Quantitative sensory testing before and after regional guanethidine block in patients with neuralgia in the hand

The Potential Role of Sensory Testing, Skin Biopsy, and Functional Brain Imaging as Biomarkers in Chronic Pain Clinical Trials: IMMPACT Considerations

Valid and reliable biomarkers can play an important role in clinical trials as indicators of biological or pathogenic processes or as a signal of treatment response. Currently, there are no biomarkers for pain qualified by the U.S. Food and Drug Administration or the European Medicines Agency for use in clinical trials. This article summarizes an Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials meeting in which 3 potential biomarkers were discussed for use in the development of analgesic treatments: 1) sensory testing, 2) skin punch biopsy, and 3) brain imaging. The empirical evidence supporting the use of these tests is described within the context of the 4 categories of biomarkers: 1) diagnostic, 2) prognostic, 3) predictive, and 4) pharmacodynamic. Although sensory testing, skin punch biopsy, and brain imaging are promising tools for pain in clinical trials, additional evidence is needed to further support and standardize these tests for use as biomarkers in pain clinical trials.

PERSPECTIVE

The applicability of sensory testing, skin biopsy, and brain imaging as diagnostic, prognostic, predictive, and pharmacodynamic biomarkers for use in analgesic treatment trials is considered. Evidence in support of their use and outlining problems is presented, as well as a call for further standardization and demonstrations of validity and reliability.

Comparison of operant escape and reflex tests of nociceptive sensitivity

Testing of reflexes such as flexion/withdrawal or licking/guarding is well established as the standard for evaluating nociceptive sensitivity and its modulation in preclinical investigations of laboratory animals. Concerns about this approach have been dismissed for practical reasons - reflex testing requires no training of the animals; it is simple to instrument; and responses are characterized by observers as latencies or thresholds for evocation. In order to evaluate this method, the present review summarizes a series of experiments in which reflex and operant escape responding are compared in normal animals and following surgical models of neuropathic pain or pharmacological intervention for pain. Particular attention is paid to relationships between reflex and escape responding and information on the pain sensitivity of normal human subjects or patients with pain. Numerous disparities between results for reflex and operant escape measures are described, but the results of operant testing are consistent with evidence from humans. Objective reasons are given for experimenters to choose between these and other methods of evaluating the nociceptive sensitivity of laboratory animals.

Cutaneous norepinephrine application in complex regional pain syndrome

Patients with complex regional pain syndrome (CRPS) (n=20) were examined in order to evaluate cutaneous reactions to norepinephrine (NE) on both the affected and the unaffected limb in comparison to healthy controls. Sixteen female and four male patients suffering from very acute and therefore untreated CRPS with a mean duration of 5.5 weeks were included in this study. Two groups of healthy volunteers served as control groups: the first group (n=18) according to the same study protocol as CRPS patients, and the second group (n=10) after warming up one limb. Norepinephrine was iontophoresized (0.2 mA, 120 s) and vasoconstriction was recorded by laser-doppler flowmetry. Pain sensations were simultaneously rated on a visual analogue scale (VAS). Five patients underwent a second trial with higher intracutaneous NE concentrations in order to study possible dose-dependent effects of NE on pain sensation. After acclimatization, skin temperature was recorded by infra-red thermography. The NE-induced reduction of skin blood flow was significantly higher in the affected limb in the patient group (33.0 vs 11.2%, p<0.005). None of the patients reported pain or hyperalgesia. The skin temperature of CRPS patients was significantly higher in the affected limb (34.7 vs 32.5 degrees C, p<0.001). The first control group did not show any difference between left and right sides concerning NE-induced vasoconstriction or skin temperature. The second control group had an increased unilateral skin temperature after warming up (35.0 vs 34.3 degrees C, p<0.006) and demonstrated a significantly increased vasoconstriction on the warmer side (52.0 vs 20.2%, p<0.03) corresponding to findings in patients with acute CRPS. The present study proves that there are signs of decreased sympathetic activity in the affected limb in very acute CRPS. However, no indication was found for increased sensitivity of vascular alpha-receptors in the very acute stages of CRPS, and there was also no indication for a significant direct contribution of the sympathetic nervous system to pain in very acute CRPS.

Modulation of sensitized C-fibers by adrenergic stimulation in human neuropathic pain

The chronic constriction injury model is widely used in studying mechanisms of neuropathic pain. In this model neuropathic pain can be influenced by sympathetic interventions. It is assumed that similar mechanisms as in animals are responsible for pain arising from nerve entrapment syndromes in humans. The aim of the present study was to investigate if in patients with nerve entrapment nociceptive afferents can be modulated by adrenergic stimulation.

METHODS

Twenty patients with pain due to a unilateral entrapment of the median nerve and 10 controls were included in the study. Spontaneous pain, mechanical and thermal evoked pain were assessed within the innervation territory of the lesioned nerve and the corresponding contralateral segment in patients and on the right hand side in healthy volunteers. The examinations were performed at baseline, during whole body cooling (sympathetic activation) and whole body warming (sympathetic inhibition), and after norepinephrine iontophoresis.

RESULTS

All patients reported spontaneous pain. Mechanical allodynia, punctate hyperalgesia and cold allodynia was not found. According to side-to-side differences in heat pain thresholds, patients were separated in patients with (n=10) and without (n=10) heat hyperalgesia. Adrenergic stimulation did not induce or enhance spontaneous or mechanical evoked pain in any patient or control subject. However in patients with pre-existing heat hyperalgesia sympathetic stimulation aggravated heat hyperalgesia significantly. Further in these patients the decrease in heat pain thresholds observed after norepinephrine iontophoresis was significantly higher compared to patients without pre-existing heat hyperalgesia.

CONCLUSION

Sympathetic-afferent interaction does not play a major role in pain generation due to nerve entrapment. Nevertheless in a subgroup of patients nociceptive afferents show sensitivity to physiological and pharmacological sympathetic stimulation. This finding is important because it emphasises that despite there is no clinical detectable effect on pain sympathetic afferent interaction can be found.

