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Cancer diagnosis and treatment are drastic events for patients and their families. Besides psychological aspects of the disease, patients are often affected by severe side effects related to the cancer itself or as a result of therapeutic interventions. Particularly, chemotherapy-induced peripheral neuropathy (CIPN) is the most prevalent neurological complication of oral or intravenous chemotherapy. The disorder may require dose reduction of chemotherapy and is accompanied by multiple symptoms with long-term functional impairment affecting quality of life (QoL), e.g., sensory and functional deteriorations as well as severe pain. Although CIPN may reverse or improve after termination of the causative chemotherapy, approximately 30-40% of patients are faced with chronicity of the symptoms. Due to the advantages in cancer diagnosis and treatments, survival rates of cancer patients rise and CIPN may occur even more frequently in the future. In this review, we summarize current recommendations of leading national and international societies regarding prevention and treatment options in CIPN. A special focus will be placed on current evidence for topical treatment of CIPN with high-dose capsaicin. Finally, an algorithm for CIPN treatment in clinical practice is provided, including both pharmacologic and non-pharmacologic modalities based on the clinical presentation.
Learn More >This study evaluated a battery of pain-stimulated, pain-depressed, and pain-independent behaviors for preclinical pharmacological assessment of candidate analgesics in mice. Intraperitoneal injection of dilute lactic acid (IP acid) served as an acute visceral noxious stimulus to produce four pain-related behaviors in male and female ICR mice: stimulation of (1) stretching and (2) facial grimace, and depression of (3) rearing and (4) nesting. Additionally, nesting and locomotion in the absence of the noxious stimulus were used to assess pain-independent drug effects. These six behaviors were used to compare effects of two mechanistically distinct but clinically-effective positive controls (ketoprofen and oxycodone), and two negative controls that are not clinically approved as analgesics but produce either general motor depression (diazepam) or motor stimulation (amphetamine). We predicted that analgesics would alleviate all IP acid effects at doses that did not alter pain-independent behaviors, whereas negative controls would not. Consistent with this prediction, ketoprofen (0.1-32 mg/kg) produced the expected analgesic profile, whereas oxycodone (0.32-3.2 mg/kg) alleviated all IP acid effects except depression of rearing at doses lower than those that altered pain-independent behaviors. For the negative controls, diazepam (1-10 mg/kg) failed to block IP acid-induced depression of either rearing or nesting, and only decreased IP acid-stimulated behaviors at doses that also decreased pain-independent behaviors. Amphetamine (0.32-3.2 mg/kg) alleviated all IP acid effects, but only at doses that also stimulated locomotion. These results support utility of this model as a framework to evaluate candidate-analgesic effects in a battery of complementary pain-stimulated, pain-depressed, and pain-independent behavioral endpoints. Preclinical assays of pain and analgesia often yield false-positive effects with candidate analgesics. This study used two positive-control analgesics (ketoprofen, oxycodone) and two active negative controls (diazepam, amphetamine) to validate a strategy for distinguishing analgesics from non-analgesics by profiling drug effects in a battery of complementary pain-stimulated, pain-depressed, and pain-independent behaviors in male and female mice.
Learn More >Enhanced signaling of the endocannabinoid system (eCB) through inhibition of the catabolic enzymes monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH) has received increasing interest for development of candidate analgesics. This study compared effects of MAGL and FAAH inhibitors with effects of ∆9-tetrahydrocannabinol (THC) using a battery of pain-stimulated, pain-depressed, and pain-independent behaviors in male and female mice. Intraperitoneal injection of dilute lactic acid (IP acid) served as an acute visceral noxious stimulus to stimulate two behaviors (stretching, facial grimace) and depress two behaviors (rearing, nesting). Nesting and locomotion were also assessed in the absence of IP acid as pain-independent behaviors. THC and a spectrum of six eCB catabolic enzyme inhibitors ranging from MAGL- to FAAH-selective were assessed for effectiveness to alleviate pain-related behaviors at doses that did not alter pain-independent behaviors. The MAGL-selective inhibitor MJN110 produced the most effective antinociceptive profile, with 1.0 mg/kg alleviating IP acid effects on stretching, grimace, and nesting without altering pain-independent behaviors. MJN110 effects on IP acid-depressed nesting had a slow onset and long duration (40min to 6hr), were blocked by rimonabant, and tended to be greater in females. As inhibitors increased in FAAH-selectivity, antinociceptive effectiveness decreased. PF3845, the most FAAH-selective inhibitor, produced no antinociception up to doses that disrupted locomotion. THC decreased IP acid-stimulated stretching and grimace at doses that did not alter pain-independent behaviors; however, it did not alleviate IP acid-induced depression of rearing or nesting. These results support further consideration of MAGL-selective as candidate analgesics for acute inflammatory pain. This study characterized a spectrum of endocannabinoid (eCB) catabolic enzyme inhibitors ranging in selectivity from monoacylglycerol lipase- (MAGL-) selective to fatty acid amide hydrolase- (FAAH-) selective in a battery of pain-stimulated, pain-depressed, and pain-independent behaviors previously pharmacologically characterized in a companion paper. This battery provides a method for prioritizing candidate analgesics by effectiveness to alleviate pain-related behaviors at doses that do not alter pain-independent behaviors, with inclusion of pain-depressed behaviors increasing translational validity and decreasing susceptibility to motor-depressant false positives.
