The interpretation of pain relief and sensory changes following sympathetic blockade

Correlation Between Temperature Rise after Sympathetic Block and Pain Relief in Patients with Complex Regional Pain Syndrome

OBJECTIVE

Determine the correlation between post-sympathetic block pain temperature change, and immediate and intermediate-term pain relief.

DESIGN

Retrospective analysis.

SETTING

Academic setting.

SUBJECTS

79 pts with CRPS who underwent sympathetic block.

METHODS

Pre- and post-block temperatures in the affected extremity, and pain scores immediately (based on 6-hour pain diary) post-block and at the intermediate-term 4-8-week follow-up were recorded. Post-block pain reductions of 30-49% and ≥ 50% were designated as partially sympathetically-maintained pain (SMP) and SMP. A decrease in pain score ≥ 2-points lasting ≥ 4 weeks was considered a positive intermediate-term outcome for sympathetic block.

RESULTS

A weak correlation was found between immediate-term pain relief and the extent of temperature rise for the cohort (R = 0.192, P = 0.043). Greater immediate-term pain reduction was reported among patients who experienced ≥ 7.5° C temperature increase (mean 4.1, 95% CI [3.33, 4.76]) compared to those who experienced < 2° C (2.3, 95% CI [1.36, 3.31]) and ≥ 2° C x < 7.5° C (2.9, 95% CI [1.8; 3.9]; P = 0.036). The correlations between temperature increase and intermediate-term pain score reduction at 4-8 weeks (R = 0.052, P = 0.329), and between immediate and intermediate-term pain relief (R = 0.139, P = 0.119) were not statistically significant.

CONCLUSIONS

A weak correlation was found for those who experienced greater temperature increases post-block to experience greater immediate pain relief. Higher temperature increase cutoffs than are typically used may be necessary to determine whether a patient with CRPS has SMP.

Effects of Stellate Ganglion Block on Analgesia Produced by Cervical Paravertebral Block as Established by Quantitative Sensory Testing: A Randomized Controlled Trial

Objective

To use quantitative sensory testing (QST) to assess whether a stellate ganglion block (SGB) modulates the analgesia induced by cervical paravertebral block (CPVB).

Design

A prospective double-blind randomized controlled trial.

Setting

Department of Anesthesia, Antwerp University Hospital, October 2011 to December 2015.

Subjects

Twenty-eight adults scheduled for arthroscopy of a nonfractured shoulder were enrolled.

Methods

Participants were randomly assigned to receive either single CPVB (5 mL of levobupivacaine 0.5%) or combined CPVB + SGB (5 mL and 3 mL of levobubivacaine 0.5%, respectively). The detection thresholds for cold/warm sensations and cold/heat pain were established using thermal QST on the C4-C7 dermatomes before local anesthetic infiltration and at 0.5, 6, 10, and 24 hours thereafter. Our primary outcome was the time course of QST thresholds for the different neurosensitive/nociceptive modalities. As secondary and tertiary outcomes, we evaluated the degree of motor block and the time to first administration of rescue analgesics.

Results

We randomized 20 patients. There were no significant differences in the detection thresholds for the neurosensitive/nociceptive modalities, motor block, or timing for rescue analgesics between the groups (P = 0.15-0.94). All patients with CPVB + SGB exhibited Horner's signs, whereas patients in the CPVB group did not exhibit these signs; however, this does not exclude sympathetic block.

Conclusions

We were unable to demonstrate any analgesic benefit of CPVB + SGB in arthroscopic shoulder surgery. It is therefore not unreasonable to suppose that pain from soft tissue injuries without bony lesions is transmitted mainly by somatic nerves with no or only minimal involvement of the sympathetic nervous system.

Local anaesthetic sympathetic blockade for complex regional pain syndrome

BACKGROUND

This review is an update of a previously published review in the Cochrane Database of Systematic Reviews, 2005, Issue 4 (and last updated in the Cochrane Database of Systematic Reviews, 2013 issue 8), on local anaesthetic blockade (LASB) of the sympathetic chain to treat people with complex regional pain syndrome (CRPS).

OBJECTIVES

To assess the efficacy of LASB for the treatment of pain in CRPS and to evaluate the incidence of adverse effects of the procedure.

SEARCH METHODS

For this update we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2015, Issue 9), MEDLINE (Ovid), EMBASE (Ovid), LILACS (Birme), conference abstracts of the World Congresses of the International Association for the Study of Pain, and various clinical trial registers up to September 2015. We also searched bibliographies from retrieved articles for additional studies.