Cutaneous sensory abnormalities in children and adolescents with complex regional pain syndromes

Complex regional pain syndromes (CRPS) have been recognized with increasing frequency in children. These disorders appear to differ markedly from those observed in adults. The International Association for the Study of Pain diagnostic criteria for CRPS were developed based on adult studies; these criteria have not been validated for children. We performed standardized neurological examination and quantitative sensory testing (QST) in a group of pediatric patients to characterize features of sensory dysfunction. Forty-two patients, with unilateral lower extremity CRPS of a mean duration of the pain and symptoms of 12.6 months, who met IASP adult-based criteria for CRPS underwent standardized neurological examination and QST. QST parameters were compared to values previously derived from age- and sex-matched pediatric healthy controls. In most respects, QST parameters did not differ significantly between patients and the normal reference values except for cold and heat pain detection thresholds. Allodynia to cold and/or heat (P<0.001) occurred in 21 patients. Cold allodynia was the most common QST abnormality in our patients. Twenty-six patients showed a combination of mechanical dynamic and static allodynia and allodynia to punctate temporal summation. There was a significant correlation between mechanical dynamic allodynia and allodynia to punctate temporal summation (P<0.001). As with adult CRPS, the thermal and mechanical sensory abnormalities appear in different combinations in different patients with similar clinical presentations. In a majority of patients, the pathogenesis of pain is seemingly of central origin.

Effects of baclofen on temperature perception in humans

The aim of this study was to evaluate the effect of chronic consumption of the GABAB agonist baclofen on temperature perception in humans. We investigated temperature perception thresholds to detect warm and cold stimuli in a group of 21 patients with spinal cord injury, who were chronically consuming oral baclofen at different daily doses to treat spasticity. Temperature perception thresholds were assessed above the level of the lesion, using a psychophysical approach based on the ability of the subjects to perceive precisely quantified sensory stimuli (quantitative sensory testing, QST). The data were compared with a control group of healthy subjects, not receiving baclofen. We found that chronic baclofen consumption increased temperature perception thresholds for both cold and warm stimuli in a dose-dependent manner. Temperature perception thresholds did not depend on the level of the lesion nor on the duration of baclofen treatment, suggesting that our finding represent normal GABAB-mediated modulation in spared nervous structures. We conclude that GABAB therefore plays a role in temperature perception in humans.

Does the tibial and sural nerve transection model represent sympathetically independent pain?

Neuropathic pain can be divided into sympathetically maintained pain (SMP) and sympathetically independent pain (SIP). Rats with tibial and sural nerve transection (TST) produce neuropathic pain behaviors, including spontaneous pain, tactile allodynia, and cold allodynia. The present study was undertaken to examine whether rats with TST would represent SMP- or SIP-dominant neuropathic pain by lumbar surgical sympathectomy. The TST model was generated by transecting the tibial and sural nerves, leaving the common peroneal nerve intact. Animals were divided into the sympathectomy group and the sham group. For the sympathectomy group, the sympathetic chain was removed bilaterally from L2 to L6 one week after nerve transection. The success of the sympathectomy was verified by measuring skin temperature on the hind paw and by infra red thermography. Tactile allodynia was assessed using von Frey filaments, and cold allodynia was assessed using acetone drops. A majority of the rats exhibited withdrawal behaviors in response to tactile and cold stimulations after nerve stimulation. Neither tactile allodynia nor cold allodynia improved after successful sympathectomy, and there were no differences in the threshold of tactile and cold allodynia between the sympathectomy and sham groups. Tactile allodynia and cold allodynia in the neuropathic pain model of TST are not dependent on the sympathetic nervous system, and this model can be used to investigate SIP syndromes.

Neurophysiologic and quantitative sensory testing in the diagnosis of trigeminal neuropathy and neuropathic pain

This study investigated the utility of neurophysiologic examination and thermal quantitative sensory testing (QST) in the diagnosis of trigeminal neuropathy and neuropathic pain. Fifty-eight patients (14 men), 34 with sensory deficit within the inferior alveolar nerve (IAN) and 24 within the lingual nerve (LN) distribution, were included. Twenty-six patients (45%) reported neuropathic pain. Patients underwent blink reflex (BR) test and thermal QST; sensory neurography was done to the IAN patients. Results of clinical sensory testing were available from the charts of 48 patients revealing abnormal findings in 77% of the IAN and in 94% of the LN patients. The BR test was abnormal in 41%, neurography in 96%, and QST in 91% of the IAN patients. In the LN group, BR was abnormal in 33%, and QST in 100% of the patients tested. Neurophysiologic tests and QST verified the subjective sensory alteration in all but 2 IAN patients, both with old injuries, and 4 LN patients who did not undergo QST. When abnormal, thermal QST showed elevation of warm and cold detection thresholds (hypo/anesthesia), hypoalgesia was less marked, and heat allodynia was only occasionally present. Contralateral thermal hypoesthesia after unilateral injury was found in 14 patients. It was associated with the occurrence of neuropathic pain (P=0.016). Axonal Abeta afferent damage was less severe in the IAN patients with pain than in those without pain (P=0.012). Neurophysiologic tests and thermal QST provide sensitive tools for accurate diagnosis of trigeminal neuropathy and study of pathophysiological features characteristic to human neuropathic pain.

Complex regional pain syndrome--diagnostic, mechanisms, CNS involvement and therapy

Complex regional pain syndromes (CRPS, formerly reflex sympathetic dystrophy and causalgia) are neuropathic pain conditions of one extremity developing inadequately after a trauma. The initiating trauma affects primarily the extremity, but can also be a central lesion (e.g., spinal cord injury, stroke). CRPS is clinically characterized by sensory, autonomic and motor disturbances. Pathophysiologically there is evidence for functional changes within the central nervous system and for involvement of peripheral inflammatory processes. The sympathetic nervous system plays a key role in maintaining pain and autonomic dysfunction in the affected extremity. After a primary central lesion, secondary peripheral changes in the paretic extremity are suggested to be important in initiating a CRPS. Though there is no diagnostic gold standard, careful clinical evaluation and additional test procedures should lead to an adequate diagnosis. An early diagnosis and an interdisciplinary approach are important for optimal and successful treatment.

