Intrathecal administration of conditioned serum from different species resolves Chemotherapy-Induced neuropathic pain in mice via secretory exosomes.

Chemotherapy-induced peripheral neuropathy (CIPN) is the most prevalent neurological complication of chemotherapy for cancer, and has limited effective treatment options. Autologous conditioned serum (ACS) is an effective biologic therapy used by intra-articular injection for patients with osteoarthritis. However, ACS has not been systematically tested in the treatment of peripheral neuropathies such as CIPN. It has been generally assumed that the analgesic effect of this biologic therapy results from augmented concentrations of anti-inflammatory cytokines and growth factors. Here we report that a single intrathecal injection of human conditioned serum (hCS) produced long-lasting inhibition of paclitaxel chemotherapy-induced neuropathic pain (mechanical allodynia) in mice, without causing motor impairment. Strikingly, the analgesic effect of hCS in our experiments was maintained even 8 weeks after the treatment, compared with non-conditioned human serum (hNCS). Furthermore, the hCS transfer-induced pain relief in mice was fully recapitulated by rat or mouse CS transfer to mice of both sexes, indicating cross-species and cross-sex effectiveness. Mechanistically, CS treatment blocked the chemotherapy-induced glial reaction in the spinal cord and improved nerve conduction. Compared to NCS, CS contained significantly higher concentrations of anti-inflammatory and pro-resolving mediators, including IL-1Ra, TIMP-1, TGF-ß1, and resolvins D1/D2. Intrathecal injection of anti-TGF-ß1 and anti-Il-1Ra antibody transiently reversed the analgesic action of CS. Nanoparticle tracking analysis revealed that rat conditioned serum contained a significantly greater number of exosomes than NCS. Importantly, the removal of exosomes by high-speed centrifugation largely diminished the CS-produced pain relief, suggesting a critical involvement of small vesicles (exosomes) in the beneficial effects of CS. Together, our findings demonstrate that intrathecal CS produces a remarkable resolution of neuropathic pain mediated through a combination of small vesicles/exosomes and neuroimmune/neuroglial modulation.

Epidural blood patch: A narrative review.

The epidural blood patch (EBP) is one of the most effective treatments for intracranial hypotension. Anesthesiologists are familiar with performing EBPs for the treatment of dural puncture-associated intracranial hypotension following spinal anesthesia, complicated epidural analgesia, and diagnostic lumbar puncture. Increasingly, EBPs are used to treat patients with spontaneous intracranial hypotension. However, the treatment of these non-iatrogenic conditions presents new therapeutic challenges. The purpose of this narrative review is to discuss both procedural and diagnostic considerations of EBP for the various presentations of intracranial hypotension and allow the clinician to tailor treatment for the patient, especially in the setting of diagnostic dilemmas. After discussing EBP history and relevant anatomy, we review mechanisms of action and clinical indications for this intervention. The contraindications, complications, and treatment alternatives to the blood patch are examined in detail. Finally, objective methods to evaluate the effectiveness of the EBP, such as MRI or Doppler ultrasound, are presented as novel methods that may improve future diagnostic accuracy and treatment success.

Phenotypic profile clustering pragmatically identifies diagnostically and mechanistically informative subgroups of chronic pain patients.

ABSTRACT: Traditional classification and prognostic approaches for chronic pain conditions focus primarily on anatomically based clinical characteristics not based on underlying biopsychosocial factors contributing to perception of clinical pain and future pain trajectories. Using a supervised clustering approach in a cohort of temporomandibular disorder cases and controls from the Orofacial Pain: Prospective Evaluation and Risk Assessment study, we recently developed and validated a rapid algorithm (ROPA) to pragmatically classify chronic pain patients into 3 groups that differed in clinical pain report, biopsychosocial profiles, functional limitations, and comorbid conditions. The present aim was to examine the generalizability of this clustering procedure in 2 additional cohorts: a cohort of patients with chronic overlapping pain conditions (Complex Persistent Pain Conditions study) and a real-world clinical population of patients seeking treatment at duke innovative pain therapies. In each cohort, we applied a ROPA for cluster prediction, which requires only 4 input variables: pressure pain threshold and anxiety, depression, and somatization scales. In both complex persistent pain condition and duke innovative pain therapies, we distinguished 3 clusters, including one with more severe clinical characteristics and psychological distress. We observed strong concordance with observed cluster solutions, indicating the ROPA method allows for reliable subtyping of clinical populations with minimal patient burden. The ROPA clustering algorithm represents a rapid and valid stratification tool independent of anatomic diagnosis. ROPA holds promise in classifying patients based on pathophysiological mechanisms rather than structural or anatomical diagnoses. As such, this method of classifying patients will facilitate personalized pain medicine for patients with chronic pain.

