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The influence of deep (odontogenic) pain intensity, quality, and duration on the incidence and characteristics of referred orofacial pain.

This study examined the effects of the intensity, quality, and duration of odotogenic pain on the incidence, pattern, and clinical characteristics of pain referral in the orofacial region. Four hundred consecutive patients reporting with posterior toothache to the dental emergency clinic were included. Patients completed a standardized clinical questionnaire consisting of a numerical rating scale for pain intensity and chose verbal descriptors from a list of adjectives describing the quality of their pain. In addition, patients indicated sites to which pain referred by drawing on a mannequin* of the head and neck. Pain intensity was found to significantly affect the presence of referred pain (P < .005). However, neither duration nor quality of pain influenced the incidence of referred pain. Finally, pain referral occurred in vertical laminations as indicated on mannequin drawings, but these were not found to be diagnostic because of extensive horizontal overlap. The association of intensity and referral is attributed to central nervous system hyperexitability causing expansion of receptive fields and spread and referral of pain.

Adolescent↗

Pain epidemiology and health related quality of life in chronic non-malignant pain patients referred to a Danish multidisciplinary pain center.

This paper presents the results of a detailed study of the pain epidemiology and health related quality of life (HRQL) in 150 chronic non-malignant pain patients consecutively referred to a Danish multidisciplinary pain center. Mean pain severity was 71.6 (SD = 18.5) on the VAS scale. Forty-two percent reported poor quality of sleep. HRQL was evaluated with the Medical Outcome Study-Short Form (SF-36), the Hospital Anxiety and Depression scale (HAD) and the Psychological General Well-Being Scale (PGWB). Compared with the normal population (NP) both SF-36 scores and PGWB scores were significantly reduced (P < 0.001) indicating that physical, psychological and social well-being were severely reduced. On the HAD scale 58% were found to have a depressive or anxiety disorder. Statistically significant but modest correlations were found between pain severity and HRQL. Psychological and social well-being was closely correlated. Sixty-three percent of the referred patients had neurogenic pain conditions. Of these, only 25% were treated with antidepressants or anticonvulsants at referral. Seventy-three percent were treated with opioids at referral. Mean opioid consumption was 64 mg of morphine per day (range 1-280 mg). Compared with the NP the chronic pain patients had used the health care system five times more often in the years prior to referral (P < 0.001). The study confirms the severe multidimensional impact of chronic pain and demonstrates that HRQL of chronic non-malignant pain patients is among the lowest observed for any medical condition.

Adolescent↗

Similarity of distributions of spinal c-Fos and plasma extravasation after acute chemical irritation of the bladder and the prostate.

PURPOSE: Persistent pain in referred areas and voiding dysfunction are characteristic symptoms of chronic abacterial prostatitis. Since referred pain from visceral organs is considered a neurological event, it appeared reasonable to hypothesize that the persistent pain associated with prostatitis might also be explained by neural mechanisms. Neurogenic plasma extravasation and c-fos expression in the spinal cord, after chemical irritation of the rat prostate, was identified as a method to investigate the neurogenic aspect of prostatic inflammation. MATERIALS AND METHODS: The distribution of plasma extravasation using Evans blue dye was determined after chemical irritation of the prostate and bladder of the rat, and the distribution of dye extravasation was analyzed. c-fos expression within the spinal cord was determined immunocytochemically after chemical irritation of the prostate, bladder and superficial somatic region determined by the dye extravasation as a referred pain area (tail root). RESULTS: Chemical irritation of the prostate resulted in plasma extravasation in L5 to S2 dermatomes (primarily in L6 and S1). In rats receiving bladder irritation, the distribution of plasma extravasation showed a similar pattern to that observed in animals receiving prostatic irritation. Chemical irritation of the 3 structures resulted in expression of c-fos positive cells within the lumbosacral spinal cord. With each treatment the majority of c-fos positive cells were in the L6 and S1 segments. In all 3 groups the highest percentages of c-fos positive cells were observed in deeper laminae, including the dorsal commissure and sacral parasympathetic nucleus. CONCLUSIONS: Our results strongly suggest that referred pain status in inflammation of the bladder and prostate is neurogenically mediated. Based on these studies, there should be significant overlaps of nociceptive neurons within the spinal cord, which receive nociceptive inputs from pelvic soma and viscera.