Sensory dysfunction in burning mouth syndrome

Our preliminary observations on a small group of burning mouth syndrome (BMS) patients indicated a change in the non-nociceptive, tactile sensory function in BMS and provided evidence for the hypothesis of a neuropathic etiology of BMS. In the present clinical study on a group of 52 BMS patients, we used quantitative sensory tests (QST) in addition to the blink reflex (BR) recordings in order to gain further insight into the neural mechanisms of BMS pain. Based on electrophysiologic findings, the BMS patients could be grouped into four different categories: (1) The results of the BR were suggestive of brainstem pathology or peripheral trigeminal neuropathy in ten (19%) patients. In most of the cases, the abnormalities in the BR seemed to represent subclinical changes of the trigeminal system. (2) Increased excitability of the BR was found in the form of deficient habituation of the R2 component of the BR in 11 (21%) of the patients. Two of these patients also showed signs of warm allodynia in QST. (3) One or more of the sensory thresholds were abnormal indicating thin fiber dysfunction in altogether 35 patients (76%) out of the 46 tested with QST. Thirty-three of these patients showed signs of hypoesthesia. (4) There were only five patients with normal findings in both tests. The present findings with strong evidence for neuropathic background in BMS will hopefully provide insights for new therapeutic strategies.

Quantitative sensory testing in fibromyalgia patients and in healthy subjects: identification of subgroups

OBJECTIVE

To determine perception and pain thresholds in patients with fibromyalgia syndrome and in healthy controls, and to investigate whether patients with fibromyalgia syndrome can be grouped with respect to thermal hyperalgesia and whether these subgroups differ from healthy controls and in clinical appearance.

DESIGN

The authors conducted a quasi-experimental clinical study.

SUBJECTS

Twenty-nine women patients with fibromyalgia syndrome and 21 healthy pain-free age-matched women participated in the study.

METHODS

Quantitative sensory testing using a Thermotest instrument was performed on the dorsum of the left hand. Sleep and pain intensity were rated using visual analog scales.

RESULTS

Cold and heat pain but not perception thresholds differed significantly between patients with fibromyalgia syndrome and healthy subjects. Based on thermal pain thresholds, two subgroups could be identified in fibromyalgia syndrome using cluster analysis.

CONCLUSION

Patients with fibromyalgia syndrome were subgrouped by quantitative sensory testing (i.e., thermal pain thresholds). Subgroups show clinical differences in pain intensities, number of tender points, and sleep quality. Cold pain threshold was especially linked to these clinical aspects.

Vincristine-induced allodynia in the rat

The aims of this study were two-fold: first, to simplify the method for creating a recently described neuropathic pain model in the rat, and second, to evaluate the effects of a number of drugs with analgesic or antihyperalgesic properties, in this model. Continuous intravenous vincristine infusion (1-100 microg kg(-1) day (-1)) for 14 days resulted in a dose dependent tactile allodynia (as measured by von Frey filaments) by 7 days at doses between 30 - 100 microg kg(-1) day (-1), with a hindlimb motor deficit observed at doses greater than 50 microg kg(-1) day (-1). No thermal hyperalgesia was observed. Systemic morphine, lidocaine, mexiletine and pregabalin (given intraperitoneally) produced significant reduction of the allodynia, while tetrodotoxin was without effect. Continuous intravenous infusion of vincristine in rats thus provides a reliable model of chemotherapy induced neuropathy which may be used in defining the mechanism and pharmacology of this clinically relevant condition.

Stress coping strategies in thermal pain sensitive and insensitive healthy subjects

The aim of this study was to investigate stress coping strategies used in relation to heat and cold pain thresholds in healthy subjects. After using the Jalowiec Coping Scale, cold and heat pain thresholds were examined using the Quantitative Somatosensory Test in 47 healthy subjects. The participants were separated into thermal pain sensitive and insensitive groups, based on thermal pain perception. The results showed that subjects sensitive to thermal pain tended to adopt an emotive stress coping style significantly more commonly than the insensitive subjects. Furthermore, women displayed a marked preference for this style compared to men. The conclusion is that emotional stress coping did play a role in the perception of thermal pain in this group of healthy subjects and that clinical nursing interventions need to focus on the relationship between emotion and coping.

Complex regional pain syndromes

Complex regional pain syndromes (CRPS) (formerly reflex sympathetic dystrophy and causalgia) are neuropathic pain conditions that are initiated by an extremity trauma or peripheral nerve lesion. Clinical definition and scientific understanding of CRPS are still evolving; however, both the clinical picture and therapeutic options are significantly influenced by a dysfunction of the sympathetic nervous system. Recent investigations suggest functional central abnormalities and a peripheral inflammatory component in the pathophysiology of CRPS. Interdisciplinary treatment includes physical, pharmacologic, and invasive interventional therapy, as well as stimulation techniques.

An animal model of neuropathic pain employing injury to the sciatic nerve branches

The present study was conducted to develop a new animal model of neuropathic pain employing injury to the distal sciatic nerve branches. Under halothane anesthesia, the tibial, sural, and/or common peroneal nerves were injured and neuropathic pain behaviors were compared among different groups of rats. Different types of injury produced different levels of neuropathic pain. Rats with injury to the tibial and sural nerves showed the most vigorous mechanical allodynia, cold allodynia, and spontaneous pain. These neuropathic pain behaviors were not relieved by functional sympathectomy using guanethidine. The results suggested that injury to the tibial and sural nerves, while leaving the common peroneal nerve intact, can be used as a new animal model of neuropathic pain and that this model represents sympathetically independent pain (SIP). The present animal model is very simple to produce injury and can produce profound and reliable pain behaviors. These features enable the new animal model to be a useful tool in elucidating the mechanisms of neuropathic pain, especially SIP.

Intraventricular infusion of nerve growth factor as the cause of sympathetic fiber sprouting in sensory ganglia

OBJECT

The results of previous clinical trials have indicated that intraventricular infusion of nerve growth factor (NGF) in patients with Alzheimer's disease is frustrated by the appearance of weight loss and diffuse back pain. The present study tested whether NGF induces sympathetic sprouting in sensory ganglia. Such sprouting has been implicated in previous studies as a possible mechanism of sympathetically maintained pain in neuropathic animals.