SELECTION CRITERIA

We considered randomised controlled trials (RCTs) that evaluated the effect of sympathetic blockade with local anaesthetics in children or adults with CRPS compared to placebo, no treatment, or alternative treatments.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. The outcomes of interest were reduction in pain intensity, the proportion who achieved moderate or substantial pain relief, the duration of pain relief, and the presence of adverse effects in each treatment arm. We assessed the evidence using GRADE (Grading of Recommendations Assessment, Development and Evaluation) and created a 'Summary of findings' table.

MAIN RESULTS

We included an additional four studies (N = 154) in this update. For this update, we excluded studies that did not follow up patients for more than 48 hours. As a result, we excluded four studies from the previous review in this update. Overall we included 12 studies (N = 461), all of which we judged to be at high or unclear risk of bias. Overall, the quality of evidence was low to very low, downgraded due to limitations, inconsistency, imprecision, indirectness, or a combination of these.Two small studies compared LASB to placebo/sham (N = 32). They did not demonstrate significant short-term benefit for LASB for pain intensity (moderate quality evidence).One small study (N = 36) at high risk of bias compared thoracic sympathetic block with corticosteroid and local anaesthetic versus injection of the same agents into the subcutaneous space, reporting statistically significant and clinically important differences in pain intensity at one-year follow-up but not at short term follow-up (very low quality evidence).Of two studies that investigated LASB as an addition to rehabilitation treatment, the only study that reported pain outcomes demonstrated no additional benefit from LASB (very low quality evidence).Eight small randomised studies compared sympathetic blockade to various other active interventions. Most studies found no difference in pain outcomes between sympathetic block versus other active treatments (low to very low quality evidence).One small study compared ultrasound-guided LASB with non-guided LASB and found no clinically important difference in pain outcomes (very low quality evidence).Six studies reported adverse events, all with minor effects reported.

AUTHORS' CONCLUSIONS

This update's results are similar to the previous versions of this systematic review, and the main conclusions are unchanged. There remains a scarcity of published evidence and a lack of high quality evidence to support or refute the use of local anaesthetic sympathetic blockade for CRPS. From the existing evidence, it is not possible to draw firm conclusions regarding the efficacy or safety of this intervention, but the limited data available do not suggest that LASB is effective for reducing pain in CRPS.

Local anaesthetic sympathetic blockade for complex regional pain syndrome

BACKGROUND

This is an update of the original Cochrane review published in The Cochrane Library, 2005, Issue 4, on local anaesthetic blockade (LASB) of the sympathetic chain used to treat complex regional pain syndrome (CRPS).

OBJECTIVES

To assess the efficacy of LASB for the treatment of pain in CRPS and to evaluate the incidence of adverse effects of the procedure.

SEARCH METHODS

We updated searches of the Cochrane Pain, Palliative and Supportive Care Group Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL) on the Cochrane Library (Issue 11 of 12, 2012), MEDLINE (1966 to 22/11/12), EMBASE (1974 to 22/11/12), LILACS (1982 to 22/11/12), conference abstracts of the World Congresses of the International Association for the Study of Pain (1995 to 2010), and various clinical trial registers (inception to 2012). We also searched bibliographies from retrieved articles for additional studies.

SELECTION CRITERIA

We considered for inclusion randomised controlled trials (RCTs) that evaluated the effect of sympathetic blockade with local anaesthetics in children or adults with CRPS.

DATA COLLECTION AND ANALYSIS

The outcomes of interest were reduction in pain intensity levels, the proportion who achieved moderate or substantial pain relief, the duration of pain relief, and the presence of adverse effects in each treatment arm.

MAIN RESULTS

We included an additional 10 studies (combined n = 363) in this update. Overall we include 12 studies (combined n = 386). All included studies were assessed to be at high or unclear risk of bias.Three small studies compared LASB to placebo/sham. We were able to pool the results from two of these trials (intervention n = 23). Pooling did not demonstrate significant short-term benefit for LASB (in terms of the risk of a 50% reduction of pain scores).Of two studies that investigated LASB as an addition to rehabilitation treatment, the only study that reported pain outcomes demonstrated no additional benefit from LASB.Eight small randomised studies compared sympathetic blockade to another active intervention. Most studies found no difference in pain outcomes between sympathetic block and other active treatments.Only five studies reported adverse effects, all with minor effects reported.

AUTHORS' CONCLUSIONS

This update has found similar results to the original systematic review. There remains a scarcity of published evidence to support the use of local anaesthetic sympathetic blockade for CRPS. From the existing evidence it is not possible to draw firm conclusions regarding the efficacy or safety of this intervention but the limited data available do not suggest that LASB is effective for reducing pain in CRPS.