Animals↗

Short latency cerebral response evoked by painful electrical stimulation applied to the human sigmoid colon and to the convergent referred somatic pain area.

Background. The brain-gut interaction is important for the understanding of pain mechanisms related to gastroenterological diseases. Unfortunately little is known about the early cerebral events related to the processing of gut-evoked pain. The aims of this human study were (1) to investigate the early-evoked brain potentials (EPs) to painful sigmoid colon stimulation and (2) to evaluate the EPs evoked from the convergent referred skin pain area after this area was induced by the painful gut stimulation. The background for the second aim was to evaluate whether the convergent input between somatic and visceral structures could induce detectable short-term cortical reorganization. Methods. Eleven subjects (nine men) participated; the mean age was 39.5+/-11.9 years. The gut-evoked EPs (recorded from 31 scalp sites) were evoked by electrical stimulation 30 cm from the anal verge by a modified biopsy forceps, inserted through a sigmoidoscope. The painful gut stimulation elicited a characteristic pain pattern referred to the abdomen. The short latency somatosensory evoked potentials were evoked from the skin inside and outside the referred pain area elicited by gut stimulation. A total of 750 electrical stimuli were delivered to the gut at slight painful stimulus intensity and 500 stimuli were delivered to the skin. Results. Short-latency EPs to electrical gut stimulation with an onset of 50-60 ms could be recorded. The gut EP topography revealed three consecutive positive peaks (P63, P101, P145) towards the frontal area. Centroparietal negativities (N128 and N222) were found, which were followed by two central positivities (P269 and P352). The somatic and gut evoked EPs differed in morphology and topography, but the EPs to skin stimulation inside and outside the gut-evoked referred pain area did not differ significantly. Conclusion. Short latency (50-60 ms) EPs to painful electrical sigmoid colon stimulation were demonstrated, reflecting an early cortical processing of sensory input from the sigmoid colon. The early cortical processing of somatic input from experimentally evoked visceral referred pain areas did not cause any detectable short-term cortical reorganization.

Adult↗

Stimulus-response functions in areas with experimentally induced referred muscle pain--a psychophysical study.

Few clinical or experimental studies have carried out systematic investigations of cutaneous and deep sensibility in areas with referred muscle pain. Therefore, no clear signs of increased or decreased psychophysical responses to various somatosensory stimuli are found in referred pain areas. In the present study, a total of 7.1 ml 5% hypertonic saline was infused over 900 s into the m. tibialis anterior of 11 subjects. This produced local muscle pain and pain referred to the ventral aspect of the ankle. A continuous recording of the ongoing pain intensities of the local and referred pain was carried out on two electronic visual analogue scales (VAS). Before, during and 30 min after the period with referred pain, radiant heat (argon laser) stimuli, single and repeated electrical stimuli, and pressure stimuli were applied to the referred pain area. Stimulus-response (SR) functions were obtained by means of pain intensity ratings of the different stimuli at 75%, 112.5% and 150% of the individual pain threshold (PT) intensity. The pain intensities of contact heat (thermode) stimuli at 40 degrees C, 47 degrees C and 50 degrees C and pin-prick stimuli with von Frey hair were also assessed in the referred pain area. The saline-induced local muscle pain intensity was higher than the intensity of the referred pain (P < 0.05). The referred pain intensity was significantly higher in the 20-460 s interval than in the 460-900 s interval (P < 0.05). This difference was not seen for the local muscle pain. During the period with referred pain, significantly decreased responses to radiant heat and pressure stimuli were found at 112.5% and 150% of PT intensity (P < 0.05). Further, significantly increased responses to single and repeated electrical stimuli at 75% and 112.5% of PT intensity (P < 0.05) were also found. After the period with referred pain, a considerably decreased response to single and repeated, electrical stimuli (P < 0.05) was present together with significantly increased responses to contact heat stimuli at 40 degrees C and radiant heat stimuli at 75% of PT intensity (P < 0.05). The present results suggest that ongoing muscle pain can cause modality-specific (and bi-directional) sensory changes in the referred pain area. This could explain why previous studies have reported both decreased and increased responses in referred pain areas.

Adult↗

Quantification of local and referred muscle pain in humans after sequential i.m. injections of hypertonic saline.