METHODS

Nineteen Long-Evans rats underwent intraventricular infusion of either artificial cerebrospinal fluid (ACSF; seven animals) or NGF (12 animals). After 14 days of infusion, the sensory ganglia of the trigeminal nerve and the C-2, C-8, T-1, L-4, and L-5 dorsal roots were examined for sympathetic sprouting by using tyrosine hydroxylase immunohistochemical analysis.

CONCLUSIONS

In the animals receiving NGF, 52 of 144 ganglia showed sympathetic fiber sprouting. In the control animals receiving ACSF, only two of 72 ganglia showed minor sympathetic fiber sprouting. A preferential sprouting of sympathetic fibers was demonstrated at lower lumbar ganglia compared with the cervical and thoracic ganglia. The data presented here demonstrate that in the rat intraventricular NGF infusion caused sympathetic sprouting in dorsal root ganglia (p < 0.01). These findings may have importance both for the treatment of Alzheimer's disease and the understanding of neuropathic pain.

Causalgia and reflex sympathetic dystrophy: does the sympathetic nervous system contribute to the generation of pain?

The striking response of causalgia and reflex sympathetic dystrophy (RSD) to sympatholytic procedures together with signs of autonomic nervous system abnormalities suggest that the sympathetic efferent system can generate or enhance pain (sympathetically maintained pain, SMP). This concept is supported by human and animal experiments indicating that sympathetic activity and catecholamines can activate primary afferent nociceptors. Some clinical evidence, however, calls the SMP concept into question and alternative explanations have been advanced. In this review, we describe the clinical features of causalgia and RSD and the evidence for sympatholytic efficacy. The major barrier to proving the SMP concept is that all available sympatholytic procedures are problematic. We conclude that, although the weight of current evidence supports the SMP concept and its relevance to causalgia and RSD, it remains unproven by scientific criteria. More careful adherence to diagnostic criteria and well-controlled trials of sympatholysis are needed to finally settle the issue.

Sympathectomy decreases formalin-induced nociceptive responses independent of changes in peripheral blood flow

The present experiments studied the effect of surgical sympathectomy on mechanical paw withdrawal thresholds and formalin-induced pain behaviors (FIPB) and tested if the effect of sympathectomy on FIPB is dependent on changes in peripheral blood flow. Compared to sham-operated animals, surgical sympathectomy decreased second phase FIPB but did not affect paw withdrawal thresholds to mechanical stimuli. In sympathectomized and sham-operated animals, subcutaneous intraplantar injection of the nonadrenergic vasoconstrictor angiotensin II (20 microl, 1 mM) or the nonadrenergic vasodilator hydralazine (20 microl, 1 mM) prior to formalin injection decreased and increased peripheral blood flow, respectively. In sympathectomized animals, pretreatment with angiotensin II inhibited the increase of peripheral blood flow following formalin injection when compared to animals pretreated with saline or hydralazine. In sham-operated animals, pretreatment with hydralazine or angiotensin II did not alter vasodilation after formalin injection when compared to pretreatment with saline. Pretreatment with vasoactive drugs had no effect on the sympathectomy-induced decrease in FIPB. It is concluded that sympathectomy decreases FIPB by mechanisms that are independent of sympathectomy-induced changes in peripheral blood flow. The formalin test is an easy, reliable model that can be used to study the mechanisms by which the sympathetic nervous system modulates pain processing.

Correlation between autotomy-behavior and current theories of neuropathic pain

The past 10 years have brought several new experimental models with which to study chronic neuropathic pain in animals. Consequently, our knowledge about the mechanisms subserving neuropathic pain in humans has improved. However, the first animal model that was used for studying this type of chronic pain was the autotomy-model which can still be considered as a useful tool for pain studies. The present review assesses some of the similarities and differences between autotomy-model and more recent models of experimental traumatic mononeuropathy. In addition, it considers some of the similarities between the results obtained in clinical studies and in autotomy studies.

Traumatic neuralgias: complex regional pain syndromes (reflex sympathetic dystrophy and causalgia): clinical characteristics, pathophysiological mechanisms and therapy

Complex regional pain syndromes (CPRS) may develop as a disproportionate consequence of a trauma affecting the limbs without (CRPS I, reflex sympathetic dystrophy) or with (CRPS II, causalgia) obvious nerve lesions. The clinical picture of CRPS consists of asymmetrical distal extremity pain, swelling, and autonomic (sympathetic) and motor symptoms. Changes in the peripheral and central somatosensory, autonomic and motor processing, and a pathologic interaction of sympathetic and afferent systems are discussed as underlying pathophysiologic mechanisms. Therapeutic strategies include pharmacologic pain relief, sympatholytic interventions, and rehabilitation.

The cold plate as a test of nociceptive behaviors: description and application to the study of chronic neuropathic and inflammatory pain models

