Nociceptive input after peripheral nerve injury results in cognitive impairment and alterations in primary afferent physiology in rats

Developmental Mechanisms of CPSP: Clinical Observations and Translational Laboratory Evaluations

Understanding mechanisms that underly the transition from acute to chronic pain and identifying potential targets for preventing or minimizing this progression have specific relevance for chronic postsurgical pain (CPSP). Though it is clear that multiple psychosocial, family, and environmental factors may influence CPSP, this review will focus on parallels between clinical observations and translational laboratory studies investigating the acute and long-term effects of surgical injury on nociceptive pathways. This includes data related to alterations in sensitivity at different points along nociceptive pathways from the periphery to the brain; age- and sex-dependent mechanisms underlying the transition from acute to persistent pain; potential targets for preventive interventions; and the impact of prior surgical injury. Ongoing preclinical studies evaluating age- and sex-dependent mechanisms will also inform comparative efficacy and preclinical safety assessments of potential preventive pharmacological interventions aimed at reducing the risk of CPSP. In future clinical studies, more detailed and longitudinal peri-operative phenotyping with patient- and parent-reported chronic pain core outcomes, alongside more specialized evaluations of somatosensory function, modulation, and circuitry, may enhance understanding of individual variability in postsurgical pain trajectories and improve recognition and management of CPSP.

Factors mediating pain-related risk for opioid use disorder

Pain is a complex experience with far-reaching organismal influences ranging from biological factors to those that are psychological and social. Such influences can serve as pain-related risk factors that represent susceptibilities to opioid use disorder. This review evaluates various pain-related risk factors to form a consensus on those that facilitate opioid abuse. Epidemiological findings represent a high degree of co-occurrence between chronic pain and opioid use disorder that is, in part, driven by an increase in the availability of opioid analgesics and the diversion of their use in a non-medical context. Brain imaging studies in individuals with chronic pain that use/abuse opioids suggest abuse-related mechanisms that are rooted within mesocorticolimbic processing. Preclinical studies suggest that pain states have a limited impact on increasing the rewarding effects of opioids. Indeed, many findings indicate a reduction in the rewarding and reinforcing effects of opioids during pain states. An increase in opioid use may be facilitated by an increase in the availability of opioids and a decrease in access to non-opioid reinforcers that require mobility or social interaction. Moreover, chronic pain and substance abuse conditions are known to impair cognitive function, resulting in deficits in attention and decision making that may promote opioid abuse. A better understanding of pain-related risk factors can improve our knowledge in the development of OUD in persons with pain conditions and can help identify appropriate treatment strategies. This article is part of the special issue on 'Vulnerabilities to Substance Abuse.'.

Comparing objective cognitive impairments in patients with peripheral neuropathic pain or fibromyalgia

Existing studies on cognitive impairments in chronic pain do not investigate peripheral neuropathic pain (PNP) or compare pain conditions in a satisfactory manner. Here we aimed to compare executive dysfunctions in PNP patients with fibromyalgia (FM) and healthy controls (HC). Patients who self-reported cognitive impairments were assessed according to criteria for PNP or FM. Seventy-three patients met criteria and completed testing on executive functioning and IQ measures. We also included twenty matched healthy controls. Regression models controlling for age, sex and IQ, tested associations between group category (PNP, FM or HC) and outcomes. If a substantial association was detected, we followed up with head-to-head comparisons between PNP and FM. Multivariate regression models then tested associations between executive functioning and pain type, controlling for significant confounders. Results from head-to-head comparison between pain conditions showed significant differences on years lived with pain (FM > PNP), the use of anticonvulsants (PNP > FM) and use of analgesics (PNP > FM). When controlled for all significant differences, PNP patients had significantly lower scores on an attention-demanding cued-recall task compared to FM. Poor performance on attention-demanding cued-recall task was associated with PNP, which translate into problems with retaining fast-pace or advanced information.