Lumbar sympathetic blockade in children with complex regional pain syndromes: a double blind placebo-controlled crossover trial

BACKGROUND

Sympathetic blockade is used in the management of complex regional pain syndromes in children, but there are no data on the efficacy or mechanism(s) by which it produces pain relief. The purpose of this study is to compare the efficacy of lidocaine administered by lumbar sympathetic to IV route.

METHODS

Under general anesthesia, children with unilateral lower limb complex regional pain syndromes received catheters along the lumbar sympathetic chain. In a double-blind placebo-controlled crossover design, patients received IV lidocaine and lumbar sympathetic saline or lumbar sympathetic lidocaine and IV saline. Spontaneous and evoked pain ratings and sensory thresholds were assessed before and after these two lidocaine/saline doses and between routes of lumbar sympathetic blockade and IV.

RESULTS

Twenty-three patients, ages 10-18 yr, were enrolled. There was evidence for reduction of mean pain intensity of allodynia to brush (mean -1.4, 95% confidence interval [CI] -2.5 to -0.3) and to pinprick temporal summation (mean -1.3, 95% CI -2.5 to -0.2) with lidocaine treatment via the lumbar sympathetic blockade compared to IV route. Lumbar sympathetic blockade also produced significant reduction in pain intensity compared to pretreatment values of allodynia to brush, pinprick and pinprick temporal summation and verbal pain scores. IV lidocaine did not produce significant changes in spontaneous and evoked pain intensity measurements compared to pretreatment values. There were no carryover effects as assessed by route-by-period interaction.

CONCLUSIONS

Under the conditions of this study, the results provide some direct evidence that a component of pain may be mediated by abnormal sympathetic efferent activity.

Pharmacologic management of complex regional pain syndrome

Few randomized controlled trials of oral pharmacotherapy have been performed in patients with complex regional pain syndrome (CRPS). The prevalence of CRPS is uncertain. Severe and advanced cases of CRPS are easily recognized but difficult to treat and constitute a minority compared with those who meet minimum criteria for the diagnosis. Unsettled disability or liability claims limit pharmaceutical industry interest in the disorder. Many studies are small or anecdotal, or are reported on only via posters at meetings. Targeting the process of bone resorption with bisphosphonate-type compounds such as calcitonin, clodronate, and alendronate has shown efficacy in three published randomized controlled trials. Intravenous phentolamine has been studied both alone and in comparison to intravenous regional blockade or stellate ganglion block. Steroids continue to be administered by multiple routes without large-scale placebo-controlled trials. Topical medications have received little attention. There has been considerable interest in the use of thalidomide and TNF-alpha blockers for CRPS, but no published controlled trials as of yet. Numerous other oral drugs, including muscle relaxants, benzodiazepines, antidepressants, anticonvulsants, and opioids, have been reported on anecdotally. Some therapies have been the subject of early controlled studies, without subsequent follow-up (eg, ketanserin) or without an analogous well-tolerated and equally effective oral treatment (eg, intravenous ketamine). Gabapentin, tricyclic antidepressants, and opioids have been proven effective for chronic pain in disorders other than CRPS. Each has shown a broad enough spectrum of analgesic activity to be cautiously recommended for treatment of CRPS until adequate randomized controlled trials settle the issue. The relative benefit of oral medications compared with the widely used treatments of intensive physical therapy, nerve blocks, sympathectomy, intraspinally administered drugs, and neuromodulatory therapies (eg, spinal cord stimulation) remains uncertain. In summary, treatment of CRPS has received insufficient study and remains largely empirical.

Local anesthetic sympathetic blockade for complex regional pain syndrome

BACKGROUND

Local anesthetic blockade of the sympathetic chain is widely used to treat reflex sympathetic dystrophy (RSD) and causalgia. These two pain syndromes are now conceptualized as variants of a single entity: complex regional pain syndrome (CRPS). A recent meta-analysis of the topic has been published. However, this study only evaluated studies in English language and therefore it could have overlooked some randomized controlled trials.

OBJECTIVES

This systematic review had three objectives: to determine the likelihood of pain alleviation after sympathetic blockade with local anesthetics in the patient with CRPS; to assess how long any benefit persists; and to evaluate the incidence of adverse effects of the procedure.

SEARCH STRATEGY

We searched the Cochrane Pain, Palliative and Supportive Care Register, the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, LILACS, and conference abstracts of the World Congresses of the International Association for the Study of Pain. Bibliographies from retrieved articles were also searched for additional studies.

SELECTION CRITERIA

We considered for inclusion randomized controlled trials that evaluated the effect of sympathetic blockade with local anesthetics in children or in adult patients to treat RSD, causalgia, or CRPS.

DATA COLLECTION AND ANALYSIS

The outcomes of interest were the number of patients who obtained at least 50% of pain relief shortly after sympathetic blockade (30 minutes to 2 hours) and 48 hours or later. We also assessed the presence of adverse effects in each treatment arm. A random effects model was used to combine the studies.

