Chronic postsurgical pain: still a neglected topic?

Thirty-year survey of bibliometrics used in the research literature of pain: Analysis, evolution, and pitfalls

During the last decades, the emergence of Bibliometrics and the progress in Pain research have led to a proliferation of bibliometric studies on the medical and scientific literature of pain (B/P). This study charts the evolution of the B/P literature published during the last 30 years. Using various searching techniques, 189 B/P studies published from 1993 to August 2022 were collected for analysis-half were published since 2018. Most of the selected B/P publications use classic bibliometric analysis of Pain in toto, while some focus on specific types of Pain with Headache/Migraine, Low Back Pain, Chronic Pain, and Cancer Pain dominating. Each study is characterized by the origin (geographical, economical, institutional, …) and the medical/scientific context over a specified time span to provide a detailed landscape of the Pain research literature. Some B/P studies have been developed to pinpoint difficulties in appropriately identifying the Pain literature or to highlight some general publishing pitfalls. Having observed that most of the recent B/P studies have integrated newly emergent software visualization tools (SVTs), we found an increase of anomalies and suggest that readers exercise caution when interpreting results in the B/P literature details.

Predictors of Chronic Postsurgical Pain in Elderly Patients Undergoing Hip Arthroplasty: A Multi-Center Retrospective Cohort Study

Background

Identifying patients at high risk of developing chronic postsurgical pain (CPSP) is of extreme importance in order to help launch appropriate therapeutic strategies and intensive initiation of pain management.

Aim

In this study, we aimed to conduct a multi-center retrospective cohort study to establish a prognostic model and a nomogram to predict the risks of CPSP in elderly patients who underwent hip arthroplasty at 6 months postoperatively.

Methods

We collected data from 736 patients aged >65 years who had undergone hip arthroplasty from October 1, 2016 to September, 30, 2018 at multiple tertiary referral centers in Guangzhou, China. All data were randomly stratified into a training set and a testing set at a ratio of 8:2. Data were analyzed via multiple logistic regression analysis with receiver operating characteristic (ROC) curves and areas under the curve. This model was further validated by estimating calibration and discrimination. A nomogram was ultimately developed.

Results

A total of 736 eligible patients were enrolled, 27.20% of whom developed CPSP within 6 months postoperatively. Preoperative pain in the surgical area (OR=2.456, 95% CI:1.814–3.327, P<0.001), preoperative depression state (OR=1.256, 95% CI:1.146–1.378, P<0.001), surgical type (OR=7.138, 95% CI:3.548–14.364, P<0.001), acute postoperative numerical rating scale score (OR=5.537, 95% CI:3.607–8.499, P<0.001) and analgesic type (patient-controlled epidural analgesia: OR=0.129, 95% CI:0.055–0.299, P<0.001; patient-controlled intravenous analgesia: OR=0.033, 95% CI:0.011–0.097, P<0.001) were identified as independent significant factors associated with CPSP. A prognostic model was established and further validated. An ROC curve confirmed the predictive ability of this model with a high sensitivity value of 92.12% (95% CI:86.90–95.74) and specificity value of 91.72% (95% CI:88.77–94.11). A nomogram was developed to simplify the use of the predictive model in clinical practice.

Conclusion

This prognostic model could be of great value in clinical practice, serving as the basis for early personalized analgesic management of elderly patients undergoing hip arthroplasty.

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Neurophysiological Effects of Dorsal Root Ganglion Stimulation (DRGS) in Pain Processing at the Cortical Level

OBJECTIVES

Dorsal root ganglion stimulation (DRGS) has been used successfully against localized neuropathic pain. Nevertheless, the effects of DRGS on pain processing, particularly at the cortical level, remain largely unknown. In this study, we investigated whether positive responses to DRGS treatment would alter patients' laser-evoked potentials (LEP).

