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Interexaminer reliability of the palpation of trigger points in the trunk and lower limb muscles.

OBJECTIVES: To determine the interexaminer reliability of palpation of three characteristics of trigger points (taut band, local twitch response, and referred pain) in patients with subacute low back pain, to determine whether training in palpation would improve reliability, and whether there was a difference between the physiatric and chiropractic physicians. DESIGN: Reliability study. SETTING: Whittier Health Campus, Los Angeles College of Chiropractic. PARTICIPANTS: Twenty-six nonsymptomatic individuals and 26 individuals with subacute low back pain. INTERVENTION: Twenty muscles per individual were first palpated by an expert and then randomly by four physician examiners. MAIN OUTCOME MEASURES: Palpation findings. RESULTS: Kappa scores for palpation of taut bands, local twitch responses, and referred pain were .215, .123, and .342, respectively, between the expert and the trained examiners, and .050, .118, and .326, respectively, between the expert and the untrained examiners. Kappa scores for agreement for palpation of taut bands, twitch responses, and referred pain were .108, -.001, and .435, respectively, among the nonexpert, trained examiners, and -.019, .022, and .320, respectively, among the nonexpert, untrained examiners. CONCLUSIONS: Among nonexpert physicians, physiatric or chiropractic, trigger point palpation is not reliable for detecting taut band and local twitch response, and only marginally reliable for referred pain after training.

Adult↗

Deficits in visceral pain and referred hyperalgesia in Nav1.8 (SNS/PN3)-null mice.

The tetrodotoxin-resistant sodium channel alpha subunit Nav1.8 is expressed exclusively in primary sensory neurons and is proposed to play an important role in sensitization of nociceptors. Here we compared visceral pain and referred hyperalgesia in Nav1.8-null mice and their wild-type littermates in five tests that differ in the degree to which behavior depends on spontaneous, ongoing firing in sensitized nociceptors. Nav1.8-null mice showed normal nociceptive behavior provoked by acute noxious stimulation of abdominal viscera (intracolonic saline or intraperitoneal acetylcholine). However, Nav1.8-null mutants showed weak pain and no referred hyperalgesia to intracolonic capsaicin, a model in which behavior is sustained by ongoing activity in nociceptors sensitized by the initial application. Nav1.8-null mice also showed blunted pain and hyperalgesia to intracolonic mustard oil, which sensitizes nociceptors but also provokes tissue damage. To distinguish between a possible role for Nav1.8 in ongoing activity per se and ongoing activity after sensitization in the absence of additional stimuli, we tried a visceral model of tonic noxious chemical stimulation, cyclophosphamide cystitis. Cyclophosphamide produces cystitis by gradual accumulation of toxic metabolites in the bladder. In this model, Nav1.8-null mice showed normal responses. There were no differences between null mutants and their normal littermates in tissue damage and inflammation evoked by any of the stimuli tested, suggesting that the behavioral differences are not secondary to impairment of inflammatory responses. We conclude that there is an essential role for Nav1.8 in mediating spontaneous activity in sensitized nociceptors.

Acetylcholine↗

Noninvasive discrimination of brachial plexus involvement in upper limb pain.

The ability of Elvey's "brachial plexus tension test" to identify pain referred from the cervical region was investigated in 50 patients with unilateral shoulder and upper arm pain: 25 reported symptoms commencing after open heart surgery, indicating a high probability of referred pain due to that procedure; 25 were athletes with injuries from throwing movements, a cause appearing much less likely to cause referred pain. Twenty-five asymptomatic subjects with no history of spinal or limb pain also were tested. Cervical and upper limb maneuvers of the test were assessed goniometrically. The cardiac group showed significantly greater test results than those of the other groups, suggesting that the test is able to discriminate referred and local sources of upper limb pain.

Adult↗

Atlanto-occipital and lateral atlanto-axial joint pain patterns.