Neuroimmune modulation of pain and regenerative pain medicine.

Regenerative pain medicine, which seeks to harness the body's own reparative capacity, is rapidly emerging as a field within pain medicine and orthopedics. It is increasingly appreciated that common analgesic mechanisms for these treatments depend on neuroimmune modulation. In this Review, we discuss recent progress in mechanistic understanding of nociceptive sensitization in chronic pain with a focus on neuroimmune modulation. We also examine the spectrum of regenerative outcomes, including preclinical and clinical outcomes. We further distinguish the analgesic mechanisms of regenerative therapies from those of cellular replacement, creating a conceptual and mechanistic framework to evaluate future research on regenerative medicine.

Impact of an Opioid Safety Initiative on Patients Undergoing Total Knee Arthroplasty: A Time Series Analysis.

BACKGROUND: The Opioid Safety Initiative decreased high-dose prescriptions across the Veterans Health Administration. This study sought to examine the impact of this intervention (i.e., the Opioid Safety Initiative) on pain scores and opioid prescriptions in patients undergoing total knee arthroplasty. METHODS: This was an ecological study of group-level data among 700 to 850 patients per month over 72 consecutive months (January 2010 to December 2015). The authors examined characteristics of cohorts treated before versus after rollout of the Opioid Safety Initiative (October 2013). Each month, the authors aggregated at the group-level the differences between mean postoperative and preoperative pain scores for each patient (averaged over 6-month periods), and measured proportions of patients (per 1,000) with opioid (and nonopioid) prescriptions for more than 3 months in 6-month periods, preoperatively and postoperatively. The authors compared postintervention trends versus trends forecasted based on preintervention measures. RESULTS: After the Opioid Safety Initiative, patients were slightly older and sicker, but had lower mortality rates (postintervention n = 28,509 vs. preintervention n = 31,547). Postoperative pain scores were slightly higher and the decrease in opioid use was statistically significant, i.e., 871 (95% CI, 474 to 1,268) fewer patients with chronic postoperative prescriptions. In time series analyses, mean postoperative minus preoperative pain scores had increased from 0.65 to 0.81, by 0.16 points (95% CI, 0.05 to 0.27). Proportions of patients with chronic postoperative and chronic preoperative opioid prescriptions had declined by 20% (n = 3,355 vs. expected n = 4,226) and by 13% (n = 5,861 vs. expected n = 6,724), respectively. Nonopioid analgesia had increased. Sensitivity analyses confirmed all findings. CONCLUSIONS: A system-wide initiative combining guideline dissemination with audit and feedback was effective in significantly decreasing opioid prescriptions in populations undergoing total knee arthroplasty, while minimally impacting pain scores.

The Impact of Surgical Amputation and Valproic Acid on Pain and Functional Trajectory: Results from the Veterans Integrated Pain Evaluation Research (VIPER) Randomized, Double-Blinded Placebo-Controlled Trial.

OBJECTIVE: To determine if the perioperative administration of valproic acid reduces the incidence of chronic pain three months after amputation or revision surgery. DESIGN: Multicenter, randomized, double-blind, placebo-controlled trial. SETTING: Academic, military, and veteran medical centers. SUBJECTS: One hundred twenty-eight patients undergoing amputation or amputation revision surgery at Duke University Hospital, Walter Reed National Military Medical Center, or the Durham Veterans Affairs Medical Center for either medical disease or trauma. METHODS: Patients were randomized to placebo or valproic acid for the duration of hospitalization and treated with multimodal analgesic care, including regional anesthetic blockade. Primary outcome was the proportion of patients with chronic pain at three months (average numeric pain score intensity of 3/10 or greater). Secondary outcomes included functional trajectories (assessed with the Brief Pain Inventory short form and the Defense and Veterans Pain Rating Scale). RESULTS: The overall rate of chronic pain was 68.2% in the 107 patients who completed the end point assessment. There was no significant effect of perioperative valproic acid administration, with a rate of 65.45% (N = 36) in the treatment group and a rate of 71.15% (N = 37) in the placebo group. Overall, pain scores decreased from baseline to follow-up (median = -2 on the numeric pain scale). Patients additionally experienced improvements in self-perceived function. CONCLUSIONS: The rate of chronic pain after amputation surgery is not significantly improved with the perioperative administration of valproic acid. In this cohort treated with multimodal perioperative analgesia and regional anesthetic blockade, we observed improvements in both pain severity and function.