A cold plate apparatus was designed to test the responses of unrestrained rats to low temperature stimulation of the plantar aspect of the paw. At plate temperatures of 10 degrees C and 5 degrees C, rats with either chronic constriction injury (CCI) of the sciatic nerve or complete Freund's adjuvant (CFA) induced inflammation of the hindpaw displayed a stereotyped behavior. Brisk lifts of the treated hindpaw were recorded, while no evidence of other nociceptive behaviors could be discerned. The most consistent responses were obtained with a plate temperature of 5 degrees C in three 5-min testing periods, separated by 10-min intervals during which the animals were returned to a normal environment. Concomitantly to cold testing, the rats were evaluated for their response to heat (plantar test) and mechanical (von Frey hairs) stimuli. In both injury models, while responses to heat stimuli had normalized at 60 days post-injury, a clear lateralization of responses to cold was observed throughout the entire study period. Systemic lidocaine, clonidine, and morphine suppressed responses to cold in a dose-related fashion. At doses that did not affect motor or sensory behavior, both lidocaine and its quaternary derivative QX-314 similarly reduced paw lifts, suggesting that cold hyperalgesia is in part due to peripheral altered nociceptive processing. Clonidine was more potent in CCI then in CFA rats in reducing the response to cold. Paradoxically, clonidine increased the withdrawal latencies to heat in the CCI hindpaw at 40 days and thereafter, at a time when both hindpaws had the same withdrawal latencies in control animals. Morphine was also more potent on CCI than CFA cold responses, indicating that, chronically, CFA-induced hyperalgesia might be opiate resistant. Evidence for tonic endogenous inhibition of cold hyperalgesia was obtained for CFA rats, when systemic naltrexone significantly increased the number of paw lifts; this was not found in rats with CCI. At 60 days, neither morphine nor naltrexone affected cold-induced paw lifting in CFA rats, suggesting that the neuronal circuit mediating cold hyperalgesia in these animals had become opiate insensitive. In conclusion, the cold plate was found to be a reliable method for detecting abnormal nociceptive behavior even at long intervals after nerve or inflammatory injuries, when responses to other nociceptive stimuli have returned to near normal. The results of pharmacological studies suggest that cold hyperalgesia is in part a consequence of altered sensory processing in the periphery, and that it can be independently modulated by opiate and adrenergic systems.

Effects of cutaneous histamine application in patients with sympathetic reflex dystrophy

Thirty-six patients suffering from acute reflex sympathetic dystrophy (RSD) were examined in order to evaluate nociceptive C-fibers. Axon reflex vasodilatation was induced by iontophoresis of histamine and recorded (laser Doppler flux). The strength of concomitant sensation was rated on a visual analogue scale, and the quality was characterized as itching or burning pain. Skin temperature was recorded by infrared thermography. The results were compared with investigations of unaffected limbs of patients and volunteers. The histamine-induced sensation on the symptomatic side was more often burning pain than itching (P < 0.001), and skin temperature was increased on the affected limb (P < 0.001). Axon reflex vasodilatation and the strength of sensations were unaltered. In conclusion, this study rules out a significant deterioration of afferent C-fibers in RSD, but gives evidence of sensitization of nociceptive function. This nociceptive sensitization has to be taken into consideration for effective treatment of RSD.

Nociception from blood vessels is independent of the sympathetic nervous system under physiological conditions in humans

To test the hypothesis that vascular pain depends on sympathetic drive under physiological conditions we studied the effects of both alpha-adrenoceptor stimulation by noradrenaline and alpha-adrenoceptor blockade by phentolamine on the intensity of physicochemically evoked pain from veins in humans. In seven healthy volunteers, a vascularly isolated hand vein segment was perfused continuously with noradrenaline (6 x 10(-9)-6 x 10(-6) M), or phentolamine (1.24 x 10(-4) M). Pain was evoked by intraluminal electrostimulation or by injection of hyperosmolar saline during control perfusion of isoosmolar saline and after each noradrenaline concentration, as well as after perfusion of phentolamine. Subjects rated pain intensity continuously on an electronically controlled visual analogue scale (VAS) between 0% VAS (no pain) and 100% VAS (tolerance maximum). Intravenous electrostimulation as well as hyperosmolar solutions evoked pain in each subject. The intensity of pain was neither influenced by noradrenaline, nor by phentolamine, so that nociception from blood vessels is unlikely to be modulated by the sympathetic nervous system under physiological conditions in humans.

Clinical neurophysiology laboratory tests to assess the nociceptive system in humans

This paper presents some currently available neurophysiological tools that are helpful in the clinical setting to evaluate and document neuropathic disturbances that may be associated with pain. The specific tests described in this discussion are quantitative sensory tests (QSTs), autonomic tests (ATs), microneurography (MCNG), and laser evoked potentials (LEPs). Quantitative sensory testing of the nociceptive system includes the thermal stimulation (TST) and current perception threshold (CPT) tests. The ATs applicable to some patients with pain are sudomotor and vasomotor tests. The quantitative sudomotor axon reflex test (QSART), resting sweat output (RSO), and sympathetic skin response (SSR) are the tests for sudomotor involvement. The vasomotor system is tested by measuring skin temperature (surface thermistor or thermography) at rest and, in some cases, after provocative maneuvers. In addition, MCNG (intraneural recording of single nerve fibers or fascicles of nerves) allows examiners to look directly at muscle and skin sympathetic efferent output in normal subjects without pain or with experimental pain and in patients with neuropathic pain. This technique also provides a means of studying the physiology of primary afferent fibers in persons with neurogenic pain. Recent development of LEPs that incorporate the use of painful infrared laser-induced stimuli allow selective study of the nociceptive system, both the central and peripheral portions.

Peripheral alpha-adrenoreceptors are involved in the development of capsaicin induced ongoing and stimulus evoked pain in humans

While the sympathetic nervous system seems to be involved in some pain states, the mechanisms linking the sensory and sympathetic nervous system are unclear. In this study the possible involvement of peripheral alpha-adrenoreceptors in the development of capsaicin induced ongoing pain and mechanical hypersensitivity was examined in humans. Intradermal capsaicin injections in the volar aspect of the arm gave rise to ongoing burning pain and dysesthesia as well as mechanical hypersensitivity. Ongoing pain and pain evoked by von Frey filament stimulation was rated on a numerical rating scale after intradermal capsaicin injection. The area of skin in which von Frey filament stimulation evoked pain was measured. A subcutaneous injection of phentolamine (alpha-adrenoreceptor antagonist) on one side and saline on the other side prior to the capsaicin injection was done to evaluate the role of the peripheral alpha-adrenoreceptors in development of capsaicin induced sensory symptoms and signs. Significantly less ongoing and evoked pain developed on the phentolamine injected side compared to the saline side, the latter in the area adjacent to the capsaicin injection (primary zone) and well outside the area of flare (secondary zone). The area in which pain could be evoked on the phentolamine injected side was restricted to the area of flare and was significantly smaller than on the saline injected side. Mechanical stimulation gave rise to aftersensation and radiation of pain on the saline injected side in all subjects but only in one case on the phentolamine injected side. Peripheral alpha-adrenoreceptors thus seem to be involved in functional changes of primary afferents which contribute to ongoing pain and mechanical stimulus evoked pain.