METHODS

We prospectively enrolled 12 adult patients with unilateral localized neuropathic pain in the lower limbs or inguinal region and followed them up for six months. LEPs were assessed at baseline, after one month of DRGS, and after six months of DRGS. Clinical assessment included the Numerical Rating Scale (NRS), Brief Pain Inventory (BPI), SF-36, and Beck Depression Inventory (BDI). For each patient, LEP amplitudes and latencies of the N2 and P2 components on the deafferented side were measured and compared to those of the healthy side and correlated with pain intensity, as measured with the NRS.

RESULTS

At the one- and six-month follow-ups, N2-P2 amplitudes were significantly greater and NRS scores were significantly lower compared with baseline (all p's < 0.01). There was a negative correlation between LEP amplitudes and NRS scores (r_s = -0.31, p < 0.10).

CONCLUSIONS

DRGS is able to restore LEPs to normal values in patients with localized neuropathic pain, and LEP alterations are correlated with clinical response in terms of pain intensity.

Spinal Cord Stimulation for Acute Pain Following Surgery for Cervical Myelopathy: A Novel Treatment Strategy

BACKGROUND

Chronic pain syndromes caused by degenerative and postinfectious changes in the cervical spine continue to pose significant management challenges to neurosurgeons and pain practitioners. The identification of an individualized treatment plan, astute surgical technique, comprehensive and multimodal analgesia, and adequate rehabilitation processes do not necessarily result in diminished pain.

CASE SUMMARY

We present the case of a patient with chronic pain treated surgically for degenerative cervical myelopathy secondary to cervical spinal stenosis. Following this surgery, the patient experienced an intractable postoperative pain syndrome that had anatomical borders, and an intensity and character that were different from the background chronic pain from which he suffered. We successfully implanted a cervical spinal cord stimulation (SCS) lead in the period following his stenosis surgery, which had good therapeutic effect on the postoperative-onset pain. To the best of our knowledge, this is the first description of SCS having a strong positive effect on an acute exacerbation of neuropathic pain. At follow-up 12 months later, assessment of the patient's pain diary revealed a modal pain intensity of 3/10 on the numeric rating scale over the preceding 3 months. The Brief Pain Inventory (Short Form) scores at this time were 10/40 in the pain severity domain and 18/70 in the interference with function domain, demonstrating the long-term effectiveness of this SCS strategy.

CONCLUSION

While SCS has hitherto been untested as a therapy for acute-onset pain, this report demonstrates its utility as a salvage treatment in select cases of uncontrollable postoperative pain.

Academic Journals Assessed as Springboards for New Developments: A Study of Leading Anesthesia Journals Over Past 50 Years

PURPOSE

The impact of academic journals on scientific activity can be measured using different approaches. The aim of this study was to assess the leading anesthesia journals as springboards for new developments in the field of anesthesia.

METHODS

The selection of the topics for analysis was based on the degree of increase in the number of articles on a topic that was at the center of specialty interest during 1966-2015. The assessment of a journal's response to a new development was made by measuring the number of initial articles on a related topic. Six leading anesthesia journals were assessed collectively and individually as to whether their responses to new developments were prompt and prominent.

RESULTS

The role of the leading specialty journals in presentation of 28 topics related to prominent new developments in anesthesia was found to depend on the nature of topics and the type of articles. Compared with all PubMed journals publishing articles associated with anesthesia in 1966-2015, the six leading anesthesia journals published 43% of drug-related research articles, 30% of technique-related research articles, and 16% of both drug- and technique-related review articles. Regarding initial publications (on new topics), this group of six journals contributed comparably more articles: from 43% to 84% of drug-related research articles, from 30% to 49% of technique-related research articles, from 16% to 33% of drug-related review articles, and from 16% to 25% of technique-related review articles. The approximate doubling of the shares demonstrates the dominance of this group of journals in the swiftness response to new anesthesia developments. The promptness of reaction to new developments in anesthesia of each of the six leading anesthesia journals was assessed (the combination of drug- and technique-related articles) based on the number of articles published among the first (first 5 plus next 30) on all 28 topics. The ranking order of four journals (with the highest number of all 1966-2015 articles) regarding early publications was (from high to low): Anesthesia & Analgesia, British Journal of Anaesthesia, Anesthesiology, and Anaesthesia.