DNA methylation profiles are associated with complex regional pain syndrome after traumatic injury.

Factors contributing to development of complex regional pain syndrome (CRPS) are not fully understood. This study examined possible epigenetic mechanisms that may contribute to CRPS after traumatic injury. DNA methylation profiles were compared between individuals developing CRPS (n = 9) and those developing non-CRPS neuropathic pain (n = 38) after undergoing amputation following military trauma. Linear Models for Microarray (LIMMA) analyses revealed 48 differentially methylated cytosine-phosphate-guanine dinucleotide (CpG) sites between groups (unadjusted P's < 0.005), with the top gene COL11A1 meeting Bonferroni-adjusted P < 0.05. The second largest differential methylation was observed for the HLA-DRB6 gene, an immune-related gene linked previously to CRPS in a small gene expression study. For all but 7 of the significant CpG sites, the CRPS group was hypomethylated. Numerous functional Gene Ontology-Biological Process categories were significantly enriched (false discovery rate-adjusted q value <0.15), including multiple immune-related categories (eg, activation of immune response, immune system development, regulation of immune system processes, and antigen processing and presentation). Differentially methylated genes were more highly connected in human protein-protein networks than expected by chance (P < 0.05), supporting the biological relevance of the findings. Results were validated in an independent sample linking a DNA biobank with electronic health records (n = 126 CRPS phenotype, n = 19,768 non-CRPS chronic pain phenotype). Analyses using PrediXcan methodology indicated differences in the genetically determined component of gene expression in 7 of 48 genes identified in methylation analyses (P's < 0.02). Results suggest that immune- and inflammatory-related factors might confer risk of developing CRPS after traumatic injury. Validation findings demonstrate the potential of using electronic health records linked to DNA for genomic studies of CRPS.

Acute Pain Is Associated With Chronic Opioid Use After Total Knee Arthroplasty.

BACKGROUND AND OBJECTIVES: Pain scores are routinely reported in clinical practice, and we wanted to examine whether this routinely measured, patient-reported variable provides prognostic information, especially with regard to chronic opioid use, after taking preoperative and perioperative variables into account in a preoperative opioid user population. METHODS: In 32,874 preoperative opioid users undergoing primary total knee arthroplasty at Veterans Affairs hospitals between 2010 and 2015, we compared preoperative and perioperative characteristics in patients reporting lower versus higher acute pain (scores ≤4/10 vs >4/10 averaged over days 1-3). We calculated the propensity for lower acute pain based on all available data. After 1:1 propensity score matching, to identify similar patients differing only in acute pain, we contrasted rates of chronic significant opioid use (mean >30 mg/d in morphine equivalents) beyond postoperative month 3, discharge prescriptions, and changes in postoperative versus preoperative dose categories. Sensitivity analysis examined associations with dose escalation. RESULTS: Rates of chronic significant opioid use (21% overall) differed in patients with lower versus higher acute pain (36% vs 64% of the overall cohort). After propensity matching (total n = 20,926 patients) and adjusting for all significant factors, lower acute pain was associated with less chronic significant opioid use (rates 12% vs 16%), smaller discharge prescriptions (ie, supply <30 days and daily oral morphine equivalent <30 mg/d), and more reduction in dose, all P < 0.001. In sensitivity analysis, dose escalation was 15% less likely with lower acute pain (odds ratio, 0.85; 95% confidence interval, 0.80-0.91). CONCLUSIONS: Acute pain predicts chronic opioid use. Prospective studies of efforts to reduce acute pain, in terms of long-term effects, are needed.

Opioid exposure is associated with nonunion risk in a traumatically injured population: An inception cohort study.