STUDY DESIGN: Five asymptomatic subjects underwent provocative injections of the lateral atlanto-axial and atlanto-occipital joints. OBJECTIVES: This study isolated and stimulated the lateral atlanto-axial and atlanto-occipital joints via fluoroscopically guided intra-articular injections to determine if they are potential pain generators. If they are pain generators, preliminary pain pattern maps will be constructed. SUMMARY OF BACKGROUND DATA: The cervical zygapophyseal joints (C2-3 to C6-7) are potential pain generators as demonstrated by referred pain induced via isolated intra-articular joint injections in normal subjects. Tentative referral patterns based on direct mechanical stimulation of the lateral atlanto-axial and atlanto-occipital joints have not been reported. METHODS: Five volunteers without histories of upper cervical pain underwent two joint injections each. In all five subjects, the left atlanto-occipital and right lateral atlanto-axial joints were stimulated via injection of contrast medium causing distension of the joint capsule. RESULTS: Referred pain was produced with all ten injections. The lateral atlanto-axial injections resulted in consistent referral patterns, whereas the atlanto-occipital referral patterns varied significantly. A tentative composite diagram of the experimentally induced pain was created for each joint. CONCLUSION: This study confirms the nociceptive ability of these cervical synovial joints. This study may assist the clinician in the differential diagnosis of head and neck pain.

Adult↗

Peripheral and central mechanisms of cutaneous hyperalgesia.

Hyperalgesia after cutaneous injury can be divided into two phenomena: Primary hyperalgesia occurs at the site of injury and is characterized by hyperalgesia to mechanical and heat stimuli. Secondary hyperalgesia occurs outside the injury site and is characterized by mechanical hyperalgesia only. Hyperalgesia in inflammatory processes corresponds to primary hyperalgesia. Hyperalgesia in referred pain and neuropathic pain resembles secondary hyperalgesia (Table 3). Evidence for the latter would be strengthened if hyperalgesia to cooling stimuli, which is observed in neuropathic pain, was also demonstrated in referred pain and in secondary hyperalgesia. Some of the more likely neural mechanisms to explain primary and secondary hyperalgesia are illustrated in Fig. 8. Primary hyperalgesia to heat stimuli has a counterpart in the sensitization of peripheral nociceptors to heat stimuli (Fig. 8A), leading to similar changes in central neurons. In addition, the enlargement of the mechanical receptive field of primary afferent nociceptors to include the site of injury may account for the primary hyperalgesia to mechanical stimuli (Fig. 8B). In the literature, there are some contradictions with respect to the stimulus modalities to which hyperalgesia and sensitization occur. In spite of the well-documented sensitization of primary afferent nociceptors to heat stimuli, there are few studies on its molecular mechanisms. On the other hand, there is pharmacological evidence for a peripheral mechanism of primary mechanical hyperalgesia, but little direct evidence that nociceptors can be sensitized to mechanical stimuli by injury. This contradiction should spawn further investigations into the mechanical response properties of nociceptors and into the molecular mechanisms of heat sensitization. Secondary hyperalgesia to mechanical stimuli is likely due to the sensitization of central pain signalling neurons (CPSNs). This sensitization could involve only input from nociceptors (Fig. 8C), since mechanical pain thresholds after a cutaneous injury are of the same order as those of nociceptors. Central sensitization could also be the result of enhanced connectivity between low-threshold mechanoreceptors and CPSNs (Fig. 8D). This form of sensitization may account for the pain to light touch associated with neuropathic pain. Receptive field plasticity is a prevalent property of dorsal horn neurons and probably plays a vital role with regard to hyperalgesia. The molecular mechanisms of synaptic plasticity are currently subject to intense experimental investigation and may provide new insights on the mechanisms of pain and hyperalgesia.

Animals↗

Qualitative review of studies of manipulation-induced hypoalgesia.

BACKGROUND: The number of studies that have investigated the direct analgesic effect of a spinal manipulation on spinal or referred pain is small, making knowledge of this crucial aspect of manipulation sparse. This paper reviews a set of studies that measure the immediate effect of manipulation on pain or pain-related phenomena in the spinal and peripheral soft tissues. METHODS: The literature was accessed through MEDLINE. Key words used were "manipulation," "pain," and "chiropractic." This search was complemented by citation reviews of important research and chapters on the topic. Only studies that directly measured the effect of at least a single spinal manipulation on pain (eg, tenderness, biochemical assay, referred pain) were selected. The selected studies were reviewed descriptively; no systematic assessment of their quality was conducted. RESULTS: The electronic search yielded 738 citations. Six hundred and forty-two were relevant to chiropractic. Of these, most were clinically descriptive articles about diagnostic and therapeutic procedures or case management. Most of the remaining articles were clinical trial reports or letters to the editor. Only 5 studies were selected according to the established criteria. Thus less than 1% of the indexed literature on chiropractic, manipulation, and pain involved studies that explored the mechanism of the putative effect of spinal manipulation on pain mechanisms. Six other studies were retrieved from citation reviews. These 11 studies were reviewed in order publication. CONCLUSION: Few studies have investigated the effects of spinal manipulation on pain directly. If the theory of manipulation exerting its therapeutic effects posits that the sensory input created by the intervention results in some form of inhibition of pain, then the results of these studies are largely consistent with one another and with this theory. This review has highlighted the deficiencies in the extant studies and many remaining questions. Only more high-quality research will permit a full elucidation of the hypoalgesic effects of spinal manipulation.

