seattle, Washington, United States. Two years later, the International MYOPAIN 2015 Meeting will be held on an elegant Pacific coast town of Sydney, Australia, as the IMS responds to the goal of better serving our growing numbers of members from Asia and the Pacific Rim. The IMS website www.myopain.com will offer details as they become available.

Be aware that Regional IMS Chapters are beginning to form. The first Regional IMS Chapter to be officially organized is in Thailand. Congratulations to them! The mastermind of that project was Pradit Prateepavanich, MD, PhD, whose contact information is Department of Rehabilitation Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand, EML: sippr@mahidol. ac.th, [email protected], in case others wish to learn how he did it.

The new IMS administrator is Larry E. Bodkin, Jr., M.S., CAE, Executive Director, IMS, 1876-B Eider Court, Tallahassee, Florida 32308, United States; Phone [phone] Fax [phone]; E-Mail [email protected]; Website www.myopain.org. He is responsible for the new look of the IMS website. Dues payment and new member applications can be tendered via the www.myopain.org website. All communications regarding IMS operations should be directed to Larry Bodkin and his staff. With Mr. Bodkin's experienced leadership, we can expect growth and progress on many fronts.