Pain

Published by Elsevier
Online ISSN: 1872-6623
Print ISSN: 0304-3959
Publications
The analgesic and adverse effects of intrathecal methadone 5 mg, 10 mg and 20 mg were assessed and compared with intrathecal morphine 0.5 mg. The study was conducted on 38 patients who underwent total knee or hip replacement surgery. The intrathecal opioid was administered at the end of surgery and assessments began 1 h thereafter and continued for 24 h. Pain measurements, supplementary analgesia requirements, and adverse effects were recorded. Intrathecal morphine 0.5 mg provided effective and prolonged analgesia. Intrathecal methadone 5 mg, 10 mg, and 20 mg produced good analgesia of 4 h duration. Thereafter the median pain scores with intrathecal methadone were consistently higher (worse) than those with intrathecal morphine (P less than 0.05). The time to the onset of discomfort severe enough to require supplemental morphine was longer after intrathecal morphine than following methadone (15 h with morphine 0.5 mg; 6.25 h, 6.5 h and 6 h with methadone 5 mg, 10 mg, and 20 mg respectively: P less than 0.05). Central nervous system depression manifesting as respiratory depression, hypotension, and excessive drowsiness occurred in 3 of 8 patients injected with methadone 20 mg intrathecally. Generalized pruritus, nausea, vomiting, and urinary retention were common and equally distributed among the treatment groups. We conclude that both intrathecal morphine 0.5 mg and methadone 5, 10, and 20 mg provide excellent analgesia but that morphine has a more prolonged effect. Methadone 20 mg produced unacceptable side effects. Clinical evidence for rostral spread of methadone within the CSF, as indicated by facial itching and excessive drowsiness, was less apparent with 5 mg than with 10 and 20 mg. Various explanations for the observed differences between the drugs are discussed.
 
Neuropathic pain conditions are common after nerve injuries and are suggested to be regulated in part by genetic factors. We have previously demonstrated a strong genetic influence of the rat major histocompatibility complex on development of neuropathic pain behavior after peripheral nerve injury. In order to study if the corresponding human leukocyte antigen complex (HLA) also influences susceptibility to pain, we performed an association study in patients that had undergone surgery for inguinal hernia (n=189). One group had developed a chronic pain state following the surgical procedure, while the control group had undergone the same type of operation, without any persistent pain. HLA DRB1genotyping revealed a significantly increased proportion of patients in the pain group carrying DRB1(∗)04 compared to patients in the pain-free group. Additional typing of the DQB1 gene further strengthened the association; carriers of the DQB1(∗)03:02 allele together with DRB1(∗)04 displayed an increased risk of postsurgery pain with an odds risk of 3.16 (1.61-6.22) compared to noncarriers. This finding was subsequently replicated in the clinical material of patients with lumbar disc herniation (n=258), where carriers of the DQB1(∗)03:02 allele displayed a slower recovery and increased pain. In conclusion, we here for the first time demonstrate that there is an HLA-dependent risk of developing pain after surgery or lumbar disc herniation; mediated by the DRB1(∗)04 - DQB1(∗)03:02 haplotype. Further experimental and clinical studies are needed to fine-map the HLA effect and to address underlying mechanisms.
 
The effect of PF-04457845, a potent and selective fatty acid amide hydrolase-1 (FAAH1) inhibitor, on pain due to osteoarthritis of the knee was investigated in a randomised placebo and active-controlled clinical trial. The trial involved 2 periods (separated by a 2-week washout) consisting of a 1-week wash-in phase followed by 2weeks double-blind treatment. Patients received single-blind placebo throughout the wash-in and washout periods. Patients were randomised to receive either 4mg q.d. PF-04457845 followed by placebo (or vice versa), or 500mg b.i.d. naproxen followed by placebo (or vice versa). The primary end point was the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain score. The trial had predefined decision rules based on likelihood that PF-04457845 was better or worse than the standard of care (considered to be a 1.8 reduction in WOMAC pain score compared to placebo). A total of 74 patients were randomised to 1 of 4 treatment sequences. The mean differences (80% confidence intervals) from placebo in WOMAC pain score were 0.04 (-0.63 to 0.71) for PF-04457845 and -1.13 (-1.79 to -0.47) for naproxen, indicating that whilst naproxen seemed efficacious, PF-04457845 was not differentiated from placebo. The study was stopped at the interim analysis for futility. PF-04457845 decreased FAAH activity by >96% and substantially increased 4 endogenous substrates (fatty acid amides). PF-04457845 was well tolerated in osteoarthritis patients, and there was no evidence of cannabinoid-type adverse events. The lack of analgesic effect of FAAH1 inhibition in humans is in contrast to data from animal models. This apparent disconnect between species needs further study.
 