Reflex sympathetic dystrophy: skin blood flow, sympathetic vasoconstrictor reflexes and pain before and after surgical sympathectomy

To examine the pathophysiological mechanisms of vascular disturbances and to assess the role of the sympathetic nervous system, 12 patients with reflex sympathetic dystrophy (RSD) of the hand were studied using laser Doppler flowmetry. Cutaneous blood flow, skin resistance and skin temperature were measured at the affected and contralateral hands. Sympathetic vasoconstrictor reflexes were induced bilaterally by deep inspiration. Four patients were treated with unilateral surgical sympathectomy and pain and vascular changes were documented in follow-up investigations. (1) After acclimatization in cold environment (< or = 18 degrees C) blood flow and skin temperature were considerably lower on the affected side in 10 patients. No additional vasoconstrictor reflexes could be elicited. (2) After acclimatization in warm environment (22-24 degrees C) blood flow and skin temperature demonstrated no side differences in all cases. Vasoconstrictor responses were the same on both sides. (3) After sympathectomy vasoconstrictor reflexes were absent. Skin resistance was considerably higher on the affected side. In the first 4 weeks the affected hand was warmer and blood flow was higher compared with the healthy side. Thereafter, skin temperature and perfusion slowly decreased and the affected hand turned from warm to cold. Very regular high amplitude vasomotion waves occurred unilaterally. There were no signs of reinnervation. Two patients had long-term pain relief. We conclude as follows. (1) Side differences in skin temperature and blood flow are no static descriptors in RSD. They are dynamic values depending critically on environmental temperature. Therefore, they have to be interpreted with care when defining reliable diagnostic criteria. (2) Vascular disturbances in RSD are not due to constant overactivity of sympathetic vasoconstrictor neurons. Changes in vascular sensitivity to cold temperature and circulating catecholamines may be responsible for vascular abnormalities. Alternatively, RSD may be associated with an abnormal (side different) reflex pattern of sympathetic vasoconstrictor neurons due to thermoregulatory and emotional stimuli generated in the central nervous system. (3) After sympathectomy, denervation supersensitivity of blood vessels and intense vasomotion may be associated with recurrence of pain in some patients.

Biochemical aspects of chronic pain and its relationship to treatment

This review presents an overview of the neurotransmitters and neuromodulators involved in acute and chronic pain. Although there is little evidence that the neuronal pathways differ in the two types of pain, it is clear that different transmitters or receptor types are involved in hyperalgesia and chronic pain. While most attention has been focussed on spinal processes, it is apparent that some types of chronic pain have both a peripheral and a supraspinal component. The presently available drugs are probably adequate for acute pain, but the treatment of chronic pain may need to be tailored to the individual patient.

Scoliosis as the first sign of a cystic spinal cord lesion

We reviewed the cases of ten patients with scoliosis as the first sign of a cystic spinal cord lesion with the aim of identifying and studying early patient and curve characteristics. All patients were examined with magnetic resonance (MR) imaging of the brain and spinal cord and quantitative thermal testing (QTT). The mean Cobb angle was 22 degrees and the curves were right thoracic in seven patients, left thoracic in two, and left lumbar in one, when first seen for scoliosis. In six patients the cystic lesion was found in routine screening for syringomyelia, which is performed in all cases of congenital and juvenile scoliosis and in adolescent scoliosis before bracing. In four patients, it took up to 17 years following the initial diagnosis of scoliosis before neurologic deterioration warranted MR imaging, disclosing two Chiari I associated syrinxes and two cystic spinal cord tumors. QTT revealed a subclinically decreased sensation in two of the patients with no findings other than scoliosis. It also verified the decreased sensation in all patients in whom neurologic deterioration had complicated the clinical course of their scoliosis. More frequent spinal MR screening of patients with supposed juvenile or adolescent idiopathic scoliosis is indicated, regardless of curve type, to exclude a neurogenic cause. QTT documents subclinical as well as overt decreased sensation, and is valuable in the serial follow-up of these patients to monitor the progress or the response to treatment of the cystic lesion.

Noradrenaline-evoked pain in neuralgia

We have tested the effects of cutaneous application of noradrenaline in 35 patients presenting with neuropathic pain. Depending on the outcome of sympatholytic interventions the patients were considered to have sympathetically maintained pain (SMP; n = 25) or sympathetically independent pain (SIP; n = 10). Iontophoretic application or cutaneous injection of noradrenaline into symptomatic skin aggravated pain and mechanical or thermal hyperalgesia in 7/25 SMP patients. Results from differential nerve blocks suggested that noradrenaline-induced ongoing pain and heat hyperalgesia were signalled by unmyelinated afferents, while touch-evoked pain and cold hyperalgesia were signalled by myelinated afferents. In none of the remaining 18/25 SMP patients, 10 SIP patients or 18 normal subjects did application of noradrenaline result in any appreciable increase of pain. A follow-up of 12 patients (initially 9 SMP, 3 SIP) after 12-16 years showed that one individual (previously SMP) was healthy, while 3 patients still suffered from SMP and 8 from SIP. Of the 5 SMP patients who had noradrenaline-induced pain at the initial examination, only 1 SMP patient still responded to noradrenaline with pain and hyperalgesia. Three other patients had changed to SIP and 1 individual was healthy. None of these 4 and none of the 7 initially noradrenaline-unresponsive patients experienced pain to the noradrenaline challenge at follow-up. Thus, cutaneous noradrenaline application can aggravate the pain in some, but not all SMP patients. THe abnormal noradrenaline reaction can change over time as can the pain relieving effects of sympatholytic therapy.

[Chronic, sympathetically maintained pain syndrome after mild lesion of the brachial plexus-a case report.]

The present article is a case report on a chronic sympathetically maintained pain syndrome following a mild lesion of the brachial plexus. Apart from slight motor and sensory disturbances, which disappeared within a few months, no autonomic, motor or sensory deficit remained. Spontaneous pain and a remarkable allodynia in the region of the left upper quadrant, always without the left hand developed. The pain syndrome obviously extended beyond the region of the primary affected nerve. In the climax of the pain attacks it became manifest like a mirror reflexion on the opposite side. The diagnostic and therapeutic problems that occurred during these years and the dependency of the pain attacks on exterior influences are evaluated.