The aim of the present study was to test (1) whether muscle pain is influenced by temporal and spatial summation, and (2) whether sequential noxious muscle stimuli applied at hourly interstimulus-intervals could produce an increased sensation of pain due to central hyperexcitability. In the study eleven healthy men were exposed to computer-controlled intramuscular infusion of saline (5%) given over 20 s in m. tibialis anterior (m. TA). The intensities of local and referred pain were assessed by recordings on visual analogue scales (VAS), and the areas of local pain (around the injection site) and referred pain (outside the local pain area) were localised by the subject. Three experiments were performed. Experiment 1: Each subject participated in three tests separated by one week: (a) bolus (0.4 ml saline) infusion at one site; (b) four sequential infusions (0.1 ml saline) given at 90-s interstimulus-intervals at one site; and (c) four sequential infusions (0.1 ml saline) given at 360-s interstimulus-intervals at one site. Experiment 2: This was performed as experiment 1, but the infusions were given at spatially separated sites. Experiment 3. Hypertonic saline (0.1 ml) was injected one, four and 24 h after the sequential infusions (90-s interstimulus-intervals) given at spatially separated sites. The highest VAS peak and the largest local and referred pain areas were found after the bolus infusions. Compared to the first infusion, significant increases were found in the VAS peak, the size of the local pain area, and the size of the referred pain area (non-significant) after the four sequential infusions given at 90-s interstimulus-intervals (temporal summation). Four spatially separated infusions given simultaneously produced a higher VAS peak, a larger local pain area, and a larger referred pain area (non-significant) compared to one infusion (spatial summation). The infusion given 4 h after the sequential infusions tended to produce an increase in the referred pain area and in the pain intensity. In all three experiments significant correlations were found between the VAS peak and the size of the local (R = 0.64, P < 0.0001, n = 231) and referred (R = 0.47, P < 0.0001, n = 231) pain areas. Based on the above results it can be concluded that experimental muscle pain is influenced by temporal and spatial summation.

Adult↗

Acetazolamide reduces referred postoperative pain after laparoscopic surgery with carbon dioxide insufflation.

BACKGROUND: Carbon dioxide is the preferred insufflating gas for laparoscopy because of greater safety in the event of intravenous embolism, but it causes abdominal and referred pain. Acidification of the peritoneum by carbonic acid may be the major cause of pain from carbon dioxide insufflation. Carbonic anhydrase is an enzyme that increases the rate of carbonic acid formation from carbon dioxide. Because acetazolamide inhibits carbonic anhydrase, the authors hypothesized that the pain caused by carbon dioxide insufflation may be decreased by the administration of acetazolamide. METHODS: A prospective, randomized, double-blind study of 38 patients undergoing laparoscopic surgery during general anesthesia was performed. Acetazolamide (5 mg/kg) or a saline placebo was administered intravenously during surgery. Pain was rated on a visual analog scale (0-10) at four times: when first awake, at discharge from the recovery room, when discharged from the hospital, and on the day after surgery. The site and quality of pain were recorded, as were medications and side effects. RESULTS: Initial referred pain scores were lower after acetazolamide (1.00 +/- 1.98; n = 18) than after placebo (3.40 +/- 3.48; n = 20; P = 0.014), and 78% of patients in the acetazolamide group had no referred pain; however, only 45% patients in the placebo group had no referred pain. Incisional pain scores were not statistically different, and referred pain scores were similar at later times. CONCLUSIONS: Acetazolamide reduces referred but not incisional pain after laparoscopic surgical procedures. The duration of pain reduction is limited to the immediate postsurgical period.

Acetazolamide↗

Referred limb symptoms in chronic low back pain.

Referred limb symptoms (RLS) in chronic low back pain patients without signs of root affections were studied in 212 men and 126 women, aged 36-55 years, who were at work, but suffered from chronic or recurrent low back pain. RLS during the past few months were experienced by 17% daily and 22% occasionally. Previous RLS were reported by 34%, whereas 27% had never had such symptoms. There was a 3:4 distribution between symptoms in right and left legs, and 30% claimed symptoms in both legs. The distal extension of RLS into the limbs was as follows: thigh 18%, leg 37%, foot 20%, and toes 26%. The nature of RLS comprised the following: pain 56%, numbness 50%, cramps 22%, sharp pain 15%, and weakness 10%. Occurrence of RLS was not related to age. In both men and women, RLS correlated with subjective disability as well as with pain on bendings and palpation of lumbar spine and muscles. Men with previous and present RLS had greater external rotation of the hips, but otherwise no specific physical measurements were related with RLS. RLS of both legs in women and of distal extension in men showed more findings related with back pain.