Analgesia↗

Trigger points in the suboccipital muscles and forward head posture in tension-type headache.

OBJECTIVE: To assess the presence of trigger points (TrPs) in the suboccipital muscles and forward head posture (FHP) in subjects with chronic tension-type headache (CTTH) and in healthy subjects, and to evaluate the relationship of TrPs and FHP with headache intensity, duration, and frequency. BACKGROUND: Tension-type headache (TTH) is a prototypical headache in which myofascial TrPs in the cervical and pericranial musculature can play an important role. DESIGN: A blinded, controlled pilot study. METHODS: Twenty CTTH subjects and 20 matched controls without headache participated. TrPs were identified by eliciting referred pain with palpation, and increased referred pain with muscle contraction. Side-view pictures of each subject were taken in sitting and standing positions, in order to assess FHP by measuring the craniovertebral angle. Both measures were taken by a blinded assessor. A headache diary was kept for 4 weeks in order to assess headache intensity, frequency, and duration. RESULTS: Sixty-five percent (13/20) CTTH subjects showed active TrPs and 35% (7/20) had latent TrPs in the suboccipital muscles. Six (30%) controls also had latent TrPs. Differences in the presence of suboccipital muscle TrPs between both the groups were significant for active TrPs (P < .001) but not for latent TrPs (P > .5). CTTH subjects with active TrPs reported a greater headache intensity and frequency than those with latent TrPs (P < .05). The degree of FHP was greater in CTTH subjects than in controls in both sitting and standing positions (P < .01). Within the CTTH group, there was a negative correlation between the craniovertebral angle and the frequency of headache (r(s) = -0.6, P < .01, in sitting position; r(s) = -0.5, P < .05, in standing position). CTTH subjects with active TrPs had a greater FHP than those with latent TrPs, though this difference was not significant. CONCLUSIONS: Suboccipital active TrPs and FHP were associated with CTTH. CCTH subjects with active TrPs reported a greater headache intensity and frequency than those with latent TrPs. The degree of FHP correlated positively with headache duration, headache frequency, and the presence of suboccipital active TrPs.

Adult↗

Neural connection between the ventral portion of the lumbar intervertebral disc and the groin skin.

This study was designed to investigate neural mechanisms of referred pain in lumbar intervertebral disc lesions. Patients with a degenerative disc in lower lumbar segments occasionally complain of groin pain, which cannot be explained anatomically as having a radicular origin. In rats pretreated with intravenous application of Evans blue dye, the dye extravasation appeared in the groin skin after application of capsaicin to the ventral portion of the L5-6 intervertebral disc. This response occurred even in rats with a sectioned L-5 spinal nerve and sympathetic trunks, but did not occur in rats with a sectioned genitofemoral nerve. Capsaicin topically applied to the sciatic nerve did not cause dye extravasation in the hindpaw. Therefore, groin dye extravasation was not due to a direct effect of capsaicin but, rather, presumably was caused by an "antidromic axon reflex" of dichotomizing C fibers or to a segmental sympathetic reflex causing vascular permeability. The present results indicate that the ventral portion of the lumbar discs is neurally connected to the groin skin via the upper (L-2) lumbar spinal nerves in rats. Groin pain coincident with low-back pain may be explained as referred pain, indicating that a lesion is present in the ventral portion of the lumbar intervertebral disc space.

Animals↗

Cerebral response to electric stimulation of the colon and abdominal skin in healthy subjects and patients with irritable bowel syndrome.