INTRODUCTION: Certain common medications are associated with an elevated risk of fracture and recent data suggests that medications can also increase nonunion risk. Medication use is a modifiable nonunion risk factor, but it is unknown whether risk accrues solely to chronic medication use or whether there is also risk inherent to acute use. METHODS: Multivariate logistic regression was used in an inception cohort to calculate odds ratios (OR) for fracture nonunion associated with medication use, in context with other risk factors demonstrated to influence nonunion. Patient-level health claims for medical and drug expenses were compiled from a payer database. Patients were included if they had a fracture coded in 2011, with continuous enrollment for 1 month prior to and 12 months after fracture. The database contained demographic descriptors, treatment procedures per CPT codes, co-morbidities per ICD-9 codes, and prescriptions per National Drug Codes. Chronic medication use was defined as ≥30 days of prescription prior to fracture with ≥1 day afterward; acute use was any other prescription. RESULTS: Most non-analgesic medications were safe in acute or chronic use, but risk of nonunion was elevated for a wide range of analgesics. Overall, 45,085 fractures (14.6% of fractures) affected patients using chronic opioids. Nonunion OR was elevated for acute and chronic use of Schedule 2 opioids including acetaminophen/oxycodone, hydromorphone, oxycodone, and acetaminophen/hydrocodone bitartrate, as well as Schedule 3-5 opioids including tramadol (all, p < 0.0001). The highest ORs were associated with chronic administration of Schedule 2 opioids. DISCUSSION: Most medications do not increase nonunion risk, but acute and chronic use of NSAIDs or opioids was associated with impaired fracture healing. There is particular risk in prescribing opioid analgesics for fracture, though literature suggests that roughly half of opioid-naïve patients receive such a prescription. CONCLUSIONS: Patients evaluated in this study were not a random sample of Americans; they may approximate a random sample of the Emergency Department population in the United States. Thus, trauma patients may represent a population enriched for nonunion risk factors. Opioids impair recovery from injury; if they also predispose to injury, the ongoing opioid epidemic could presage an increase in nonunion prevalence.

Acupuncture for chronic pain: an update and critical overview.

PURPOSE OF REVIEW: Acupuncture is now recommended for several chronic pain conditions. Despite supportive evidence of its effectiveness, this ancient approach is often misunderstood, and may still be underused in mainstream practice. A critical review on its effectiveness and practice integration, and mechanisms of action is essential to the medical community that is continuing to seek nonopioid therapies for chronic pain. RECENT FINDINGS: Mounting evidence supports the effectiveness of acupuncture to treat chronic low back, neck, shoulder, and knee pain, as well as headaches. Additional data are emerging that support the use of acupuncture as an adjunct or alternative to opioids, and in perioperative settings. Findings related to its mechanisms of action include transient receptor potential cation channel vanilloid 1 activation in the periphery, microglial suppression in the cerebral cortex and spinal cord, and regulation of cytokines and other key inflammatory factors in the spinal cord. Incremental integration of acupuncture into pain medicine practices and training programmes continues to grow. SUMMARY: Acupuncture is effective, safe, and cost-effective for treating several chronic pain conditions when performed by well-trained healthcare professionals. Further studies on its use as an adjunct or alternative to opioids, and in perioperative settings are needed.

5-Hydroxymethylcytosine (5hmC) and Ten-eleven translocation 1-3 (TET1-3) proteins in the dorsal root ganglia of mouse: Expression and dynamic regulation in neuropathic pain.

Epigenetic mechanisms are increasingly implicated in chronic pain pathology. In this study, we demonstrate that the novel epigenetic mark 5-hydroxymethylcytosine (5hmC) is present in dorsal root ganglia (DRG) neurons and glia, and its levels increase following nerve injury. Furthermore, we show that the 5hmC-generating Ten-eleven translocation 1-3 (TET1-3) proteins are expressed in a cell-type specific manner in the DRG, with Tet3 displaying differential upregulation after injury, suggesting a potential role in neuropathic pain.

Perioperative Pain Management Strategies for Amputation: A Topical Review.