MAIN RESULTS

Two small randomized double blind cross over studies that evaluated 23 subjects were found. The combined effect of the two trials produced a relative risk (RR) to achieve at least 50% of pain relief 30 minutes to 2 hours after the sympathetic blockade of 1.17 (95% CI 0.80-1.72). It was not possible to determine the effect of sympathetic blockade on long-term pain relief because the authors of the two studies evaluated different outcomes.

AUTHORS' CONCLUSIONS

This systematic review revealed the scarcity of published evidence to support the use of local anesthetic sympathetic blockade as the 'gold standard' treatment for CRPS. The two randomized studies that met inclusion criteria had very small sample sizes, therefore, no conclusion concerning the effectiveness of this procedure could be drawn. There is a need to conduct randomized controlled trials to address the value of sympathetic blockade with local anesthetic for the treatment of CRPS.

A novel technique for experimental stellate ganglion block in rats

A stellate ganglion block (SGB) is routinely performed in a clinical setting for the treatment of sympathetically maintained pain syndromes. However, the cardiovascular effects of SGB have not been well defined. The purpose of the present study was to develop a new technique of SGB in a rat model. Our new technique of SGB is a posterior percutaneous approach and uses the cartilaginous process of the C7 spinous process as a landmark. Twenty-six Sprague-Dawley female rats were divided into six groups. Group I (n = 4) underwent right sided SGB, Group II (n = 5) underwent left-sided SGB, and Group III (n = 5) underwent bilateral SGB using bupivacaine 0.25%. Three additional sham groups (n = 4 in each group) served as controls to each of the three treatment groups. Ipsilateral eyelid droop (ptosis) was observed in all animals that underwent SGB with bupivacaine. Heart rate decreased significantly for up to 45 min after bilateral SGB compared with control groups. However, this value did not change in rats after unilateral SGB. In 9 additional rats, we evaluated the accuracy of SGB by injecting methylene blue to stain the right (n = 3), left (n = 3), and bilateral SGB (n = 3). At autopsy, 11 of 12 SG were stained post-methylene blue injection. We conclude from our study that our new approach, posterior percutaneous SGB is a reliable technique that can be used for further studies.

IMPLICATIONS

We describe a new technique for stellate ganglion block in rats that may be used in future studies to investigate the role of cervical sympathetic nervous system (especially the stellate ganglion) in regulating sympathetically maintained pain and myocardial function.

Outcome Prediction Following Sympathetic Block for Complex Regional Pain Syndrome

Evidence for the efficacy of sympathetic blocks as either diagnostic or therapeutic tools in complex regional pain syndrome (CRPS) remains anecdotal. Systematic evaluation has been confounded by inconsistent terminology, difficulties in objectively quantifying physical findings, and failure to control for co-morbid psychological factors. This study examines the relative contribution of physical and psychometric features as prospective predictors of outcome following sympathetic block in the treatment of CRPS. Twenty patients with CRPS characterized by mechanical allodynia and vasomotor/sudomotor disturbance were treated with sympathetic blocks. Long-term outcome was assessed at > 6 months following the last treatment using a mailed questionnaire. Pain relief and functional improvement were negatively influenced by anxiety (P < 0.001). When the improvement in the initial visual analog for pain (VAS) was 50% or greater following "diagnostic" sympathetic block, the percent improvement was highly correlated with improvement at long-term follow-up (P < 0.001). Higher "sensitivity" scores on the Neuropathic Pain Scale (P < 0.001), C fiber allodynia (P < 0.01) and Adelta-fiber allodynia (P < 0.01) on quantitative sensory testing, and pretreatment reported dynamic mechanical allodynia (P < 0.02) all predicted positive response to initial sympathetic block. While sympathetic blocks can be helpful in the reduction of mechanical allodynia, and thus the facilitation of physical and occupational therapy, ultimate response to a regime that includes medications is not predicted by sympathetic block alone.

Preoperative stellate ganglion blockade prevents tourniquet-induced hypertension during general anesthesia

BACKGROUND

Prolonged and excessive inflation of pneumatic tourniquets leads to a hyperdynamic circulatory response. Sympathomimetic activity is an important factor in tourniquet-induced hypertension. Stellate ganglion block specifically blunts sympathetic efferent nerves and prevents hypertension induced by sympathomimetic stimulation. The present study was performed to investigate the effects of stellate ganglion block (SGB) on arterial pressure and heart rate during prolonged tourniquet use under general anesthesia.