CONCLUSION

This study assesses six leading anesthesia journals for their function as springboards for new developments in anesthesia over the past 50 years. The dominance of leading journals in initial publications on 28 drug-related and technique-related topics was clearly demonstrated. The results also indicate the possibility of using promptness of response to new advances for quantitative assessment of this aspect of a journal's contribution to the specialty.

Local Application of Ultrasound Attenuates Neuropathic Allodynia and Proinflammatory Cytokines in Rats After Thoracotomy

BACKGROUND AND OBJECTIVES

We aimed to investigate the effect of therapeutic ultrasound (TU) on pain sensitivity and the concentration inflammatory cytokines in a thoracotomy rat model.

METHODS

Rats were distributed randomly into 4 groups: (1) sham operated, (2) thoracotomy and rib retraction (TRR), (3) TRR rats that received TU (TRR + TU-1), and (4) TRR rats that received TU with the ultrasound turned off (TRR + TU-0). Ultrasound was set at 1-MHz frequency (1.0-W/cm intensity and 100% duty cycle for 5 minutes), began on postoperative day (POD) 10, and then continued once per day, 5 days a week for 3 weeks.

RESULTS

The TRR and TRR + TU-0 rats encountered tactile hypersensitivity from PODs 10 to 28. Mechanical withdrawal thresholds were increased (all P < 0.05) following 5 days of TU, but thresholds remained significantly lower than baseline values. Therapeutic ultrasound increased the subcutaneous, but not body temperature. All groups receiving TRR demonstrated an increase in concentration of interleukin 1β and tumor necrosis factor α (TNF-α) on POD 14; however, the rise in TNF-α concentration was less in the TU-treated group than in the others. The decrease in concentration was greatest in the TRR + TU-1 group and similar between the TRR and TRR + TU-0 groups.

CONCLUSIONS

Mechanical allodynia was partially resolved with TU. Tissue temperature increased with ultrasound, while TU restricted the up-regulation of interleukin 1β and TNF-α around the injured intercostal nerve.

Transabdominal laparoscopic retroperitoneal neurectomy for chronic pain after inguinal hernia repair and appendicectomy -a matched-pair study

Background

Chronic debilitating pain is a rare but significant cause of postoperative morbidity after inguinal surgery. Such pain is usually of neuropathic origin and frequently caused by intraoperative nerve damage. In this retrospective matched-pair study we analysed results of a minimal-invasive approach to neurectomy on quality of life and pain relief.

Methods

From March 2010 to January 2012, 9 patients developing chronic neuropathic pain after inguinal hernia repair (8 patients) or open appendicectomy (one patient) were operated using a laparoscopic transabdominal approach in our department. Clinical examinations and specific questionnaires on pain and quality of life (PainDetect, SF-36) were completed 6 months to 3 years after neurectomy. Every patient was matched with one patient without chronic pain.

Results

Seven of nine patients had severe or very severe pain before neurectomy, two had mild pain but refused a conservative treatment. Four patients were free of pain after neurectomy, three described an improved pain status, whereas two did not observe any change in pain. Within a follow-up period of 14,3 months, no deterioration of pain or other complications were observed. Patients who underwent neurectomy had significantly lower quality of life compared to the control group. No postoperative complications were observed.

Conclusions

Laparoscopic transabdominal neurectomy represents a possible surgical approach in treating patients with chronic disabling postoperative groin pain requiring surgery. This technique was feasible, safe, and effective in our series to relieve chronic debilitating pain in the majority of our patients with comparable results to other published approaches.