Objective: To review acute pain management strategies in patients undergoing amputation with consideration of preoperative patient factors, pharmacologic/interventional modalities, and multidisciplinary care models to alleviate suffering in the immediate post-amputation setting. Background: Regardless of surgical indication, patients undergoing amputation suffer from significant residual limb pain and phantom limb pain in the acute postoperative phase. Most studies have primarily focused on strategies to prevent persistent pain with inclusion of immediate postoperative outcomes as secondary measures. Pharmacologic agents, including gabapentin, ketamine, and calcitonin, and interventional modalities such as neuraxial and perineural catheters, have been examined in the perioperative period. Design: Focused Literature Review. Results: Pharmacologic agents (gabapentin, ketamine, calcitonin) have not shown consistent efficacy. Neuraxial analgesia has demonstrated both an opioid sparing and analgesic benefit while results have been mixed regarding perineural catheters in the immediate post-amputation setting. However, several early studies of perineural catheters employed sub-optimal techniques (distal surgical placement), and prolonged use of perineural catheters may provide a sustained benefit. Regardless of analgesic technique, a multidisciplinary approach is necessary for optimal care. Conclusion: Patient-tailored analgesic regimens utilizing catheter-based techniques are essential in the acute post-amputation phase and should be implemented in all patients undergoing amputation. Future research should focus on improved measurement of acute pain and comparisons of effective analgesic regimens instead of single techniques.

Differential expression of systemic inflammatory mediators in amputees with chronic residual limb pain.

Chronic postsurgical pain impacts most amputees, with more than half experiencing neuralgic residual limb pain. The transition from normal acute postamputation pain to chronic residual limb pain likely involves both peripheral and central inflammatory mechanisms. As part of the Veterans Integrated Pain Evaluation Research study, we investigated links between systemic inflammatory mediator levels and chronic residual limb pain. Subjects included 36 recent active duty military traumatic amputees with chronic residual limb pain and 40 without clinically significant pain. Blood samples were obtained and plasma concentrations of an array of inflammatory mediators were analyzed. Residual limb pain intensity and pain catastrophizing were assessed to examine associations with inflammatory mediators. Pro-inflammatory mediators including tumor necrosis factor (TNF)-α, TNF-ß, interleukin (IL)-8, ICAM-1, Tie2, CRP, and SAA were elevated in patients with chronic residual limb pain. Across all patients, residual limb pain intensity was associated positively with levels of several proinflammatory mediators (IL-8, TNF-α, IL-12, TNF-ß, PIGF, Tie2, SAA, and ICAM-1), and inversely with concentrations of the anti-inflammatory mediator IL-13, as well as IL-2 and Eotaxin-3. Pain catastrophizing correlated positively with IL-8, IL-12, TNF-ß, PIGF, and ICAM-1, and inversely with IL-13. Significant associations between catastrophizing and residual limb pain intensity were partially mediated by TNF-α, TNF- ß, SAA, and ICAM-1 levels. Results suggest that chronic postamputation residual limb pain is associated with excessive inflammatory response to injury or to inadequate resolution of the postinjury inflammatory state. Impact of pain catastrophizing on residual limb pain may be because of part to common underlying inflammatory mechanisms.

Pain Phenotypes and Associated Clinical Risk Factors Following Traumatic Amputation: Results from Veterans Integrated Pain Evaluation Research (VIPER).

OBJECTIVE: To define clinical phenotypes of postamputation pain and identify markers of risk for the development of chronic pain. DESIGN: Cross-sectional study of military service members enrolled 3-18 months after traumatic amputation injury. SETTING: Military Medical Center. SUBJECTS: 124 recent active duty military service members. METHODS: Study subjects completed multiple pain and psychometric questionnaires to assess the qualities of phantom and residual limb pain. Medical records were reviewed to determine the presence/absence of a regional catheter near the time of injury. Subtypes of residual limb pain (somatic, neuroma, and complex regional pain syndrome) were additionally analyzed and associated with clinical risk factors. RESULTS: A majority of enrolled patients (64.5%) reported clinically significant pain (pain score ≥ 3 averaged over previous week). 61% experienced residual limb pain and 58% experienced phantom pain. When analysis of pain subtypes was performed in those with residual limb pain, we found evidence of a sensitized neuroma in 48.7%, somatic pain in 40.8%, and complex regional pain syndrome in 19.7% of individuals. The presence of clinically significant neuropathic residual limb pain was associated with symptoms of PTSD and depression. Neuropathic pain of any severity was associated with symptoms of all four assessed clinical risk factors: depression, PTSD, catastrophizing, and the absence of regional analgesia catheter. CONCLUSIONS: Most military service members in this cohort suffered both phantom and residual limb pain following amputation. Neuroma was a common cause of neuropathic pain in this group. Associated risk factors for significant neuropathic pain included PTSD and depression. PTSD, depression, catastrophizing, and the absence of a regional analgesia catheter were associated with neuropathic pain of any severity.