METHODS

Twenty patients scheduled for knee arthroscopy were either treated with 10 ml of 1% lidocaine for SGB (SGB group; n = 10), or intramuscular injection (IM group; n = 10) before tourniquet inflation. Comparisons of systolic and diastolic arterial pressure and heart rate were made before and after the induction of anesthesia, 10 min after the lidocaine treatment, every 5 min during the first 60 min after tourniquet inflation, and immediately before and 5 min following deflation. The maximum values of the circulatory variables were compared.

RESULTS

Tourniquet inflation caused increases in the circulatory variables in both groups. Systolic arterial pressure in the SGB group was significantly lower than that in the IM group after 55 min of tourniquet inflation. Diastolic arterial pressure also was significantly lower in the SGB group immediately before the deflation. The maximum values of the three hemodynamic variables were significantly lower in the SGB group. Arterial pressure significantly decreased after tourniquet deflation in the IM group.

CONCLUSION

Ipsilateral SGB attenuated the hyperdynamic response mediated by prolonged tourniquet inflation during knee arthroscopy.

Complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a heterogeneous disorder that falls in the spectrum of neuropathic pain disorders. It is maintained by abnormalities throughout the neuraxis (the peripheral, autonomic, and central nervous systems). The pathophysiology of CRPS is not fully known. There are no scientifically well-established treatments. The diagnostic criteria for CRPS at this time are purely clinical, and the use of diagnostic tests has not been demonstrated. The most appropriate management of CRPS uses a multidisciplinary approach, with the inclusion of medical and psychologic intervention, and physical and occupational therapy. The key is gradual, persistent, functional improvement. The rational use of pain therapies must be grounded in a thorough knowledge of the neurobiology of pain, its endogenous modulation, and the clinical presentation. Potential peripheral pathophysiologic targets (and possible treatments) include increased spontaneous firing and responsiveness of peripheral afferent fibers mediated by inflammatory and other algogenic substances (somatosensory blocks, corticosteroids), altered levels of expression and functioning of multiple ion channels (local anesthetics, calcium channel blockers, anticonvulsants), abnormal interneuronal communication, and increased peripheral expression of adrenergic receptors and sympathetic excitation (sympathetic blocks, alpha-adrenergic antagonists, alpha-2 agonists). CRPS is also perpetuated by central mechanisms, with pathophysiologic targets (and possible treatments) including reorientation of dorsal horn terminals (desensitization techniques), functional reduction in inhibitory interneuron activity (tricyclic antidepressants, gabapentin, opioids), central sensitization and increased central excitability (gabapentin, topiramate, spinal cord stimulation, somatosensory blocks), impaired descending nociceptive inhibition (tricyclic antidepressants, opioids), and adaptive changes in the cortical centers underlying the sensory-discriminative and affective-motivational dimensions of pain (psychologic, physical, and occupational therapies). The treatment choices should be aimed at remodulating, normalizing, disrupting, or preventing the progression of abnormalities in pain processing. Sympathetic nerve blocks should be performed at least once to assess if sympathetically maintained pain is present. To the extent that peripheral somatosensory nerve blocks can diminish nociceptive input to the central nervous system, these techniques may help reduce the nociceptive sensitization of spinal neurons. Pain relief, however it is achieved and however temporary it is, is intended to facilitate participation in functional therapies to normalize use and to improve motion, strength, and dexterity. Psychologic therapies, such as biofeedback and cognitive-behavioral techniques targeting pain, stress, and mood disorders, are valuable adjunctive treatments for pain control and can facilitate functional improvement.

Defining the therapeutic role of local anesthetic sympathetic blockade in complex regional pain syndrome: a narrative and systematic review

OBJECTIVE

There is growing controversy on the value of blocking the sympathetic nervous system for the treatment of complex regional pain syndromes (CRPS). The authors sought to evaluate the efficacy of sympathetic blockade with local anesthetic in these syndromes. In addition, they performed a comprehensive review of the pathophysiology and other treatments for CRPS.

DESIGN

Systematic review of the literature was performed. MEDLINE was searched from 1966 through 1999. The authors identified only three randomized controlled trials (RCTs) that evaluated sympathetic blockade with local anesthetic, but because of differences in study design they were unable to pool the study data. The authors therefore included nonrandomized studies and case series.

INTERVENTIONS

Studies were included if local anesthetic sympathetic blockade was used in at least 10 patients. Studies were excluded if continuous infusion techniques, somatic nerve blocks, or combined sympatholytic therapies were evaluated.

OUTCOME MEASURES

Pain relief was classified as full, partial, or absent. The lack of a comparison group in the studies allowed only the calculation of distribution of the response categories, and the sum of the pooled rates does not equal 100%.