BACKGROUND: Visceral hyperalgesia may play an important part in the pathophysiology of the irritable bowel syndrome (IBS). We investigated the neuronal afferent pathways in healthy volunteers and IBS patients by recording evoked potentials (EPs) elicited by electrical stimulation of the colon and abdominal skin inside and outside the referred pain area. METHODS: Six healthy subjects and nine IBS patients met the inclusion criteria. Morphology and topography of EPs to painful electrical stimuli were estimated in the rectosigmoid junction and on the skin inside/outside the referred pain areas. RESULTS: The EPs to painful stimuli of the gut showed a shorter latency and a smaller amplitude of the first positive peak (P1) in the IBS group. The controls had a mid-latency frontal positive component after 100 ms, whereas no reliable early activation was seen in the IBS patients. In controls, a single late (>150 ms) positive component was seen, whereas the late component was biphasic in the IBS group. The EPs to painful stimuli of the two skin areas differed in IBS patients, but not in controls. CONCLUSION: Differences in the EPs to electrical painful stimulation of the sigmoid colon and skin inside/outside the experimentally evoked referred pain area were seen comparing healthy subjects and IBS patients. The results indicate altered central nervous system responses.

Abdomen↗

Urologic myofascial pain syndromes.

Treatment of pain of urogenital origin, chronic pelvic pain syndrome, can be frustrating for patients and physicians. The usual approaches do not always produce the desired results. Visceral pain from pelvic organs and myofascial pain from muscle trigger points share common characteristics. Referred pain from myofascial trigger points can mimic visceral pain syndromes and visceral pain syndromes can induce trigger point development and myofascial pain and dysfunction. The referred pain syndrome can long outlast the initial event, making diagnosis difficult.

Cystitis↗

Recognizing specific characteristics of nonspecific low back pain.

A retrospective review of 1293 cases of low back pain treated over a 12-year period revealed that sacroiliac joint syndrome and posterior joint syndromes were the most common referred-pain syndromes, whereas herniated nucleus pulposus and lateral spinal stenosis were the most common nerve root compression lesions. Referred pain syndromes occur nearly twice as often and frequently mimic the clinical presentation of nerve root compression syndromes. Combined lesions occurred in 33.5% of cases. Lateral spinal stenosis and herniated nucleus pulposus coexisted in 17.7%. In 30% of the cases of spondylolisthesis, the radiographic findings were incidental and the source of pain was the sacroiliac joint. Distinguishing radicular from referred pain, recognition of coexisting lesions, and correlation of diagnostic imaging with the overall clinical presentation facilities formulation of a rational plan of therapy. The above-outlined approach to managing low back pain evolved over a 12-year period. Designed to establish a specific diagnosis, it should yield excellent or good results in 84% of patients.

Back Pain↗

Antenatal women with or without pelvic pain can be characterized by generalized or segmental hypoalgesia in late pregnancy.

The aims of the present study were to determine the influence of pregnancy on somatosensory responses in women with or without pelvic/lumbosacral pain. Thirty pregnant women participated and were divided into pain (n = 12) and nonpain (n = 18) groups on the basis of pain complaints and positive pain-provoking tests associated with pelvic or lumbosacral pain during the current pregnancy. In the pain group, 9 reported initial pain in trimester 1, 2 in trimester 2, and 1 in trimester 3. Quantitative sensory testing with pressure pain threshold (PPT), heat pain threshold (HPT), and tactile threshold (TT) was performed once during each of the 3 trimesters at referred pain sites (sacrum, back, and pubis) and no pain control sites (thigh, arm, and sternum). All subjects in the pain group reported back pain, and 91% also had pain at the sacrum and pubis. The pain group exhibited significantly greater pain sensitivity than the nonpain group. The HPT and PPT were higher in trimester 3 as compared to trimesters 1 and 2 (P < .012). The increase in thresholds, or hypoalgesia, was generalized and present at both referred pain and control sites in the pain group. In the nonpain group hypoalgesia was localized to the presumed referred pain sites at the back and sacrum. There were no significant variations in the TT in any trimester. The study demonstrates for the first time that hypoalgesia in late pregnancy is generalized in women with pelvic pain and localized in women without pelvic pain. This suggests that the descending noxious inhibitory system is activated in late pregnancy and is probably more intense and generally activated in women with pelvic pain and only segmentally activated in women without pain.