Predictors and trajectories of chronic postoperative pain following hip preservation surgery

Factors contributing to chronic postoperative pain (CPOP) are poorly defined in young people and developmental considerations are poorly understood. With over 5 million children undergoing surgery yearly and 25% of adults referred to chronic pain clinics identifying surgery as the antecedent, there is a need to elucidate factors that contribute to CPOP in surgical patients. The present study includes patients undergoing hip preservation surgery at a children's hospital. The HOOS and SF-12 Health Survey were administered to 614 pre-surgical patients with 421 patients completing follow-up (6-months, 1-year and 2-years post-surgery). Pain, quality of life, and functioning across time were examined for each group within the population. A three trajectory model (low pain, pain improvement and high pain) emerged indicating three categories of treatment responders. Pain trajectory groups did not differ significantly on gender, pre-surgical age, BMI, prior hip surgery, surgical type, joint congruence or Tönnis grade. The groups differed significantly from each other on pre-surgical pain, pain chronicity, quality of life and functioning. Those in the high pain and pain improvement groups endorsed having pre-surgical depression at significantly higher rates and lower pre-surgical quality of life compared to those in the low pain group (P < 0.01). Those in the high pain group reported significantly worse pre-surgical functioning compared to those in the pain improvement (P < 0.0001) and low pain groups (P < 0.0001).The results demonstrate the need for preoperative screening prior to hip preservation surgery, as there may be a subset of patients who are predisposed to chronic pain independent of hip health.

Prevention of Chronic Post-Thoracotomy Pain in Rats By Intrathecal Resolvin D1 and D2: Effectiveness of Perioperative and Delayed Drug Delivery

Thoracotomy results in a high frequency of chronic postoperative pain. Resolvins are endogenous molecules, synthesized and released by activated immune cells, effective against inflammatory and neuropathic pain. Different resolvins have differential actions on selective neuronal and glial receptors and enzymes. This article examines the ability of intrathecal resolvin D1 and resolvin D2 to reduce chronic post-thoracotomy pain in rats. Thoracotomy, involving intercostal incision and rib retraction, resulted in a decrease in the mechanical force threshold to induce nocifensive behavior, an enlargement of the pain-sensitive area, and an increase in the fraction of rats showing nocifensive behavior, all for at least 5 weeks. The qualitative nature of the behavioral responses to tactile stimulation changed dramatically after thoracotomy, including the appearance of vigorous behaviors, such as turning, shuddering, and squealing, all absent in naive rats. Intrathecal delivery of resolvin D1 (30 ng/30 μL), at surgery or 4 days later, halved the spread of the mechanosensitive area, lowered by 60% the percent of rats with tactile hypersensitivity, and reduced the drop in threshold for a nocifensive response, along with a reduction in the occurrence of vigorous nocifensive responses. Resolvin D2's actions on threshold changes were statistically the same. These findings suggest that intrathecal resolvins, delivered preoperatively or several days later, can prevent chronic postoperative hyperalgesia.

PERSPECTIVE

In studies of rats, the injection of the proresolving compounds of the resolvin-D series into spinal fluid, before or just after thoracotomy surgery, prevents the occurrence of acute and chronic pain. If these chemicals, which have shown no side-effects, were used in humans it might greatly reduce chronic postoperative pain.

Chronic postsurgical pain and neuropathic symptoms after abdominal hysterectomy: A silent epidemic

Chronic postsurgical pain (CPSP) is an important clinic problem. It is assessed that prevalence of chronic pain extends to 30% but it is contended that there are various risk factors. We aimed to evaluate the prevalence of chronic pain after hysterectomy, risk factors of chronicity, neuropathic features of pain, and sensorial alterations at surgery area.Between years 2012 and 2015, 16 to 65 ages old patients that electively undergone total abdominal hysterectomy bilateral salpingo-oophorectomy and passed minimum 3 months after surgery were included to study. Visual analog scale (VAS) and Douleur Neuropathique 4-questionnaire (DN-4) surveys were used to evaluate pain symptoms, algometry device was used for evaluating abdominal pressure threshold and Von Frey Filament was used for sensorial alterations.Ninety-three of 165 eligible patients were included to study. As the groups were compared by demographic data, no difference was obtained (P > 0.05). There was no difference between groups regarding patient and surgery attributes (P > 0.05). Most frequently performed incision type was Pfannenstiel. Neuropathic symptoms were observed in 90 patients (96.8%). Sensorial alterations as hypoesthesia and hyperesthesia were detected around abdominal scar in 18 patients (19.4%) with pinprick test.Neuropathic symptoms should not be ignored in studies evaluating CPSP and a standard methodology should be designed for studies in this topic.