RESULTS

Twenty-nine studies were included that evaluated 1,144 patients. Nineteen studies were retrospective, 5 prospective case series, 3 RCTs, and 2 nonrandomized controlled studies. The quality of the publications was generally poor. Twenty-nine percent of patients had full response, 41% had partial response, and 32% had absent response. It was not possible to estimate the duration of pain relief.

CONCLUSIONS

This review raises questions as to the efficacy of local anesthetic sympathetic blockade as treatment of CRPS. Its efficacy is based mainly on case series. Less than one third of patients obtained full pain relief. The absence of control groups in case series leads to an overestimation of the treatment response that can explain the findings.

Nerve blocks in chronic pain therapy--are there any indications left?

Although diagnostic imaging is now highly developed, neural blockade provides another opportunity to test for a source of pain that may frequently leave no signature. Likewise, many neuropathic pains can not be tested by neurodiagnostic methods. This paper makes a case for the continued use of regional anesthesia to assist in the diagnosis and therapy of chronic pain. In particular, the example of autonomic blocks and blocks of the axial spine are emphasized. Nerve blocks require an understanding of the anatomy, physiology, pharmacology, and the ability to interpret critically their results.

Intradermal injection of norepinephrine evokes pain in patients with sympathetically maintained pain

Tissue injuries, with or without involvement of nerves, may lead to ongoing pain and hyperalgesia to external stimuli. In a subset of patients, the pain is maintained by sympathetic efferent activity (SMP). We investigated if the peripheral administration of the alpha-adrenergic agonist, norepinephrine (NE), in physiologically relevant doses resulted in pain in patients with SMP. To establish the dose of intradermal NE required to induce cutaneous vasoconstriction, NE (1 nM-10 microM, 30 microl) was injected under a laser Doppler probe on the volar forearm of seven normal subjects. A decrease in blood flow was evident at a dose of 10 microM. Twelve patients (five male, seven female) diagnosed to have SMP based on the decrease in pain by a local anesthetic sympathetic blockade (70+/-6%) were enrolled in the study. Pain ratings were obtained continuously for 5 min after intradermal injections of saline and NE (0.1-10 microM) into their hyperalgesic zone and the mirror-image contralateral side. Injections were done during the period of pain relief following a local anesthetic sympathetic blockade. Similar injections were made in eight control subjects. On the affected side of the patients, the two highest concentrations of NE (1 and 10 microM) caused significantly more pain than saline (P<0.05, ANOVA). In contrast, there was no significant pain induced by the NE injections in the unaffected side and in control subjects. Six of nine patients tested reported a marked decrease in pain and hyperalgesia following infusion of phentolamine (1 mg/kg over 10 min). Two of the three patients who did not receive pain relief following phentolamine infusion also did not report pain to the NE injections. We conclude that NE injections produce pain in SMP patients at doses that are at the threshold for producing vasoconstriction. These studies support a role for cutaneous adrenoceptors in the mechanisms of sympathetically maintained pain.

The role of sympathetic nerve blocks in herpes zoster and postherpetic neuralgia

The most common complication of herpes zoster in immunocompetent patients is postherpetic neuralgia (PHN). Sympathetic blocks have been traditionally used for patients with herpes zoster and PHN with three different therapeutic goals: pain relief during acute herpes zoster, pain relief during PHN, and prevention of PHN by treating patients with acute zoster. The role of sympathetic blocks in herpes zoster and PHN remains controversial due to methodologic shortcomings in published studies and the limited current understanding of the role of the sympathetic nervous system in mediating pain. Current theories of the pathophysiology of PHN, the role of the sympathetic nervous system in herpes zoster and PHN, and published studies investigating use of sympathetic nerve blocks in herpes zoster and PHN are reviewed.

Experimental tissue acidosis leads to increased pain in complex regional pain syndrome (CRPS)