The TRPV1 antagonist A-995662 demonstrates analgesic efficacy in monoiodoacetate-induced osteoarthritic (OA) pain in rat, and repeated dosing results in increased in vivo potency and a prolonged duration of action. To identify possible mechanism(s) underlying these observations, release of neuropeptides and the neurotransmitter glutamate from isolated spinal cord was measured. In OA rats, basal release of glutamate, bradykinin and calcitonin gene-related peptide (CGRP) was significantly elevated compared to naïve levels, whereas substance P (SP) levels were not changed. In vitro studies showed that capsaicin-evoked TRPV1-dependent CGRP release was 54.7+/-7.7% higher in OA, relative to levels measured for naïve rats, suggesting that TRPV1 activity was higher under OA conditions. The efficacy of A-995662 in OA corresponded with its ability to inhibit glutamate and CGRP release from the spinal cord. A single, fully efficacious dose of A-995662, 100 micromol/kg, reduced spinal glutamate and CGRP release, while a single sub-efficacious dose of A-995662 (25 micromol/kg) was ineffective. Multiple dosing with A-995662 increased the potency and duration of efficacy in OA rats. Changes in efficacy did not correlate with plasma concentrations of A-995662, but were accompanied with reductions in spinal glutamate release. These findings suggest that repeated dosing of TRPV1 antagonists enhances therapeutic potency and duration of action against OA pain, at least in part, by the sustained reduction in release of glutamate and CGRP from the spinal cord.
 
Therapeutic use of general sodium channel blockers, such as lidocaine, can substantially reduce the enhanced activity in sensory neurons that accompanies chronic pain after nerve or tissue injury. However, because these general blockers have significant side effects, there is great interest in developing inhibitors that specifically target subtypes of sodium channels. Moreover, some idiopathic small-fiber neuropathies are driven by gain-of-function mutations in specific sodium channel subtypes. In the current study we focus on one subtype, the voltage-gated sodium channel 1.8 (Nav1.8). Nav1.8 is preferentially expressed in nociceptors and gain-of-function mutations in Nav1.8 result in painful mechanical hypersensitivity in humans. Here, we used the recently developed gain-of-function Nav1.8 transgenic mouse strain, Possum, to investigate Nav1.8-mediated peripheral afferent hyperexcitability. This gain-of-function mutation resulted in increased mechanically-evoked action potential firing in subclasses of Aβ, Aδ and C-fibers. Moreover, mechanical stimuli initiated bursts of action potential firing in specific subpopulations that continued for minutes after removal of the force and were not susceptible to conduction failure. Surprisingly, despite the intense afferent firing, the behavioral effects of the Nav1.8 mutation were quite modest as only frankly noxious stimuli elicited enhanced pain behavior. These data demonstrate that a Nav1.8 gain-of-function point mutation contributes to intense hyperexcitability along the afferent axon within distinct sensory neuron subtypes.
 
Antisense (AS) oligodeoxynucleotides (ODNs) targeting the Nav 1.8 sodium channel have been reported to decrease inflammatory hyperalgesia and L5/L6 spinal nerve ligation-induced mechanical allodynia in rats. The present studies were conducted to further characterize Nav 1.8 AS antinociceptive profile in rats to better understand the role of Nav 1.8 in different pain states. Consistent with earlier reports, chronic intrathecal Nav 1.8 AS, but not mismatch (MM), ODN decreased TTX-resistant sodium current density (by 60.5+/-10.2% relative to MM; p<0.05) in neurons from L4 to L5 dorsal root ganglia and significantly attenuated mechanical allodynia following intraplantar complete Freund's adjuvant. In addition, 10 days following chronic constriction injury of the sciatic nerve, Nav 1.8 AS, but not MM, ODN also attenuated mechanical allodynia (54.3+/-8.2% effect, p<0.05 vs. MM) 2 days after initiation of ODN treatment. The anti-allodynic effects remained for the duration of the AS treatment, and CCI rats returned to an allodynic state 4 days after discontinuing AS. In contrast, Nav 1.8 AS ODN failed to reduce mechanical allodynia in the vincristine chemotherapy-induced neuropathic pain model or a skin-incision model of post-operative pain. Finally, Nav 1.8 AS, but not MM, ODN treatment produced a small but significant attenuation of acute noxious mechanical sensitivity in naïve animals (17.6+/-6.2% effect, p<0.05 vs. MM). These data demonstrate a greater involvement of Nav 1.8 in frank nerve injury and inflammatory pain as compared to acute, post-operative or chemotherapy-induced neuropathic pain states.
 
We investigated adverse events (AEs) associated with perioperative tenoxicam in a double-blind, prospective, randomised study. Patients undergoing surgery, screened for contraindications to non-steroidal anti-inflammatory drug, received tenoxicam (n=750) on 2843 days or placebo (n=251) on 988 days, in courses of 1-12 days. There was no increase in the overall incidence of side effects with tenoxicam (33 vs 38% with placebo: P=0.15), or in major side effects (3.9 vs 2.0% with placebo: P=0.11). Of major side effects possibly or probably related to tenoxicam (2.1 vs 1.2% with placebo: P=0.26), all but one involved post-operative surgical site bleeding. However, in the subgroup of patients undergoing otorhinolaryngology surgery, surgical site bleeding occurred in 18 of 171 (10.5%) patients on tenoxicam and one of 57 (1.8%) on placebo (P=0.026); of these, nine in the tenoxicam group and 0 in the placebo were classified as major (P=0.07). One patient on tenoxicam experienced endoscopically proven duodenal ulceration with malaena. In conclusion, perioperative tenoxicam is well tolerated in comparison with placebo and the incidence of drug-related major AEs (other than post-operative bleeding) is no greater than 1 in 150 in low risk patients, but in patients undergoing otorhinolaryngological surgery there may be an increased risk of post-operative bleeding.
 