Learn More >The analysis of brain signal variability is a promising approach to understand pathological brain function related to chronic pain. This study investigates whether blood-oxygen-level-dependent signal variability (BOLD) in specific frequency bands is altered in temporomandibular disorder (TMD) and correlated to its clinical features. Twelve patients with chronic myofascial TMD and 24 healthy controls (HCs) underwent resting-state functional magnetic resonance imaging. The BOLD was measured as the standard deviation of the BOLD time series at each voxel and compared between groups. We also examined the potential relationship between the BOLD and the catechol–methyltransferase () ValMet polymorphism. We assessed sensory-discriminative pain in the craniofacial region, pain sensitivity to sustained masseteric pain challenge, and TMD pain frequency for clinical correlation. Patients displayed reduced BOLD in the dorsolateral prefrontal cortex (dlPFC) as compared with HC in all frequency bands. In the slow-3 band, patients also showed reduced BOLD in the medial dorsal thalamus, primary motor cortex (M1), and primary somatosensory cortex (S1) and heightened BOLD in the temporal pole. Notably, we found a significant correlation between lower BOLD (slow-3) in the orofacial M1/S1 regions and higher clinical pain (intensity/area) and higher sensitivity of the masseter muscle pain. Moreover, lower BOLD (slow-3) in the dlPFC and ventrolateral PFC was associated with a higher TMD pain frequency. Participants who had the Met substitution exhibited lower BOLD in the dlPFC and higher BOLD in the temporal pole as compared with participants without the Met substitution. An increasing number of Met alleles was associated with lower dlPFC and greater temporal pole BOLD in both HC and TMD groups. Together, we demonstrated that chronic TMD patients exhibit aberrant BOLD in the top-down pain modulatory and sensorimotor circuits associated with their pain frequency and severity. ValMet polymorphism might affect clinical symptoms in association with regional brain signal variability, specifically involved in cognitive and emotional regulation of pain.
Learn More >Sensitization in office workers with chronic neck pain in different pain conditions and intensities.
Office workers with chronic neck pain demonstrates signs of widespread hyperalgesia, less efficient descending pain modulation, which could indicate sensitization of central pain pathways. No studies have assessed a wide variety of office workers with different chronic neck pain disorders and assessed the impact of pain intensity on assessments of central pain pathways. This study aimed to assessed pressure pain thresholds (PPTs), temporal summation of pain (TSP) and conditioned pain modulation (CPM) and to associate these with pain intensity and disability in subgroups of office workers.
Learn More >This pilot trial examined the effects of a combined intervention of mindfulness meditation followed by aerobic walking exercise compared with a control condition in chronic low back pain patients. We hypothesized that meditation before exercise would reduce disability, pain, and anxiety by increasing mindfulness prior to physical activity compared with an audiobook control group.
Learn More >Driving is one of the most widespread aspects of daily living to people in the United States and is an active process that requires various cognitive functions, such as attention. Chronic low back pain (CLBP) is one of the more prevalent and costly health conditions in the world, with individuals who report CLBP also reporting significant impairment across different domains of daily life both physically and cognitively. However, despite the prevalence of these two constructs, research detailing the experience of driving in pain remains largely underrepresented. This cross-sectional study sought to characterize the driving experience of people who experience CLBP, focusing on the psychological constructs related to chronic pain like pain catastrophizing, affective responses (irritability, anxiety, fear), and self-reported driving behaviors and outcomes.