The aim of this study was to investigate the role of local acidosis in the generation of pain in complex regional pain syndrome (CRPS). We investigated ten patients with CRPS of the upper extremity with a mean duration of the disease of 43 weeks (range 4-280 weeks) and ten control subjects for sensitivity to infusion of fluids with low pH (pH 6.1). Another group of five CRPS patients and three healthy controls was investigated using the same protocol but neutral infusion fluid (pH 7.4). A motorized syringe pump was installed for a constant infusion of synthetic interstitial fluid (SIF, either acidified (pH 6.1) or neutral) into the skin at the back of the hands and, thereafter, into the interosseus I muscle on both sides. A flow rate of 30 ml/h was chosen for intradermal and 7.5 ml/h for intramuscular infusion over a period of 10 min. The magnitude of pain was rated on an electronic visual analogue scale. Patients were requested to give their ratings every 10 s during the whole stimulation period. The ratings were normalized as fractions of individual grand mean values. We found significantly increased pain perception during infusion of acidified SIF on the affected side in CRPS patients. Low pH fluid into the skin was significantly more painful between 4 and 6 min (ipsi 1.27 normalized rating (NR) (0. 19-1.94), contra 0.31 NR (0.03-0.51), P<0.02) and between 8 and 10 min (ipsi 1.38 NR (0.19-1.94), contra 0.08 NR (0-0.27), P<0.03) on the affected side, while analysis over the whole stimulation period just failed to reach statistical significance (ipsi 281 area under the curve (AUC) (187-834), contra 87 AUC (28-293), P=0.059). Low pH infusion into the muscle was significantly more painful on the affected side during the whole infusion time (ipsi 861 AUC (308-1377), contra 190 AUC (96-528), P<0.01). The quality of the deep pain during infusion into the muscle was described by the patients as very similar to the CRPS-related pain. In controls we found no side differences of pain intensity during low pH stimulation. Neutral SIF evoked no pain at all, neither in CRPS patients (ipsi 0 AUC, contra 0 AUC) nor in healthy controls. Our results suggest that hyperalgesia to protons is present in patients with CRPS. Further, we could demonstrate that pain is not only restricted to the skin but is also generated in deep somatic tissue of the affected limb.

Common nerve blocks in chronic pain management

Anesthesiologists have become increasingly involved with the management of chronic pain patients in the operating room, on the surgical floor, and in the outpatient pain facility setting (often interdisciplinary). Based upon the authors' practice of regional anesthesia, the most specific contribution to chronic pain management arguably remains the practice of diagnostic, prognostic, and therapeutic injections of the neuraxis, peripheral nerves, and the autonomic nervous system.

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.

Pain caused by herpes zoster infection

Postherpetic neuralgia (PHN) is a neuropathic pain disorder that occurs most often in the elderly. This painful condition is uniquely suited for clinical research, resulting in an emerging understanding of the pathophysiology of the persistent pain. Until recently, only the tricyclic antidepressants proved effective for PHN. Controlled trials of a wide variety of therapeutic strategies are in progress or have been recently completed.

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.

Prolonged treatment with transdermal fentanyl in neuropathic pain

Forty-eight patients with noncancer neuropathic pain who had participated in a randomized controlled trial with intravenous fentanyl (FENiv) infusions received prolonged transdermal fentanyl (FENtd) in an open prospective study. Pain relief, side effects, tolerance, psychological dependence, mood changes, and quality of life were evaluated. The value of clinical baseline characteristics and the response to FENiv also was evaluated in terms of the outcome with long-term FENtd. Eighteen patients stopped prematurely because of insufficient pain relief, side effects, or both. Among the remaining 30 patients completing the 12-week dose titration protocol, pain relief was substantial in 13 and moderate in five. Quality of life improved (23%, P < 0.01). Psychological dependence or the induction of depression was not observed. In only one patient did tolerance emerge. There was a significant positive correlation between the pain relief obtained with FENiv and that with prolonged FENtd (r = 0.59, P < 0.0001). We conclude that (1) long-term transdermal fentanyl may be effective in noncancer neuropathic pain without clinically significant management problems and (2) A FENiv-test may assist in selecting neuropathic pain patients who might benefit from prolonged treatment with FENtd.

Analysis of peak magnitude and duration of analgesia produced by local anesthetics injected into sympathetic ganglia of complex regional pain syndrome patients

OBJECTIVE

Pain-relieving effects of lidocaine/bupivicaine local anesthetic (LA) and saline (S) block of sympathetic ganglia (stellate block, 4 patients; lumbar sympathetic block, 3 patients) were compared in 7 complex regional pain syndrome (CRPS) patients on a double-blind crossover basis to evaluate the diagnostic and therapeutic value of local anesthetic sympathetic blocks.

DESIGN

Patients rated their pain on a visual analog scale before and after blocks and were tested for mechanical allodynia one-half hour after blocks. Thereafter, they rated their pain intensity in diaries four times a day for 7 days. Each patient received two blocks, S and LA, and served as his own control.

RESULTS

Both S and LA injections of sympathetic ganglia produced large reductions in pain intensity in 6 of 7 patients 30 minutes after block. These large reductions were accompanied by the reversal of mechanical allodynia in both S and LA. The mean difference between initial peak reduction in pain intensity produced by saline (68.7%) and active local anesthetic (74.4%) did not approach statistical significance. In striking contrast, the mean duration of pain relief was reliably longer in the case of LA (3 days, 18 hours) as compared with S ( 19.9 hours), a difference that occurred in all 7 patients. In a larger sample of 41 CRPS patients, signs of sympathetic efferent blockade, including Homer' s syndrome or skin surface temperature change, were not predictive of initial peak magnitude of pain relief from sympathetic blockade but were predictive of duration of pain reduction.