Dose-response studies for (A) paracetamol (i.v.) and (B) venlafaxine (s.c.) in the formalin test. The results are expressed as meanGSEM of the cumulative biting and licking time during each phase (nZ8). Data were analysed using one-way ANOVA, followed by a Student-Newman-Keuls' test. *P! 0.05 vs. control group. VEH, saline containing 0.02 g/mL trisodic citrate; PARA, paracetamol; VLX, venlenfaxine.
Dose-response studies for (A) paracetamol (i.v.) and (B) venlafaxine (s.c.) in the paw pressure test. Data are presented as meanGSEM of differences between post-and pre-drug values (Dg) (nZ8). *P!0.05 vs. pre-drug values using two-way ANOVA, followed by a Dunnett's test. AUCs were calculated by summing the difference scores obtained at each individual time using the trapezoidal method. *P!0.05 vs. control group using one-way ANOVA followed by a Student-Newman-Keuls' test. VEH, saline containing 0.02 g/mL trisodic citrate; PARA, paracetamol; VLX, venlenfaxine.
The regulation of nociceptive processing by 5-HT at the spinal level is intricate since the neurotransmitter has been implicated in both pro and antinociception. The aim of our study was to investigate, according to the nature of the noxious stimulus, how the blockade of spinal 5-HT(1A) receptors could influence the antinociceptive actions of exogenous 5-HT as well as two analgesics involving endogenous 5-HT, paracetamol and venlafaxine. Rats were submitted either to the formalin test (tonic pain) or the paw pressure test (acute pain). WAY-100635 (40 microg/rat, i.t.), a selective 5-HT(1A) receptor antagonist, had no intrinsic action in either test. However, in the formalin test, it blocked the antinociceptive action of 5-HT (50 microg/rat, i.t.) and paracetamol (300 mg/kg, i.v.) in both phases of biting/licking behaviour and that of venlafaxine (2.5 mg/kg, s.c.) in the late phase only. In the paw pressure test, the combination of sub-effective doses of 5-HT (0.01 microg/rat, i.t.), paracetamol (50 mg/kg, i.v.) or venlafaxine (20 mg/kg, s.c.) with WAY-100635 led to a significant antinociceptive effect, which seems to depend on the reinforcement of the activity of inhibitory GABAergic interneurones. In conclusion, both direct stimulation of the spinal 5-HT(1A) receptors by 5-HT, and indirect stimulation using paracetamol or venlafaxine can differently influence pain transmission. We propose that the nature of the applied nociceptive stimulus would be responsible for the dual effect of the 5-HT(1A) receptors rather than the hyperalgesic state or the supraspinal integration of the pain message.
 
The capsaicin receptor (TRPV1) antagonist ABT-102 demonstrates efficacy in multiple preclinical pain models. However, evolving clinical data for this compound class suggest potentially profound drug-induced thermosensory impairment. Safety and tolerability of ABT-102 were assessed in a multiple-dose, double-blind, placebo-controlled, randomized healthy volunteer trial. Thirty-six participants were randomized in a 2:1 ratio to ABT-102:placebo in 3 dose groups (1 mg, 2 mg, and 4 mg twice a day) and confined to an inpatient research unit for a 7-day treatment period and 3 follow-up days. Outcome measures included: oral and cutaneous cold detection, warm detection (WDT), and heat pain thresholds (HPT); oral perceived heat intensity (oral liquid test); time to hand withdrawal (water bath test); and cutaneous pain intensity (long thermal stimulus). Significant dose-dependent (placebo- and baseline-adjusted) increases in HPT and reduced painfulness of suprathreshold heat were present from days 1-7. For ABT-102 4 mg twice a day, model-based mean differences from placebo (95% confidence interval) were as follows: oral HPT, day 1=2.5°C (0.6-4.4), day 5=4.4°C (2.5-6.3); cutaneous HPT, day 2=3.3°C (1.4-5.3), day 5=5.3°C (3.3-7.2); oral WDT, day 1=2.6°C (0.5-4.7), day 5=2.7°C (0.6-4.9); cutaneous WDT, day 2=1.3 (0.0-2.6), day 5=1.6 (0.3-2.8) (all P<0.05). Oral liquid test and water bath test results followed a similar pattern. There was no effect on cutaneous cold detection. All effects were fully reversed by day 10. There were no other relevant safety findings. Core body temperature remained below 39°C in all participants. In conclusion, ABT-102 potently and reversibly increased HPT and reduced painfulness of suprathreshold oral/cutaneous heat.
 