Spontaneous Chronic Pain After Experimental Thoracotomy Revealed by Conditioned Place Preference: Morphine Differentiates Tactile Evoked Pain From Spontaneous Pain

Chronic pain after surgery limits social activity, interferes with work, and causes emotional suffering. A major component of such pain is reported as resting or spontaneous pain with no apparent external stimulus. Although experimental animal models can simulate the stimulus-evoked chronic pain that occurs after surgery, there have been no studies of spontaneous chronic pain in such models. Here the conditioned place preference (CPP) paradigm was used to reveal resting pain after experimental thoracotomy. Male Sprague Dawley rats received a thoracotomy with 1-hour rib retraction, resulting in evoked tactile hypersensitivity, previously shown to last for at least 9 weeks. Intraperitoneal injections of morphine (2.5 mg/kg) or gabapentin (40 mg/kg) gave equivalent 2- to 3-hour-long relief of tactile hypersensitivity when tested 12 to 14 days postoperatively. In separate experiments, single trial CPP was conducted 1 week before thoracotomy and then 12 days (gabapentin) or 14 days (morphine) after surgery, followed the next day by 1 conditioning session with morphine or gabapentin, both versus saline. The gabapentin-conditioned but not the morphine-conditioned rats showed a significant preference for the analgesia-paired chamber, despite the equivalent effect of the 2 agents in relieving tactile allodynia. These results show that experimental thoracotomy in rats causes spontaneous pain and that some analgesics, such as morphine, that reduce evoked pain do not also relieve resting pain, suggesting that pathophysiological mechanisms differ between these 2 aspects of long-term postoperative pain. Perspective: Spontaneous pain, a hallmark of chronic postoperative pain, is demonstrated here in a rat model of experimental postthoracotomy pain, further validating the use of this model for the development of analgesics to treat such symptoms. Although stimulus-evoked pain was sensitive to systemic morphine, spontaneous pain was not, suggesting different mechanistic underpinnings.

Scientometrics of drug discovery efforts: pain-related molecular targets

The aim of this study was to make a scientometric assessment of drug discovery efforts centered on pain-related molecular targets. The following scientometric indices were used: the popularity index, representing the share of articles (or patents) on a specific topic among all articles (or patents) on pain over the same 5-year period; the index of change, representing the change in the number of articles (or patents) on a topic from one 5-year period to the next; the index of expectations, representing the ratio of the number of all types of articles on a topic in the top 20 journals relative to the number of articles in all (>5,000) biomedical journals covered by PubMed over a 5-year period; the total number of articles representing Phase I–III trials of investigational drugs over a 5-year period; and the trial balance index, a ratio of Phase I–II publications to Phase III publications. Articles (PubMed database) and patents (US Patent and Trademark Office database) on 17 topics related to pain mechanisms were assessed during six 5-year periods from 1984 to 2013. During the most recent 5-year period (2009–2013), seven of 17 topics have demonstrated high research activity (purinergic receptors, serotonin, transient receptor potential channels, cytokines, gamma aminobutyric acid, glutamate, and protein kinases). However, even with these seven topics, the index of expectations decreased or did not change compared with the 2004–2008 period. In addition, publications representing Phase I–III trials of investigational drugs (2009–2013) did not indicate great enthusiasm on the part of the pharmaceutical industry regarding drugs specifically designed for treatment of pain. A promising development related to the new tool of molecular targeting, ie, monoclonal antibodies, for pain treatment has not yet resulted in real success. This approach has not yet demonstrated clinical effectiveness (at least with nerve growth factor) much beyond conventional analgesics, when its potential cost is more than an order of magnitude higher than that of conventional treatments. This scientometric assessment demonstrated a lack of real breakthrough developments.