Learn More >The A3 adenosine receptor (A3AR) has emerged as a therapeutic target with A3AR agonists to tackle the global challenge of neuropathic pain; investigation into their mode of action is essential for ongoing clinical development. A3ARs on immune cells, and their activation during pathology, modulates cytokine release. Thus, immune cells as a cellular substrate for the pharmacological action of A3AR agonists is enticing but unknown. Studies herein discovered that RagKO mice lacking T- and B-cells are insensitive to the anti-allodynic effects of A3AR agonists versus wild-type (WT) mice. Similar findings were observed in interleukin-10 and interleukin-10 receptor knockout mice. Adoptive transfer of CD4+ T-cells (CD4+-T) from WT mice infiltrated the dorsal root ganglion (DRG) and restored A3AR agonist-mediated anti-allodynia in RagKO mice; CD4+-T from Adora3KO or Il10KO mice did not. Transfer of CD4+-T from WT, but not Il10KO, into Il10KO mice fully reinstated anti-allodynic effects of A3AR activation. Transfer of CD4+-T from WT, but not Il10KO, into Adora3KO mice fully reinstated anti-allodynic effects of A3AR activation. Notably, A3AR agonism reduced DRG neuron excitability when co-cultured with CD4+-T in an IL-10-dependent manner. A3AR actions on CD4+-T infiltrate in the DRG decreased phosphorylation of GluN2B-containing N-methyl-D-aspartate receptors at Tyr1472, a modification associated with regulating neuronal hypersensitivity. Our findings establish that activation of A3AR on CD4+-T cells to release of IL-10 is required and sufficient for A3AR agonists as therapeutics.
Learn More >Chronic low back pain (CLBP) is often without clear underlying pathology. Affective disturbance and dysfunctional pain mechanisms, commonly observed in populations with CLBP, have, therefore, been suggested as potential contributors to CLBP development and maintenance. However, little consensus exists on how these features interact and if they can be targeted using non-invasive brain stimulation. In this pilot trial, 12 participants completed two phases (Active or Sham) of high-definition transcranial direct current stimulation (HD-tDCS) to the medial prefrontal cortex, applied for 20 min on three consecutive days. Clinical pain ratings, questionnaires, and sensitivity to painful cuff pressure were completed at baseline, then 4 trials of conditioned pain modulation (CPM; alone, with distraction using a Flanker task, with positive affect induction, and with negative affect induction using an image slideshow) were performed prior to HD-tDCS on Day 1 and Day 4 (24 h post-HD-tDCS). At baseline, attentional and affective manipulations were effective in inducing the desired state ( < 0.001) but did not significantly change the magnitude of CPM-effect. Active HD-tDCS was unable to significantly alter the magnitude of the shift in valence and arousal due to affective manipulations, nor did it alter the magnitude of CPM under any basal, attentional, or affective manipulation trial significantly on Day 4 compared to sham. The CPM-effect was greater across all manipulations on Day 1 than Day 4 ( < 0.02) but also showed poor reliability across days. Future work is needed to expand upon these findings and better understand how and if HD-tDCS can be used to enhance attentional and affective effects on pain modulation.
Learn More >Appropriate outcome measures and high-quality intervention trials are critical to advancing care for children with chronic pain. Our aim was to update a core outcome set for pediatric chronic pain interventions. The first phase involved collecting providers', patients', and parents' perspectives about treatment of pediatric chronic pain to understand clinically meaningful outcomes to be routinely measured. The second phase was to reach consensus of mandatory and optional outcome domains following the OMERACT framework. A Modified Delphi study with two rounds was conducted including three stakeholder groups: children with chronic pain (n=93), their parents (n=90), and health care providers who treat youth with chronic pain (n=52). Quantitative and qualitative data from Round 1 of the Delphi study were summarized to identify important outcomes, which were condensed to a list of 10 outcome domains. Round 2 surveys were analyzed to determine the importance of the 10 domains and their relative ranking in each stakeholder group. A virtual consensus conference was held with the Steering committee to reach consensus on a set of recommended outcome domains for pediatric chronic pain clinical trials. It was determined, by unanimous vote, that Pain Severity, Pain Interference with Daily Living, Overall Well-being, and Adverse Events, including Death, would be considered Mandatory domains to be assessed in all trials of any type of intervention. Emotional Functioning, Physical Functioning, and Sleep were Important but optional domains. Last, the research agenda identifies several important emerging areas, including biomarkers. Future work includes selecting appropriate validated measures to assess each outcome domain.
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