Transient receptor potential vanilloid type 1 (TRPV1) is a ligand-gated ion channel that functions as an integrator of multiple pain stimuli including heat, acid, capsaicin and a variety of putative endogenous lipid ligands. TRPV1 antagonists have been shown to decrease inflammatory pain in animal models and to produce limited hyperthermia at analgesic doses. Here, we report that ABT-102, which is a potent and selective TRPV1 antagonist, is effective in blocking nociception in rodent models of inflammatory, post-operative, osteoarthritic, and bone cancer pain. ABT-102 decreased both spontaneous pain behaviors and those evoked by thermal and mechanical stimuli in these models. Moreover, we have found that repeated administration of ABT-102 for 5-12 days increased its analgesic activity in models of post-operative, osteoarthritic, and bone cancer pain without an associated accumulation of ABT-102 concentration in plasma or brain. Similar effects were also observed with a structurally distinct TRPV1 antagonist, A-993610. Although a single dose of ABT-102 produced a self-limiting increase in core body temperature that remained in the normal range, the hyperthermic effects of ABT-102 effectively tolerated following twice-daily dosing for 2 days. Therefore, the present data demonstrate that, following repeated administration, the analgesic activity of TRPV1 receptor antagonists is enhanced, while the associated hyperthermic effects are attenuated. The analgesic efficacy of ABT-102 supports its advancement into clinical studies.
 
NW-1029, a benzylamino propanamide derivative, was selected among several molecules of this chemical class on the basis of its affinity for the [(3)H]batracotoxin ligand displacement of the Na(+) channel complex and also on the basis of its voltage and use-dependent inhibitory action on the Na(+) currents of the rat DRG (dorsal root ganglia) sensory neuron. This study evaluated the analgesic activity of NW-1029 in animal models of inflammatory and neuropathic pain (formalin test in mice, complete Freund's adjuvant and chronic constriction injury in rats) as well as in acute pain test (hot-plate and tail-flick in rats). Orally administered NW-1029 dose-dependently reduced cumulative licking time in the early and late phase of the formalin test (ED(50)=10.1 mg/kg in the late phase). In the CFA model, NW-1029 reversed mechanical allodynia (von Frey test) after both i.p. and p.o. administration (ED(50)=0.57 and 0.53 mg/kg), respectively. Similarly, NW-1029 reversed mechanical allodynia in the CCI model after both i.p. and p.o. administration yielding an ED(50) of 0.89 and 0.67 mg/kg, respectively. No effects were observed in the hot-plate and tail-flick tests up to 30 mg/kg p.o. The compound orally administered (0.1-10 mg/kg) was well tolerated, without signs of neurological impairment up to high doses (ED(50)=470 and 245 mg/kg in rat and mice Rotarod test, respectively). These results indicate that NW-1029 has anti-nociceptive properties in models of inflammatory and neuropathic pain.
 
Sensitivity analysis: percent change in total cost to a 10% change in the cost or volume of each component.  
This paper reports the results of a 'cost-of-illness' study of the socio-economic costs of back pain in the UK. It estimates the direct health care cost of back pain in 1998 to be pound1632 million. Approximately 35% of this cost relates to services provided in the private sector and thus is most likely paid for directly by patients and their families. With respect to the distribution of cost across different providers, 37% relates to care provided by physiotherapists and allied specialists, 31% is incurred in the hospital sector, 14% relates to primary care, 7% to medication, 6% to community care and 5% to radiology and imaging used for investigation purposes. However, the direct cost of back pain is insignificant compared to the cost of informal care and the production losses related to it, which total pound10668 million. Overall, back pain is one of the most costly conditions for which an economic analysis has been carried out in the UK and this is in line with findings in other countries. Further research is needed to establish the cost-effectiveness of alternative back pain treatments, so as to minimise cost and maximise the health benefit from the resources used in this area.
 
Chemokine signaling is important in neuropathic pain, with microglial cells expressing CCR2 playing a well-established key role. DAPTA, a HIV gp120-derived CCR5 entry inhibitor, has been shown to inhibit CCR5-mediated monocyte migration and to attenuate neuroinflammation. We report here that as a stabilized analog of DAPTA, the short peptide RAP-103 exhibits potent antagonism for both CCR2 (half maximal inhibitory concentration [IC50] 4.2 pM) and CCR5 (IC50 0.18 pM) in monocyte chemotaxis. Oral administration of RAP-103 (0.05-1 mg/kg) for 7 days fully prevents mechanical allodynia and inhibits the development of thermal hyperalgesia after partial ligation of the sciatic nerve in rats. Administered from days 8 to 12, RAP-103 (0.2-1 mg/kg) reverses already established hypersensitivity. RAP-103 relieves behavioral hypersensitivity, probably through either or both CCR2 and CCR5 blockade, because by using genetically deficient animals, we demonstrated that in addition to CCR2, CCR5 is also required for the development of neuropathic pain. Moreover, RAP-103 is able to reduce spinal microglial activation and monocyte infiltration, and to inhibit inflammatory responses evoked by peripheral nerve injury that cause chronic pain. Our findings suggest that targeting CCR2/CCR5 should provide greater efficacy than targeting CCR2 or CCR5 alone, and that dual CCR2/CCR5 antagonist RAP-103 has the potential for broad clinical use in neuropathic pain treatment.
 