Effects of regional intravenous guanethidine in patients with neuralgia in the hand; a follow-up study over a decade

A study on the effect of regional intravenous (i.v.) guanethidine blockade (RGB) was done over a 10 years period in patients with post-traumatic neuralgia. Seven patients, investigated with quantitative sensory testing (QST) before and after RGB between 1979 and 1982, were reinvestigated in the period 1990-1992. In addition to the RGB, 6 patients were subjected to a placebo procedure with tourniquet inflation and i.v. injection of saline at follow-up. All patients had ongoing pain and stimulus-induced pain (hyperalgesia) in one hand. The QST was done by an independent observer who was blind with regard to the different treatments. Three patients with long-lasting relief of ongoing pain and significant reduction of stimulus-induced pain after RGB, were classified as having sympathetically maintained pain (SMP) both at 1st examination and at follow-up 10 years later. In 2 patients, classified as having sympathetically independent pain (SIP), neither the ongoing pain nor the hyperalgesia improved at any occasion. Two patients, classified as SMP in 1979-1982, changed to SIP at follow-up. Placebo had no significant effect on the hyperalgesia to heat, cold or vibration in the 6 SMP/SIP patients tested. In conclusion, some patients with neuralgia, diagnosed 17-26 years ago, still had long-lasting pain relief from an i.v. RGB, whereas others consistently had no such effect. None obtained long-lasting pain relief from placebo. This supports the notion that different pathophysiological mechanisms are involved in post-traumatic neuralgia.

Reflex sympathetic dystrophy following arterial blood gas sampling in the intensive care setting

A 54-year-old woman developed signs and symptoms consistent with reflex sympathetic dystrophy in her left upper extremity following arterial puncture. Diagnosis was confirmed by bone scan, and sympathetic blockade with intravenous regional bretylium completely relieved her severe, intractable pain.

Involvement of the sympathetic postganglionic neuron in capsaicin-induced secondary hyperalgesia in the rat

The involvement of the sympathetic postganglionic neuron in secondary hyperalgesia was evaluated using a model of secondary hyperalgesia induced by a small intradermal injection of capsaicin in the rat, a procedure known to produce mechanical hyperalgesia/allodynia in humans. Capsaicin injection into the glabrous skin of the hind paw led to increased sensitivity to mechanical stimulation with von Frey filaments at the injection site (i.e. primary hyperalgesia) as well as in an area of the hind paw remote from the site of injection (i.e. secondary hyperalgesia). Surgical removal of the sympathetic postganglionic neurons innervating the hind paw plantar skin before the capsaicin injection prevented secondary hyperalgesia. However, decentralization of the sympathetic postganglionic neurons subserving the hind paw did not effect secondary hyperalgesia. Phentolamine, an alpha-adrenergic receptor antagonist, as well as prazosin, an alpha 1-adrenergic receptor antagonist, given systemically, both blocked the development of secondary hyperalgesia. Yohimbine, an alpha 2-adrenergic receptor antagonist, was without effect. Prazosin also blocked the development of secondary hyperalgesia when given intradermally at the site of capsaicin injection. Activation of C-fibres with capsaicin induces secondary hyperalgesia, which is sympathetic postganglionic neuron-dependent. This sensory-sympathetic interaction is, however, independent of preganglionic sympathetic outflow and seems to be mediated by an alpha 1-adrenergic mechanism. Sensory-sympathetic interaction appears to take place in the area of capsaicin-induced C-fibre nociceptor activation.

Sensory and sympathetic contributions to nerve injury-induced sensory abnormalities in the rat

Peripheral neuropathy can be associated with a variety of symptoms, including spontaneous unpleasant sensations and pain, as well as increased sensitivity to sensory stimuli. A peripheral neuropathy model involving an L5 spinal nerve lesion in male rats has been used to gain insight into the mechanisms that underlie symptoms that develop after nerve injury. This model was used to study the involvement of sensory fibres, the sympathetic postganglionic neuron and the role of nerve growth factor in the induction and maintenance of altered sensory function in the nerve territory of the intact L4 spinal nerve. Sensory testing was done with calibrated von Frey filaments and a radiant heat apparatus [Hargreaves K. et al. (1988) Pain 32, 77-88] and the occurrence of abnormal spontaneous behaviour was recorded. L5 spinal nerve resection produced increased mechanical and heat sensitivity as well as abnormal spontaneous behaviours. Surgical sympathectomy at the L5 but not at the L4 spinal nerve level alleviated all sensory abnormalities. However, a lesion of preganglionic fibres to the L5 level had no significant effect on sensory abnormalities. Thus, sympathetic postganglionic neurons at the level of spinal nerve injury can contribute to neuropathy symptoms independent of input from preganglionic neurons. Postganglionic sympathetic nerve crush alone led to increased mechanical sensitivity but not to increased heat sensitivity nor to abnormal spontaneous behaviour, further emphasizing the role of sympathetic postganglionic neuron changes for the development of increased mechanical sensitivity. An L5 spinal nerve resection in rats treated neonatally with capsaicin induced increased mechanical sensitivity which was slower in onset and lower in magnitude than that in untreated littermates and was abolished by postganglionic sympathectomy. Nerve growth factor perfused onto the cut L5 spinal nerve also markedly delayed the onset of increased mechanical sensitivity. Two pathophysiological mechanisms leading to central changes may be necessary to produce altered sensations in this model: (i) ongoing activity in C-fibres, independent of sympathetic postganglionic neuron activity and (ii) activity in sensory fibres modulated by a sensory-sympathetic interaction in the injured spinal nerve or dorsal root ganglion. The sympathetic postganglionic neuron contribution is independent of preganglionic sympathetic outflow from the central nervous system, suggesting a novel mechanism by which sympathetic efferent terminals can regulate sensory fibre activity. A contribution of a loss of neurotrophic factors to the sympathetic postganglionic neuron following nerve lesion is also suggested to contribute to the symptoms induced by the spinal nerve lesion.

