Chronic whiplash and central sensitization; an evaluation of the role of a myofascial trigger points in pain modulation

Christopher Centeno,Ake Nystrom,Michael Freeman

doi:10.1186/1749-7221-4-2

Abstract

Objectiveit has been established that chronic neck pain following whiplash is associated with the phenomenon of central sensitization, in which injured and uninjured parts of the body exhibit lowered pain thresholds due to an alteration in central pain processing. it has furthermore been hypothesized that peripheral sources of nociception in the muscles may perpetuate central sensitization in chronic whiplash. the hypothesis explored in the present study was whether myofascial trigger points serve as a modulator of central sensitization in subjects with chronic neck pain.Designcontrolled case series.Settingoutpatient chronic pain clinic.Subjectsseventeen patients with chronic and intractable neck pain and 10 healthy controls without complaints of neck pain.Interventionsymptomatic subjects received anesthetic infiltration of myofascial trigger points in the upper trapezius muscles and controls received the anesthetic in the thigh.Outcome measures: pre and post injection cervical range of motion, pressure pain thresholds (ppt) over the infraspinatus, wrist extensor, and tibialis anterior muscles. sensitivity to light (photophobia) and subjects' perception of pain using a visual analog scale (vas) were also evaluated before and after injections. only the ppt was evaluated in the asymptomatic controls.Resultsimmediate (within 1 minute) alterations in cervical range of motion and pressure pain thresholds were observed following an average of 3.8 injections with 1–2 cc of 1% lidocaine into carefully identified trigger points. cervical range of motion increased by an average of 49% (p = 0.000) in flexion and 44% (p = 0.001) in extension, 47% (p = 0.000) and 28% (p < 0.016) in right and left lateral flexion, and a 27% (p = 0.002) and 45% (p = 0.000) in right and left rotation. ppt were found increased by 68% over the infraspinatus (p = 0.000), by 78% over the wrist extensors (p = 0.000), and by 64% over the tibialis anterior (p = 0.002). among 11 subjects with photophobia, only 2 remained sensitive to light after the trigger point injections (p = 0.033). average vas dropped by 57%, from 6.1 to 2.6 (p = 0.000). no significant changes in ppt were observed in the control group following lidocaine infiltration of the thigh.Conclusionthe present data suggest that myofascial trigger points serve to perpetuate lowered pain thresholds in uninjured tissues. additionally, it appears that lowered pain thresholds associated with central sensitization can be immediately reversed, even when associated with long standing chronic neck pain. although the effects resulting from anesthesia of trigger points in the present study were temporary, it is possible that surgical excision or ablation of the same trigger points may offer more permanent solutions for chronic neck pain patients. further study is needed to evaluate these and other options for such patients.

Highlights

[1] Several authors have described lowered pain thresholds in uninjured tissues, and explained the finding as the expression of an abnormal processing of nociceptive information in the brain and spinal cord. [2,3,4,5,6,7] Others have postulated that chronicposttraumatic myalgia mayperpetuateandaccentuate thepain status of afflicted patients, [8,9] and Ge et al recently reported experimental evidence of a physiologic link between myofascial trigger points and central sensitization in patients with shoulder pain of myofascial origin
[10] In contrast, Curatolo et al, in a study of chronic whiplash patients, reported that anesthetic infiltration of painful or tender points did not alter the signs of central sensitization
In the present study the authors set out to evaluate whether anesthetic infiltration of myofascial trigger points in patients with chronic and refractory neck pain can affect pain thresholds in uninjured parts of the body

Summary

Introduction

Chronic pain from injury, including injury from whiplash trauma, is associated with centrally mediated hyperalgesia, known as central sensitization. [1] Several authors have described lowered pain thresholds in uninjured tissues, and explained the finding as the expression of an abnormal processing of nociceptive information in the brain and spinal cord. [2,3,4,5,6,7] Others have postulated that chronicposttraumatic myalgia (muscle pains) mayperpetuateandaccentuate thepain status of afflicted patients, [8,9] and Ge et al recently reported experimental evidence of a physiologic link between myofascial trigger points and central sensitization in patients with shoulder pain of myofascial origin. [10] In contrast, Curatolo et al, in a study of chronic whiplash patients, reported that anesthetic infiltration of painful or tender points did not alter the signs of central sensitization. [11] An explanation for this discrepancy may lie in the definition of what constitutes a myofascial pain generator. [10] In contrast, Curatolo et al, in a study of chronic whiplash patients, reported that anesthetic infiltration of painful or tender points did not alter the signs of central sensitization. [11] An explanation for this discrepancy may lie in the definition of what constitutes a myofascial pain generator While both 'tender points' and myofascial trigger points are painful to palpation, only myofascial trigger points will fasciculate or "twitch" when probed with a needle. In the present study the authors set out to evaluate whether anesthetic infiltration of myofascial trigger points in patients with chronic and refractory neck pain can affect pain thresholds in uninjured parts of the body While both 'tender points' and myofascial trigger points are painful to palpation, only myofascial trigger points will fasciculate or "twitch" when probed with a needle. [12] The presence of a twitch response to needle probing has been experimentally demonstrated as a necessary prerequisite for trigger point deactivation and pain relief with local anesthetic injection. [13] Based on these previously reported findings, it is reasonable to hypothesize that anesthetization of carefully identified trigger points may alter findings of central sensitization in patients with chronic neck pain.

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