Neuronal nicotinic receptor (NNR) agonists such as ABT 594 have been shown to be effective in a wide range of preclinical models of acute and neuropathic pain. The present study, using the NNR agonist A-85380, sought to determine if NNR agonists are acting via similar or differing mechanisms to induce anti-nociception and anti-allodynia. A systemic administration of the quaternary NNR antagonist chlorisondamine (0.4 micromol/kg, intraperitoneal (i.p.)) did not alter A-85380-induced (0.75 micromol/kg, i.p.) anti-nociception in the rat paw withdrawal model of acute thermal pain. In contrast, previous studies have demonstrated that blockade of central NNRs by prior administration of chlorisondamine (10 microg i.c.v.) prevents A-85380 induced anti-nociception indicating a predominantly central site of action of NNR agonists in relieving acute pain. In the rat spinal nerve ligation model of neuropathic pain, A-85380 induced a dose-dependent anti-allodynia (0.5-1.0 micromol/kg) that was blocked by pretreatment with mecamylamine (1 micromol/kg). Interestingly, unlike acute pain, both systemic and central administration of chlorisondamine blocked A-85380-induced anti-allodynia, an effect that was determined not to be due to a non-specific effect of chlorisondamine or to chlorisondamine crossing the blood-brain barrier. The peripheral site of action was shown not to be the primary receptive field, since A-85380 had equally potent anti-allodynic effects when it was injected into either the affected or unaffected paw. In contrast, infusion of A-85380 directly onto the L5 dorsal root ganglion on the affected side resulted in a dose-dependent and marked anti-allodynia (10-20 microg) at doses that had no effect when injected systemically. This effect was blocked by pretreatment with chlorisondamine. Together these data further support the idea that different mechanisms underlie different pain states and suggest that the effects of NNR agonists in neuropathic pain may be due in part to peripheral actions of the compounds.
 
The effects of tizanidine, a new muscle relaxant, 5-chloro-4-(2-imidazolin-2-yl-amino)-2,1,3-benzothiazole (DS 103-282) were studied on the activity of lumbar dorsal horn convergent neurons in anaesthetized paralysed rats. Following i.v. administration of tizanidine both the A- and C-fibre evoked responses were depressed in a dose-dependent manner in the 0.125-1.0 mg/kg range. The smaller dose employed (0.125 mg/kg) induced a significant depression of the C-fibre evoked responses (39.6 +/- 13.4% of the control responses) and a total recovery was observed 10 min after the injection: when the doses were increased, stronger and longer-lasting depressant effects were obtained. Identical but less powerful effects were observed on A-fibre responses. None of the depressive effects was correlated with variations in blood pressure. Microelectrophoretically applied tizanidine was found to depress current-dependently, the discharges of convergent neurones evoked by microelectrophoretically applied DL-homocysteic acid. In contrast, tizanidine (0.5, 1 mg/kg; i.v.) was found to be ineffective against the activities of non-nociceptive neurones triggered by mechanical stimulation of their receptive fields. It is concluded that tizanidine depresses specifically the activities of dorsal horn convergent neurones, probably in part by a post-synaptic inhibitory action. Owing to the role of convergent neurones in pain processes, the present result could explain, at least partially, the analgesic action of this compound.
 
Chronic pain after surgery is recognised as an important post-operative complication; recent studies have shown up to 30% of patients reporting persistent pain following mastectomy and inguinal hernia repair. No large-scale studies have investigated the epidemiology of chronic pain at two operative sites following coronary artery bypass grafting (CABG). This paper reports the follow-up of a cohort of 1348 patients who underwent cardiac surgery between 1996 and 2000 at one cardiothoracic unit in northeast Scotland. Chronic pain was defined as pain in the location of surgery, different from that suffered pre-operatively, arising post-operatively and persisting beyond 3 months. The survey questionnaire consisted of the short-form-36 (SF-36), Rose angina questionnaire, McGill pain questionnaire and the University of California and San Francisco (UCSF) pain service questionnaire. Of the 1080 responders, 130 reported chronic chest pain, 100 chronic post-saphenectomy pain and 194 reported pain at both surgical sites. The cumulative prevalence of post-cardiac surgery pain was 39.3% (CI(95) 36.4-42.2%) and mean time of 28 months since surgery (SD 15.3 months). Patients who reported pain at both sites had lower quality of life scores across all eight health domains compared to patients with pain at one site only and those who were pain-free. Prevalence of chronic pain decreased with age, from 55% in those aged under 60 years to 34% in patients over 70 years. Patients with pre-operative angina and those who were overweight or obese (BMI>/=25) at the time of surgery were more likely to report chronic pain. Chronic pain following median sternotomy and saphenous vein harvesting is more common than hitherto reported and that patients undergoing CABG should be warned of this possibility.
 