Evaluating Deformation-Induced Grain Orientation Change in a Polycrystal During In Situ Tensile Deformation using EBSD.

Using an in situ load frame within a scanning electron microscope, a microstructural section on the surface of an annealed tantalum (Ta) polycrystalline specimen was mapped at successive tensile strain intervals, up to ~20% strain, using electron backscatter diffraction. A grain identification and correlation technique was developed for characterizing the evolving microstructure during loading. Presenting the correlated results builds on the reference orientation deviation (ROD) map concept where individual orientation measurements within a grain are compared with a reference orientation associated with that grain. In this case, individual orientation measurements in a deformed grain are measured relative to a reference orientation derived from the undeformed (initial) configuration rather than the current deformed configuration as has been done for previous ROD schemes. Using this technique helps reveal the evolution of crystallographic orientation gradients and development of deformation-induced substructure within grains. Although overall crystallographic texture evolved slowly during deformation, orientation spread within grains developed quickly. In some locations, misorientation relative to the original orientation of a grain exceeded 20° by 15% strain. The largest orientation changes often appeared near grain boundaries suggesting that these regions were preferred locations for the initial development of subgrains.

Residual limb pain is not a diagnosis: a proposed algorithm to classify postamputation pain.

BACKGROUND: Although postamputation pain (PAP) syndromes have been described since the 16th century, taxonomy of these conditions remains ill-defined. The term "Residual Limb Pain" fails to distinguish between distinct diagnostic entities such as neuroma, complex regional pain syndrome, and somatic pathology. Even phantom limb pain (PLP), although easily distinguished from residual limb pain (RLP), has not been consistently delineated from other PAP syndromes. METHODS: A systematic review of the literature was conducted to identify the degree of delineation of various post amputation pain states and what diagnostic criteria were utilized if any. Furthermore, papers that involved treatment modalities were reviewed to determine efficacy of treatment. RESULTS: Of the 151 papers reviewed, none further categorized RLP into more specific diagnostic criteria. Furthermore, the literature contains numerous case reports, case series, letters to the editors, and grossly underpowered studies demonstrating significant positive results, yet few high-quality randomized controlled trials. CONCLUSIONS: Describing and defining the distinct clinical entities, intuitively, is a prerequisite to developing optimal treatments. The reported variation in the incidence of PAP phenomena may well represent inconsistency in assessment tools and diagnostic categories rather than variation in prevalence of these conditions. In this paper, we review the historical evolution of the current understanding of these syndromes and propose an algorithm for uniform classification.

Epigenetics and the transition from acute to chronic pain.

OBJECTIVE: The objective of this study was to review the epigenetic modifications involved in the transition from acute to chronic pain and to identify potential targets for the development of novel, individualized pain therapeutics. BACKGROUND: Epigenetics is the study of heritable modifications in gene expression and phenotype that do not require a change in genetic sequence to manifest their effects. Environmental toxins, medications, diet, and psychological stresses can alter epigenetic processes such as DNA methylation, histone acetylation, and RNA interference. As epigenetic modifications potentially play an important role in inflammatory cytokine metabolism, steroid responsiveness, and opioid sensitivity, they are likely key factors in the development of chronic pain. Although our knowledge of the human genetic code and disease-associated polymorphisms has grown significantly in the past decade, we have not yet been able to elucidate the mechanisms that lead to the development of persistent pain after nerve injury or surgery. DESIGN: This is a focused literature review of epigenetic science and its relationship to chronic pain. RESULTS: Significant laboratory and clinical data support the notion that epigenetic modifications are affected by the environment and lead to differential gene expression. Similar to mechanisms involved in the development of cancer, neurodegenerative disease, and inflammatory disorders, the literature endorses an important potential role for epigenetics in chronic pain. CONCLUSIONS: Epigenetic analysis may identify mechanisms critical to the development of chronic pain after injury, and may provide new pathways and target mechanisms for future drug development and individualized medicine.