A review of the literature on multiple factors involved in postoperative pain course and duration

OBJECTIVE

To review the literature on the progression from acute to chronic postoperative pain, to evaluate the evidence for the risk of progressing to persistent postoperative and chronic pain, and to identify characteristics of pharmacologic treatments to best tailor therapy to an individual patient's pain profile.

BACKGROUND

Pain is most commonly classified by duration (acute, chronic) and pathophysiology (nociceptive, neuropathic); however, these descriptors alone incompletely describe pain. Additionally, the transition between acute and chronic postoperative pain is not well understood.

METHODS

We conducted a qualitative review and evaluation of the literature on postoperative pain with respect to the above objectives.

RESULTS

Individualized pharmacologic treatments require a complete characterization of a patient's pain profile, in terms of frequency of pain over the course of a 24-hour day and over time thereafter, frequency and duration of pain flares, and presence of neuropathic pain. These considerations can help guide the choice of pharmacologic treatment to meet patient needs over a 24-hour day and over time after surgery. With respect to opioid analgesics, acute pain requires rapid onset of analgesia and the ability to titrate analgesia to the changing characteristics of pain over a short period. For these reasons, short-acting opioid analgesics have been preferred; however, there are opioid formulations with rapid onset and extended release for reduced dosing frequency. Although nociceptive pain can typically be controlled by titration of the dose of an opioid analgesic, neuropathic pain may respond better to the addition of an antineuropathic medication rather than to opioid dose escalation.

CONCLUSION

Advances in individualized pharmacologic treatment for postoperative pain have resulted in better pain control. Moreover, the recognition of sub-acute pain as a new entity is important because many surgical patients will need therapy beyond the first 8 days after surgery. In this group of patients the diagnosis of a neuropathic pain component will be important so that appropriate multimodal therapy may be implemented.

Risk factors and early pharmacological interventions to prevent chronic postsurgical pain following cardiac surgery

Chronic postsurgical pain (CPSP) after cardiac surgery represents a significant clinical problem. The prevalence of CPSP varies widely between studies, but severe CPSP is present in less than 10% of the patients. Important differential diagnoses for CPSP after cardiac surgery are myocardial ischemia, sternal instability and mediastinitis. CPSP after cardiac surgery may be thoracic pain present at the site of the sternotomy or leg pain due to vein-graft harvesting. The CPSP can be neuropathic pain, visceral pain, somatic pain or mixed pain. Potential risk factors for CPSP are young age, female gender, overweight, psychological factors, preoperative pain, surgery-related factors and severe postoperative pain. In addition to standard postoperative analgesics, the use of N-methyl-D-aspartate (NMDA) antagonists, alpha-2 agonists, local anesthetics, gabapentinoids, and corticosteroids are all proposed to reduce the risk for CPSP after cardiac surgery. Still, no specific pharmacological therapy, cognitive therapy or physical therapy is established to protect against CPSP. The only convincing prevention of CSPS is adequate treatment of acute postoperative pain irrespective of method. Hence, interventions against acute pain, preferably in a step-wise approach titrating the interventions for each patient's individual needs, are essential concerning prevention of CPSP after cardiac surgery. It is also important that surgeons consider the risk for CPSP as a part of the basis for decision-making around performing a surgical procedure and that patients are informed of this risk.

Pain prevalence and trajectories following pediatric spinal fusion surgery

Factors contributing to pain following surgery are poorly understood, with previous research largely focused on adults. With approximately 6 million children undergoing surgery each year, there is a need to study pediatric persistent postsurgical pain. The present study includes patients with adolescent idiopathic scoliosis undergoing spinal fusion surgery enrolled in a prospective, multicentered registry examining postsurgical outcomes. The Scoliosis Research Society Questionnaire-Version 30, which includes pain, activity, mental health, and self-image subscales, was administered to 190 patients prior to surgery and at 1 and 2 years postsurgery. A subset (n = 77) completed 5-year postsurgery data. Pain prevalence at each time point and longitudinal trajectories of pain outcomes derived from SAS PROC TRAJ were examined using analyses of variance and post hoc pairwise analyses across groups. Thirty-five percent of patients reported pain in the moderate to severe range presurgery. One year postoperation, 11% reported pain in this range, whereas 15% reported pain at 2 years postsurgery. At 5 years postsurgery, 15% of patients reported pain in the moderate to severe range. Among the 5 empirically derived pain trajectories, there were significant differences on self-image, mental health, and age. Identifying predictors of poor long-term outcomes in children with postsurgical pain may prevent the development of chronic pain into adulthood.