We present a systematic review of prospective cohort studies. Our aim was to assess prognostic factors associated with functional recovery of patients with whiplash injuries. The failure of some patients to recover following whiplash injury has been linked to a number of prognostic factors. However, there is some inconsistency in the literature and there have been no systematic attempts to analyze the level of evidence for prognostic factors in whiplash recovery. Studies were selected for inclusion following a comprehensive search of MEDLINE, EMBASE, CINAHL, the database of the Dutch Institute of Allied Health Professions up until April 2002 and hand searches of the reference lists of retrieved articles. Studies were selected if the objective was to assess prognostic factors associated with recovery; the design was a prospective cohort study; the study population included at least an identifiable subgroup of patients suffering from a whiplash injury; and the paper was a full report published in English, German, French or Dutch. The methodological quality was independently assessed by two reviewers. A study was considered to be of 'high quality' if it satisfied at least 50% of the maximum available quality score. Two independent reviewers extracted data and the association between prognostic factors and functional recovery was calculated in terms of risk estimates. Fifty papers reporting on twenty-nine cohorts were included in the review. Twelve cohorts were considered to be of 'high quality'. Because of the heterogeneity of patient selection, type of prognostic factors and outcome measures, no statistical pooling was able to be performed. Strong evidence was found for high initial pain intensity being an adverse prognostic factor. There was strong evidence that for older age, female gender, high acute psychological response, angular deformity of the neck, rear-end collision, and compensation not being associated with an adverse prognosis. Several physical (e.g. restricted range of motion, high number of complaints), psychosocial (previous psychological problems), neuropsychosocial factors (nervousness), crash related (e.g. accident on highway) and treatment related factors (need to resume physiotherapy) showed limited prognostic value for functional recovery. High initial pain intensity is an important predictor for delayed functional recovery for patients with whiplash injury. Often mentioned factors like age, gender and compensation do not seem to be of prognostic value. Scientific information about prognostic factors can guide physicians or other care providers to direct treatment and to probably prevent chronicity.
 
Previous to October 1st, 1981, 8 major Danish anaesthesiological departments registered 105 patients treated with extradural opiates for a period of more than 7 days, partially or completely on outpatient basis. Ninety-four suffered from painful malignant diseases and 11 patients from various painful benign diseases. The mean period of treatment was 65 days (range: 7-283 days) and of these 49 days (2-266 days) as outpatients. The total number of inserted epidural catheters was 215, equivalent of an average of 2 per patient (range 1-5). Reasons for removing an extradural catheter were injection-related pain, difficulty in injecting the desired volume, and displacement of catheter. Morphine chloride, in a solution of 0.4 mg/ml of normal saline, was the main choice as analgesic agent (90 patients). The mean daily dose of this drug totalled 12.6 +/- 4.8 mg (S.D.) (range: 4-30 mg) distributed as 2.7 +/- 0.9 (S.D.) (range: 1-6) daily injections. Twelve patients were treated with buprenorphine extradurally. Satisfactory pain relief was achieved for 70 patients (67%) who managed with extradural opiates as sole analgesic treatment. One patient developed septicaemia with a non-fatal outcome probably originating from some other focus. Apart from this no serious side effects were reported. Medically unskilled persons or relatives were responsible for instillation of all extradural opiates with 42 patients and partially responsible with 14 patients. Eleven patients managed injections without assistance. District nurses took care of medication for 46 patients, aided by a general practitioner in 5 cases. Three patients were supplied with continuous extradural infusion by means of a Mill Hill microinfusion pump.
 
The unpleasantness of itching is reduced by cooling. Although previous research suggests the presence of a central itch modulation system, there is little documentation about the modulation system in the brain. In the present study, we investigated the modulating system of the itching sensation in human brains using positron emission tomography and H(2) (15)O. The significant increases of regional cerebral blood flow caused by histamine stimuli using iontophoresis were observed in the anterior cingulate cortex (BA24), the thalamus, the parietal cortex (BA40 and BA7), the dorsolateral prefrontal cortex (BA46) and the premotor cortex (BA6). We did not observe any changes in the secondary somatosensory cortex (S2) during the itching stimulus, corresponding to the previous imaging studies concerning itching. Activation in these areas related to itching stimuli was decreased by a simultaneous stimulation of itching and cold pain (the dual stimuli), as compared to itching alone. Interestingly, the midbrain, including periaqueductal gray matter (PAG), was only activated during the dual stimuli. PAG is well known to be a modulating noxious stimulus. Here we hypothesize that the activation of PAG may also be related to the itch modulation. These findings indicate that the modified brain activities in the PAG, the cingulate, the frontal and the parietal cortex might be associated with the itch modulation in the central nervous system and that the S2 might not be primarily involved in processing the itching perception in the brain since the activity of S2 was not observed in any concentration of itching stimuli.
 