Alpha 1-adrenoceptor-mediated sympathetically dependent mechanical hyperalgesia in the rat

The model of rolipram (a type IV phosphodiesterase inhibitor) induced prolongation (> 3 days) of the mechanical hyperalgesia produced by the intradermal injection of prostaglandin E2 in the hairy skin of the hindpaw of the rat, measured by the Randall-Selitto paw-withdrawal test, was employed to study mechanisms involved in the contribution of the sympathetic postganglionic neuron to mechanical hyperalgesia. Lumbar surgical sympathectomy prevented rolipram-induced prolongation of prostaglandin E2 hyperalgesia. Decentralization of sympathetic postganglionic neurons innervating the hindpaw did not, however, effect rolipram-induced prolongation of prostaglandin E2 hyperalgesia. Phentolamine, an alpha-adrenoceptor antagonist, and prazosin, an alpha 1-selective adrenoceptor antagonist, when given systemically or intradermally at the site of injection of prostaglandin E2 and rolipram, blocked rolipram-induced prolongation of prostaglandin E2 hyperalgesia. Intrathecal administration of phentolamine and prazosin were, however, without effect on rolipram-induced prolongation of prostaglandin E2 hyperalgesia. Yohimbine, an alpha 2-adrenoceptor antagonist given systemically, intradermally or intrathecally also did not produce any alteration in rolipram-induced prolongation of prostaglandin E2 hyperalgesia. We propose that sympathetic postganglionic neurons are involved in rolipram-induced prolongation of prostaglandin E2 hyperalgesia and that this form of sympathetically dependent hyperalgesia, which is independent of activity in preganglionic sympathetic neurons, is mediated by a peripheral alpha 1-adrenergic mechanism.

A loose ligature-induced mononeuropathy produces hyperalgesias mediated by both the injured sciatic nerve and the adjacent saphenous nerve

An experimental mononeuropathy was produced in rats by unilateral loose ligation of the sciatic nerve, with a contralateral sham surgery. Repeated bilateral sensory testing was performed over time to investigate any threshold differences between the loose ligature side and the contralateral control side. A prolonged reduction in the mean withdrawal threshold to heat was observed on the loose ligature side over the medial dorsum of the hindpaw (MDH), and over the plantar surface of the hindpaw (PSH). Following loose ligature there was also a significant reduction in the von Frey fiber withdrawal thresholds over the lateral dorsum of the hindpaw (LDH) and the medial dorsum of the hindpaw (MDH). In a second experiment the saphenous nerves were transected bilaterally in rats who had an earlier unilateral loose sciatic ligation. The heat hyperalgesia that had been previously observed over the MDH was abolished, and no withdrawal response could be elicited with the largest von Frey fiber over the MDH, indicating that the MDH hyperalgesia induced by sciatic loose ligature was mediated by the saphenous nerve. This adjacent neuropathic hyperalgesia (ANH) resembles the saphenous mediated ANH observed over the MDH following sciatic transection, follows the same temporal course of onset, and may share a similar pathogenesis. The heat threshold over the PSH and the pressure threshold over the LDH were unaffected by the bilateral saphenous transection, demonstrating that following loose sciatic ligation both of these thresholds are mediated by the sciatic nerve.

Human microneurography and intraneural microstimulation in the study of neuropathic pain

Psychophysical experiments in combination with microneurography and intraneural microstimulation in awake human subjects have yielded some useful information on somatosensory functions under normal and pathologic conditions. Normally, pain is signaled by nociceptive afferents, and tactile sensations are evoked from activation of low-threshold mechanoreceptors. Following tissue injury, nociceptors are sensitized, and their enhanced responsiveness correlates with hyperalgesia to heat and in some cases to mechanical stimuli. In addition, ongoing activity in sensitized nociceptive afferents may lead to central sensitization in such a way that normally nonpainful gentle stroking the skin evokes pain from activation of low-threshold mechanoreceptors. This particular change in signal processing in the central nervous system is restored when the ongoing nociceptive input is interrupted, whereas other forms of central sensitization can outlast the duration of the nociceptive input.

Effects of sympathectomy on a rat model of peripheral neuropathy

The aim of this study was to determine the effects of sympathectomy on our previously developed animal model for neuropathic pain. The neuropathy was produced by a unilateral tight ligation of the L5 and L6 spinal nerves in 81 rats, all of which showed a marked increase in frequency of paw lifting in response to innocuous mechanical stimuli and a shortened latency of paw withdrawal in response to noxious radiant heat stimuli on the affected limb. We interpreted these as behavioral signs of mechanical allodynia and heat hyperalgesia. Surgical sympathectomy was performed by removing the sympathetic chain bilaterally from the L2 to L6 levels at 1 week prior to and 1, 3 and 5 weeks after nerve injury. In addition, the effect of sympathetic block was tested by systemically injecting guanethidine or phentolamine. Surgical sympathectomy relieved the signs of both mechanical allodynia and heat hyperalgesia. The effect of sympathectomy for mechanical allodynia is estimated to be almost fully expressed within 30 min after the operation. Sympathetic block by chemical agents reversibly relieved the mechanical allodynia. These data suggest that the rats in our model exhibit behavioral signs of neuropathic pain that are sympathetically maintained.

Mechanical hyperalgesia in streptozotocin-diabetic rats is not sympathetically maintained

It has been suggested that the mechanism underlying the pain that occurs in patients with diabetic neuropathy may be similar to that mediating sympathetically maintained pain (SMP), such as occurs in patients with reflex sympathetic dystrophy. To evaluate this suggestion we have examined a model of diabetes mellitus, the streptozotocin-diabetic (STZ-D) rat, for features characteristic of SMP. We demonstrate that the decrease in nociceptive threshold observed in the STZ-D rat is not attenuated by chemical sympathectomy nor exacerbated by intradermal injection of norepinephrine (NE). In addition, the NE content is markedly decreased in the skin of the STZ-D rat. These results suggest that altered nociceptive thresholds associated with diabetic neuropathy are not sympathetically maintained.