Journal Article↗

[Assessment of muscle pain and hyperalgesia. Experimental and clinical findings].

AIM: It is evident that muscle hyperalgesia and referred pain have an important role in chronic musculoskeletal pain. More knowledge of the basic mechanisms involved and better methods of assessing muscle pain in clinical practice are needed so that treatment regimens can be revised and improved. METHODS: Methods of quantitative sensory testing of muscle pain and associated phenomena are described. These methods make it possible to evaluate manifestations of muscle pain in a standardised way both in patients suffering from musculoskeletal pain and in healthy volunteers. RESULTS: Elevated muscle sensitivity becomes manifest as (1) pain evoked by a normally non-noxious stimulus (allodynia), (2) abnormally intense pain evoked by noxious stimuli (hyperalgesia), or (3) unusually large areas of referred pain with associated somatosensory changes. These changes can occur as increased somatosensory sensitivity of deep somatic tissues or of the skin in areas of pain referral. Some manifestations of sensitisation in chronic musculoskeletal pain patients, such as expansion of the areas of referred muscle pain, can be explained by the extra segmental spread of central sensitisation seen in animal experiments. CONCLUSIONS: An important part of the manifestations of pain in chronic musculoskeletal disorders may be due to peripheral and central sensitisation processes, which are also involved in the transition from acute to chronic pain. Knowledge of these processes has expanded enormously in recent years; it should be utilised when new intervention strategies are designed.

Humans↗

Gender differences in pain modulation evoked by repeated injections of glutamate into the human trapezius muscle.

Gender differences in pain habituation, temporal summation, and pressure hyperalgesia evoked by repeated injections of glutamate into the dominant trapezius muscle were investigated. The glutamate-evoked muscle pain intensity and pressure pain threshold (PPT) were assessed. The PPTs were measured bilaterally in the trapezius muscles (local pain area) and posterolateral neck muscles (referred pain area) after glutamate injection in healthy and age-matched males and females (each n=14). Two glutamate injections (0.4 ml, 2M each) were injected with an interval of 5 min. One injection of glutamate (0.4 ml, 2M) served as a control. Males, but not females, rated the second injection (maximal pain intensity) significantly less painful than the first injection. The area under the visual analogue scale pain curve of the second injection was significantly larger than the first injection in females. Repeated glutamate injections, but not one-glutamate injection, significantly decreased PPTs in the local pain area, with no significant gender differences. No PPTs changes were observed either in the contralateral trapezius muscle or bilaterally in the referred pain areas in either sex. These results suggest that a less efficient pain habituation and a greater susceptibility to the development of temporal summation of muscle pain in females, but not in males, might be one of the contributing factors to the higher incidence of neck shoulder pain in females. In addition, the reduction of PPTs in the local pain area evoked by intramuscular glutamate injection may represent an early process of peripheral pressure hyperalgesia, which is most likely gender independent.

Adult↗

Local anesthetic effects in the presence of chronic osteomyelitis (necrosis) of the mandible: implications for localizing the etiologic sites of referred trigeminal pain.

The aims of this study were: (1) to demonstrate how reproducible variations in incomplete anesthesia of the inferior alveolar nerve can be used as a guide to locate the etiologic sites of referred trigeminal pain emanating from the mandible; (2) to describe the salient histopathologic features of a lowgrade, nonsuppurative osteomyelitis seen in this patient population. Forty-six patients with idiopathic facial pain were subjected to a specific protocol of local anesthetic injections to sequentially block branches of the mandibular nerve to determine the effects on his/her pain. If this significantly reduced or altered the pain on three separate appointments, then exploratory surgery was conducted near identified zones of unanesthetized gingiva. Blocking (92%), bridging (4%), and divergence (4%) were observed patterns of anesthetic resistance of the mucogingival tissues used to categorize the incomplete anesthesia. A 100% correlation was found between the identified zones of unanesthetized gingiva and the discovery of intramedullary pathology. Medullary fibrosis with ischemic and degenerative changes in the cancellous bone were common findings, along with chronic inflammatory cell infiltrates and clusters of lymphocytes. It is concluded that Ratner's method of diagnostic anesthesia be implemented when searching for occult pain producing pathology of the jaws.

Adult↗