Spinal application of opiates is the cornerstone of potent analgesia. In the present study, opiate analgesia was investigated after cutaneous application of a recombinant herpes simplex virus type-1 (HSV-1) encoding micro-opioid receptor (microOR) cDNA in reverse orientation with respect to the human cytomegalovirus early enhancer-promoter. Hind paw application of this recombinant vector was used in order to attenuate expression of the microOR in primary afferents and determine whether recombinant vector application would differentially affect the antinociceptive effects of the specific microOR agonist, [D-Ala(2),N-MePhe(4),Gly-ol(5)] enkephalin (DAMGO), on behavioral responses mediated by C- and Adelta-thermonociceptors. The recombinant vector encoding the Escherichia coli lacZ gene marker, KHZ, served as a control virus. Dorsal hind paw surfaces of female Swiss-Webster mice were treated with one of these two viruses (1x10(8)pfu, 10 microl) or vehicle (uninfected). Immunohistochemistry and quantitative image analyses revealed decreased microOR expression in the superficial dorsal horns ipsilateral to hind paws treated with AMOR, but not KHZ. To add, behavioral foot withdrawal latencies of AMOR- and KHZ-treated hind paws demonstrated dose-dependent antinociception after intrathecal DAMGO administration. However, cutaneous application of dorsal hind paw surfaces treated with AMOR, but not KHZ, caused a rightward shift in the C-fiber dose-response, thus, indicating a loss of potency of intrathecal DAMGO. Loss or diminution of DAMGO potency during Adelta-fiber-mediated responses was not observed. These immunohistochemistry and behavioral results of novel, recombinant HSV-1 vector microOR 'knock-down' in nociceptor afferent fibers provide additional evidence for presynaptic localization of microORs on central C-, but not Adelta-terminals.
 
Although pain assessment is a vital preliminary step towards the satisfactory control of cancer pain, data on the prevalence of different pain syndromes are rare. In a prospective study of 2266 cancer patients, we assessed localisations, aetiologies and pathophysiological mechanisms of the pain syndromes. Thirty percent of the patients presented with 1, 39% with 2 and 31% with 3 or more distinct pain syndromes. The majority of patients had pain caused by cancer (85%) or antineoplastic treatment (17%); 9% had pain related to cancer disease and 9% due to aetiologies unrelated to cancer. Pain could be classified as originating from nociceptors in bone (35%), soft tissue (45%) or visceral structures (33%) or otherwise as of an neuropathic origin (34%). In most patients, pain syndromes were located in the lower back (36%), abdominal region (27%), thoracic region (23%), lower limbs (21%), head (17%) and pelvic region (15%). The main pain syndrome was also coded according to the IASP Classification of Chronic Pain. Regions and systems affected by the main pain syndrome showed large variation depending on the site of cancer origin, whereas temporal characteristics, intensity and aetiology were not markedly influenced by the cancer site. The variety of pain syndromes evaluated in our patients confirms the importance of comprehensive pain assessment prior to treatment.
 
This systematic review summarizes the results of 10 years of laboratory research on pain and sex/gender. An electronic search strategy was designed by a medical librarian to access multiple databases. A total of 172 articles published between 1998 and 2008 were retrieved, analyzed, and synthesized. The second set of results presented in this review (129 articles) examined various biopsychosocial factors that may contribute to differences in pain sensitivity between healthy women and men. The results revealed that the involvement of hormonal and physiological factors is either inconsistent or absent. Some studies suggest that temporal summation, allodynia, and secondary hyperalgesia may be more pronounced in women than in men. The evidence to support less efficient endogenous pain inhibitory systems in women is mixed and does not necessarily apply to all pain modalities. With regard to psychological factors, depression may not mediate sex differences in pain perception, while the role of anxiety is ambiguous. Cognitive and social factors appear to partly explain some sex-related differences. Finally, past individual history may be influential in female pain responses. However, these conclusions must be treated with much circumspection for various methodological reasons. Furthermore, some factors/mechanisms remain understudied in the field. There is also a need to assess and improve the ecological validity of findings from laboratory studies on healthy subjects, and perhaps a change of paradigm needs to be considered at this point in time to better understand the factors that influence the experience of women and men who suffer from acute or chronic pain.
 