Adult↗

Reference of pain following percutaneous cervical cordotomy.

In order to clarify the mechanism of reference of pain following cordotomy (ROPC), the authors investigated ROPC in 66 patients undergoing percutaneous cervical cordotomy (PCC) and examined the features of ROPC and the correlation between the occurrence of ROPC and the pre-operative pain states, as well as the results of PCC. ROPC was observed in 7 patients. It occurred immediately after PCC in 6 of 7 patients and 6 h after PCC in 1 patient. The pain was referred horizontally and cranially from the region rendered totally or largely analgesic by PCC to the normally innervated region. The region to which the pain was referred was not fixed. The referred pain disappeared by rendering the region where referred pain was felt analgesic with additional PCC. There was no correlation between the occurrence of ROPC and pre-operative pain states, or the results of PCC. From these results we postulate that: (1) ROPC occurs via a subsidiary pathway consisting of ascending chains of short neurons connecting dorsal horn neurons longitudinally and latitudinally; (2) the subsidiary pathway is inhibited under normal conditions by feedback inhibition from second-order neurons and/or higher central neurons of the nociceptive pathway; and (3) ROPC results from the release of the feedback inhibition by cordotomy.

Adolescent↗

The lumbar multifidus muscle and patterns of pain.

This paper describes the patterns of pain induced by injecting hypertonic saline into the lumbar multifidus muscle opposite the L5 spinous process in 15 healthy adult volunteers. All subjects experienced local pain while referred pain was reported by 13 subjects in one of two regions of the thigh; anterior (n=5) or posterior (n=8). These results confirm that the multifidus muscle may be a source of local and referred pain. Comparison of these maps with pain maps following stimulation of the L4 medial dorsal rami and L4-5 interspinous ligaments shows that pain arising from the band of multifidus innervated by the L4 dorsal ramus has a segmental distribution. In addition patterns of pain arising from multifidus clearly overlap those reported for other lumbar structures. These findings highlight the difficulty of using pain distribution to accurately identify specific lumbar structures as the source of pain.

Adult↗

Observations on muscle pain in man, with particular reference to pain during needle electromyography.

Muscle pain receptors have been studied in man. During the advance of an EMG needle pain is most regularly experienced as the muscle fascia is pierced. Further advancing the needle is usually quite painless. However, there are scantily distributed points within the muscle (`pain spots') which may give rise to pain if encountered by the advancing needle. The nature of the responsible receptors is obscure but it is likely that pain may sometimes be caused by activation of nerve fibres (presumably from these receptors) coursing through the muscle rather than by activation of the receptors themselves. Intramuscular bleeding is unlikely to contribute often to the pain of needle electromyography. Mechanically sensitive `pain spots' are more painful than other areas when stimulated electrically or injected with hypertonic (6%) saline. This suggests a common receptor. The high electrical threshold and relative invulnerability to pressure of afferent fibres from these receptors suggest that they are mainly of small diameter. These findings are discussed in relation to experimental work on pressure-pain receptors in animals.

Electric Stimulation↗

Sympathetic facilitation of hyperalgesia evoked from myofascial tender and trigger points in patients with unilateral shoulder pain.

OBJECTIVE: To provide evidence for the sympathetic-sensory interaction within a trigger point, which may contribute to local and referred pain and sympathetic symptoms in myofascial pain syndrome. METHODS: Pressure pain threshold (PPT) was measured from a trigger point in the painful side, from a tender point in the non-painful side in the infraspinatus muscles, and from a normal control point in the tibialis anterior muscle in 21 patients with unilateral shoulder pain. In addition, pressure threshold for eliciting referred pain (referred pain threshold, PTRP) was determined, then the intensity was measured of local and referred pain evoked by a pressure equal to 1.5 times PRPT, applied at the trigger point, in 11 patients. All measurements were taken during normal respiration and elevated intrathoracic pressure (EITP). RESULTS: PPT was significantly lower at the trigger than tender points during normal respiration (P=0.001). PPT decreased significantly at both the tender and trigger points during EITP compared with normal respiration (P<0.001). Significant decreases in referred pain threshold and increases in local and referred pain intensities were seen during EITP than normal respiration (all, P<0.01). CONCLUSIONS: These results provide evidence of sympathetic facilitation of mechanical sensitization and the local and referred muscle pain. SIGNIFICANCE: Sympathetic hyperactivity needs to be considered during the clinical evaluation and management of myofascial pain syndrome.