PERSPECTIVE

This investigation explores the prevalence of pediatric pain following surgery, up to 5 years after spinal fusion surgery. Five pain trajectories were identified and were distinguishable on presurgical characteristics of age, mental health, and self-image. This is the largest study to examine longitudinal pediatric pain trajectories after surgery.

The Qualitative Hyperalgesia Profile: A New Metric to Assess Chronic Post-Thoracotomy Pain

Thoracotomy often results in chronic pain, characterized by resting pain and elevated mechano-sensitivity. This paper defines complex behavioral responses to tactile stimulation in rats after thoracotomy, shown to be reversibly relieved by systemic morphine, in order to develop a novel qualitative "pain" score. A deep incision and 1 hour of rib retraction in male Sprague-Dawley rats resulted in reduced threshold and a change in the locus of greatest tactile (von Frey filament) sensitivity, from the lower back to a more rostral location around the wound site, and extending bilaterally. The fraction of rats showing nocifensive responses to mild stimulation (10 gm) increased after thoracotomy (from a pre-operative value of 0/10 to 8/10 at 10 days post-op), and the average threshold decreased correspondingly, from 15 gm to ∼4 gm. The nature of the nocifensive responses to tactile stimulation, composed pre-operatively only of no response (Grade 0) or brief contractions of the local subcutaneous muscles (Grade I), changed markedly after thoracotomy, with the appearance of new behaviors including a brisk lateral "escape" movement and/or a 180° rotation of the trunk (both included as Grade II), and whole body shuddering, and scratching and squealing (Grade III). Systemic morphine (2.5 mg/kg, i.p.) transiently raised the threshold for response and reduced the frequency of Grade II and III responses, supporting the interpretation that these represent pain. The findings support the development of a Qualitative Hyperalgesic Profile to assess the complex behavior that indicates a central integration of hyperalgesia.

Long-term opioid treatment of chronic nonmalignant pain: unproven efficacy and neglected safety?

BACKGROUND

For the past 30 years, opioids have been used to treat chronic nonmalignant pain. This study tests the following hypotheses: (1) there is no strong evidence-based foundation for the conclusion that long-term opioid treatment of chronic nonmalignant pain is effective; and (2) the main problem associated with the safety of such treatment - assessment of the risk of addiction - has been neglected.

METHODS

Scientometric analysis of the articles representing clinical research in this area was performed to assess (1) the quality of presented evidence (type of study); and (2) the duration of the treatment phase. The sufficiency of representation of addiction was assessed by counting the number of articles that represent (1) editorials; (2) articles in the top specialty journals; and (3) articles with titles clearly indicating that the addiction-related safety is involved (topic-in-title articles).

RESULTS

Not a single randomized controlled trial with opioid treatment lasting >3 months was found. All studies with a duration of opioid treatment ≥6 months (n = 16) were conducted without a proper control group. Such studies cannot provide the consistent good-quality evidence necessary for a strong clinical recommendation. There were profound differences in the number of addiction articles related specifically to chronic nonmalignant pain patients and to opioid addiction in general. An inadequate number of chronic pain-related publications were observed with all three types of counted articles: editorials, articles in the top specialty journals, and topic-in-title articles.

CONCLUSION

There is no strong evidence-based foundation for the conclusion that long-term opioid treatment of chronic nonmalignant pain is effective. The above identified signs indicating neglect of addiction associated with the opioid treatment of chronic nonmalignant pain were present.