CONCLUSION

The combination of these results provides evidence that duration of pain relief is affected by injection of local anesthetics into sympathetic ganglia. These results indicate that both magnitude and duration of pain reduction should be closely monitored to provide optimal efficacy in procedures that use local anesthetics to treat CRPS.

Randomised double-blind active-placebo-controlled crossover trial of intravenous fentanyl in neuropathic pain

BACKGROUND

The effectiveness of opioid analgesics in non-cancer neuropathic pain is unpredictable and can be disappointing. It is not clear whether opioids, when effective, relieve pain by decreasing pain intensity or pain unpleasantness or by their sedative effect. The aim of this prospective randomised double-blind placebo-controlled crossover trial was to assess relief of pain intensity and pain unpleasantness with intravenous infusions of fentanyl.

METHODS

We compared the analgesic effect of intravenous dose titration of fentanyl with diazepam (active placebo) or saline (inert placebo) in 53 patients with different types of neuropathic pain. Patients were randomly assigned two consecutive infusions: fentanyl plus diazepam (27 patients) or fentanyl plus saline (26 patients). Study medication was infused at a constant rate for a maximum of 5 h. Pain, sedation, and side-effects were assessed from the start of infusion for 8 h. The primary outcome measure was maximum relief of pain intensity.

FINDINGS

One patient in the fentanyl/diazepam group and two in the fentanyl/saline group were withdrawn. Maximum relief of pain intensity was better with fentanyl than with diazepam (66% [95% CI 53-80] vs 23% [12-35]) or with saline (50% [36-63] vs 12% [4-20]). The beneficial effect of fentanyl was independent of the type of neuropathic pain and the degree of sedation. Fentanyl therapy produced equal relief of pain intensity and pain unpleasantness, whereas diazepam and saline did not reduce either pain index. Patients reported significantly more side-effects while receiving fentanyl than during diazepam or saline infusion (p < 0.0001), but none of the side-effects was severe.

INTERPRETATION

Fentanyl may relieve non-cancer neuropathic pain by its intrinsic analgesic effect. The clinical characteristics of neuropathic pain do not predict response to opioids.

Quantitative sensory testing

Quantitative sensory testing has become commonplace in clinical neurophysiology units. Measurement of the thermal and vibratory senses provides an estimate on function of sensory small and large fibers, respectively. Being psychophysical parameters, sensory threshold values are not objective, and various test algorithms have been developed aiming at optimized results. In this review the various test algorithms are screened, and their relative advantages and disadvantages are discussed. Considerations of quality control are reviewed, and the main fields of clinical application are described.

An anatomic study of neuropeptide immunoreactivities in the lumbar dura mater after lumbar sympathectomy

STUDY DESIGN

The distribution and density of nerve innervation in the lumbar dura mater after lumbar sympathectomy were assessed in wistar rats.

OBJECTIVE

To provide basic information on the interaction between sympathetic and sensory nerves in patients with low back pain.

SUMMARY OF BACKGROUND DATA

Many studies have indicated that the sinuvertebral nerve has an important role in innervating the tissues around the vertebrae. However, the origin, innervating pattern, and connections between the nerves are still controversial. It is well known that pain is often accompanied with sympathetic symptoms and exaggerated by sympathetic stimuli. Occasionally, anesthetic block at the L2 or L3 sympathetic ganglion relieves low back pain or symptoms associated with low back pain. The authors assessed the changes of the density and distribution of nerve innervation of the lumbar dura mater after lumbar sympathectomy.

METHODS

Normal adult rats were sympathectomized at L2-L3. The threshold for thermal noxious pain by hot-plate analgesia test and changes in neuropeptides in the lumbar dura mater and dorsal root ganglia using light microscopic immunohistochemistry were assessed and compared with control rats.

RESULTS

In the hot-plate analgesia test, sympathectomized rats increased their hot-plate latency time compared with that of sham-operated rats. Density of calcitonin gene-related peptide immunoreactive fibers in sympathectomy side of the lumbar dura mater decreased to 45.5% compared with the contralateral side. The number and size of calcitonin gene-related peptide immunoreactive cells in dorsal root ganglia showed no difference between sympathectomized and contralateral side.

CONCLUSION

Sympathectomy increased the pain threshold and made the sympathectomized rats hypesthetic. A large numbers of sensory fibers innervated the lumbar dura mater via L2-L3 sympathetic nerve in rats. Sympathectomy reduced the number of these nerve fibers in the lumbar dura mater. Sympathetic nerves may play an important role for low back pain involving the lumbar dura mater.