Medication-overuse headache (MOH) is relatively common, but its incidence has not been calculated and there are no prospective population-based studies that have evaluated risk factors for developing MOH. The aim of this study was to estimate incidences of and identify risk factors for developing chronic daily headache (CDH) and MOH. This longitudinal population-based cohort study used data from the Nord-Trøndelag Health Surveys performed in 1995-1997 and 2006-2008. Among the 51,383 participants at baseline, 41,766 were eligible approximately 11 years later. There were 26,197 participants (responder rate 63%), among whom 25,596 did not report CDH at baseline in 1995-1997. Of these, 201 (0.8%) had MOH and 246 (1.0%) had CDH without medication overuse (CDHwoO) 11 years later. The incidence of MOH was 0.72 per 1000 person-years (95% confidence interval 0.62-0.81). In the multivariate analyses, a 5-fold risk for developing MOH was found among individuals who at baseline reported regular use of tranquilizers [odds ratio 5.2 (3.0-9.0)] or who had a combination of chronic musculoskeletal complaints, gastrointestinal complaints, and Hospital Anxiety and Depression Scale score ≥ 11 [odds ratio 4.7 (2.4-9.0)]. Smoking and physical inactivity more than doubled the risk of MOH. In contrast, these factors did not increase the risk of CDHwoO. In this large population-based 11-year follow-up study, several risk factors for MOH did not increase the risk for CDHwoO, suggesting these are pathogenetically distinct. If the noted associations are causal, more focus on comorbid condition, physical activity, and use of tobacco and tranquilizers may limit the development of MOH.
 
In a previous study quantitative sensory tests were used to characterize the symptoms in patients with post-traumatic neuralgia in the hand. Two types of pain syndromes were identified, sympathetically maintained pain (SMP), and sympathetically independent pain (SIP). These two syndromes had different sensory profiles with regard to temperature discrimination and cold and heat pain thresholds. The aim of the present study was to investigate the development of symptoms 10 years later. Eighteen previously investigated patients were contacted and all answered questions concerning their symptoms. Of these, two SIP and eight SMP patients agreed to undergo quantitative sensory testing. The outcome of these tests and the patients' own reports indicated that patients with SMP, who were not repeatedly treated with sympathetic blocks, did not show any remarkable spontaneous improvement of symptoms over a decade. The SMP patients still exhibited their characteristic sensory profile with moderate impairment of temperature discrimination and allodynia to cold, heat and vibratory stimuli. However, some changes with time were observed with respect to warm-cold difference limen and vibration allodynia. Comparison with data obtained from an age-matched group of healthy individuals indicated that these changes were due to age-related factors.
 
Migraine with aura is associated with an increased incidence of stroke and cardiovascular disease, but the biological mechanisms are poorly understood. This study examined the incidence of metabolic syndrome and its relationship to migraine with and without aura and to nonmigraine headache. In the population-based the Nord-Trøndelag Health Study (HUNT), 19,895 individuals were followed for the development of metabolic syndrome, with a median follow-up time of 11.3years. Headache diagnoses were based on a validated headache questionnaire, and metabolic syndrome was based on a modified version of the National Cholesterol Education Program's Adult Treatment Panel (ATP) III criteria, using objective anthropometric measurements and blood biochemistry. Using the Poisson regression model, migraine with aura was associated with an increased risk for developing metabolic syndrome. The effect was modified by smoking, with an adjusted incident risk ratio (IRR) among smokers of 2.10 (95% CI 1.53-2.89) and among nonsmokers of 1.39 (95% CI 1.03-1.86), when compared to headache-free controls. A moderate risk increase was seen for migraine without aura (IRR 1.26, 95% CI 1.12-1.42) and nonmigraine headache (IRR 1.22, 95% CI 1.13-1.32), not modified by smoking. The results suggest that traditional risk factors may be one of the mechanisms through which migraine with aura is linked to an increased risk for cardiovascular disease. A heightened vigilance concerning cardiovascular risk factors in this patient group may be warranted.
 
It is generally acknowledged that humans display highly variable sensitivity to pain, including variable responses to identical injuries or pathologies. The possible contribution of genetic factors has, however, been largely overlooked. An emerging rodent literature documents the importance of genotype in mediating basal nociceptive sensitivity, in establishing a predisposition to neuropathic pain following neural injury, and in determining sensitivity to pharmacological agents and endogenous antinociception. One clear finding from these studies is that the effect of genotype is at least partially specific to the nociceptive assay being considered. In this report we begin to systematically describe and characterize genetic variability of nociception in a mammalian species, Mus musculus. We tested 11 readily-available inbred mouse strains (129/J, A/J, AKR/J, BALB/cJ, C3H/HeJ, C57BL/6J, C58/J, CBA/J, DBA/2J, RIIIS/J and SM/J) using 12 common measures of nociception. These included assays for thermal nociception (hot plate, Hargreaves' test, tail withdrawal), mechanical nociception (von Frey filaments), chemical nociception (abdominal constriction, carrageenan, formalin), and neuropathic pain (autotomy, Chung model peripheral nerve injury). We demonstrate the existence of clear strain differences in each assay, with 1.2 to 54-fold ranges of sensitivity. All nociceptive assays display moderate-to-high heritability (h2 = 0.30-0.76) and mediation by a limited number of apparent genetic loci. Data comparing inbred strains have considerable utility as a tool for understanding the genetics of nociception, and a particular relevance to transgenic studies.
 
Top-cited authors
Troels S Jensen
  • Aarhus University Hospital
John T Farrar
  • University of Pennsylvania
Johannes W Vlaeyen
Thomas Toelle
  • Technische Universität München
Christoph Maier
  • Ruhr-Universität Bochum