Adult↗

Mechanisms of referred visceral pain: uterine inflammation in the adult virgin rat results in neurogenic plasma extravasation in the skin.

The purpose of this study was to investigate the mechanisms of referred pain observed in female patients with pain from the reproductive organs. We developed a model of inflammatory uterine pain in the rat. Inflammation of the uterus in rats pretreated with Evans Blue Dye resulted in dye extravasation in the skin over the abdomen, groin, lower back, thighs, perineal area and proximal tail, thus providing for the first time evidence for the trophic changes observed in the area of referred visceral pain in an animal model of uterine pain. The neuronal pathways mediating the observed dye extravasation in the skin after uterine inflammation may include dichotomizing afferent fibers, afferent-afferent interactions via a spinal cord pathway or a sympathetic reflex. This model will allow to gain further insight into the mechanisms of referred pain and the trophic changes observed in the area of referred pain in visceral disease.

Animals↗

Cold and heat pain assessment of the human oesophagus after experimental sensitisation with acid.

The aim of the present study was to investigate the effect of thermal stimulation of the oesophagus before and after sensitisation with acid. In 17 healthy subjects a stimulation bag was used to re-circulate water at 5 and 60 degrees C for up to 90 s in the lower part of the oesophagus. The area under the temperature curve was used to assess the caloric load. The thermal stimuli were repeated after perfusion of the oesophagus with acid. The evoked pain intensity and referred pain areas (at the pain threshold) were assessed. At baseline the subjects were able to tolerate less caloric load (42%) for the heat compared to the cold stimuli (P = 0.007). The heat stimuli resulted in an increased referred pain area as compared with the cold stimuli (P = 0.03). Following acid perfusion there was a selective sensitisation to the heat pain stimuli as only 36% of the initial caloric load was tolerated (P = 0.012) whereas the sensation to the cold stimuli was unchanged. After acid perfusion, the referred pain area to the heat pain stimulation increased 49% (P = 0.04) but was not changed to cold stimulation (P = 0.82). After sensitisation the words used to describe the sensations to heat pain stimuli shifted from a warmth quality towards a more burning quality in most subjects. This multi-modal sensory testing study showed that acid sensitises the oesophagus to heat but not to cold pain. This may account for the modality-specific symptoms and hypersensitivity reported in patients suffering from, e.g. gastro-oesophageal reflux disease.

Acids↗

Shadows of the truth in patients with spinal pain: a review.

OBJECTIVE: Spinal pain with or without referred pain is a major and costly health problem that can arise from many anatomical structures. Sophisticated diagnostic imaging devices cannot show some of these structures, and frequently imaging provides only a shadow of the truth. This review illustrates how symptoms may well have an organic cause that is not detectable by current methods of examination, including imaging. METHOD: This study reviews some histopathological findings that can be associated with spinal pain with or without referred pain but cannot be seen on imaging. RESULT: Some histopathological changes illustrate imaging device limitations. CONCLUSION: Awareness of the considerable limitations of even sophisticated imaging devices is necessary when managing patients with acute or chronic spinal pain with or without referred pain. Symptoms may well be genuine and not of psychogenic origin: a diagnosis of malingering, therefore, should not be made lightly.

Adult↗

Focal headache during balloon inflation in the internal carotid and middle cerebral arteries.

Although a number of reports are available on the occurrence of headache in patients with ischemic cerebrovascular disease, most studies have recorded the frequency but not the specific sites of the pain. We report 18 patients who underwent balloon inflation in the distal internal carotid artery and middle cerebral artery stem during embolization therapy for intracerebral arteriovenous malformations. Eleven patients had reproducible patterns of headache during balloon inflation. Inflation in the proximal middle cerebral artery stem produced pain primarily in the ipsilateral temple, that in the middle of the middle cerebral artery stem produced pain referred primarily retro-orbitally, and inflation in the distal middle cerebral artery stem produced pain referred primarily to the forehead. Experimental studies have demonstrated similar patterns of referred pain. The fact that these areas of referred pain are so reproducible is of potentially great clinical importance in the approach to management of patients with cerebrovascular disease.

Adult↗