Does mutual compensation of the cognitive effects induced by pain and opioids exist? An experimental study

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.'.

Patient reported outcomes and neuropsychological testing in patients with chronic non-cancer pain in long-term opioid therapy: a pilot study

Background and aims Opioid consumption has increased dramatically in patients with chronic non-cancer pain (CNCP), but long-term consequences are still unclear. The aim of this study is to investigate the effects of long-term opioid treatment on pain, cognition, mood, sleep and quality of life in CNCP patients. Methods In this cross-sectional pilot study, two groups of patients with CNCP treated in a multidisciplinary pain center were selected: (1) opioid group: ≥30 mg morphine equivalent/day for >4 weeks, and (2) control group: no opioid consumption for >4 weeks. Socio-demographic data, alcohol consumption, smoking habits and body mass index (BMI) were registered and pain (brief pain inventory), mood (Hospital Anxiety and Depression Scale), sleep (Pittsburgh Sleep Quality Index) and quality of life (RAND 36-Item Health Survey) were assessed. Continuous Reaction Time and the Digit Span Test were used to evaluate cognitive function. Data was analyzed with a Fisher's exact test and Wilcoxon two-sample test. Results Forty-two patients with CNCP were included (21 in each group). No differences regarding socio-demographics, smoking/alcohol habits and duration, type, or intensity of pain were found. More patients in the opioid group had significantly higher BMI (62% above BMI 25 vs. 33.3%, p = 0.042). Consequently, the subsequent data analyses were controlled for BMI. The two groups did not differ in pain, cognition, anxiety, depression, sleep or quality of life but both showed lower values than the normal standards. Further, the opioid group presented a tendency to lower ratings regarding pain and social function and performed below the normal cut off in the continuous reaction time. Conclusions No significant differences between the two groups were found regarding any of the above-mentioned variables. Interestingly, the patients assessed, regardless of taking opioids or not, could be classified with moderate pain intensity, anxiety and low quality of sleep and life compared to norm standards. Implications The findings of this pilot study suggested that long-term opioid treatment may influence pain and quality of life among CNCP patients. A larger cohort is needed to verify these findings.

Effects of opioid/cannabinoid mixtures on impulsivity and memory in rhesus monkeys

The opioid epidemic underscores the need for safer and more effective treatments for pain. Combining opioid receptor agonists with drugs that relieve pain through nonopioid mechanisms could be a useful strategy for reducing the dose of opioid needed to treat pain, thereby reducing risks associated with opioids alone. Opioid/cannabinoid mixtures might be useful in this context; individually, opioids and cannabinoids have modest effects on cognition, and it is important to determine whether those effects occur with mixtures. Delay discounting and delayed matching-to-sample tasks were used to examine effects of the mu-opioid receptor agonist morphine (0.32-5.6 mg/kg), the cannabinoid CB1/CB2 receptor agonist CP55940 (0.0032-0.1 mg/kg), and morphine/CP55940 mixtures on impulsivity (n = 3) and memory (n = 4) in rhesus monkeys. Alone, each drug decreased rate of responding without modifying choice in the delay-discounting task, and morphine/CP55940 mixtures reduced choice of one pellet in a delay dependent manner, with monkeys instead choosing delayed delivery of the larger number of pellets. With the exception of one dose in one monkey, accuracy in the delayed matching-to-sample task was not altered by either drug alone. Morphine/CP55940 mixtures decreased accuracy in two monkeys, but the doses in the mixture were equal to or greater than doses that decreased accuracy or response rate with either drug alone. Rate-decreasing effects of morphine/CP55940 mixtures were additive. These data support the notion that opioid/cannabinoid mixtures that might be effective for treating pain do not have greater, and might have less, adverse effects compared with larger doses of each drug alone.

Effects of morphine/CP55940 mixtures on an impulsive choice task in rhesus monkeys

µ-Opioid receptor agonists are commonly used to treat pain despite their adverse effects. In preclinical studies, cannabinoid receptor agonists increase the potency of opioids for producing antinociceptive but not reinforcing effects. It is unknown whether other adverse effects of these drugs, such as impairment of complex behavior, are enhanced by their co-administration. This study characterized the effects of morphine (µ-opioid receptor agonist; 0.32-5.6 mg/kg, subcutaneously) and CP55940 (CB1/CB2 cannabinoid receptor agonist; 0.0032-0.32 mg/kg, subcutaneously), alone and in mixtures, in monkeys (n=3) choosing between one pellet delivered immediately and two pellets delivered after a delay. Two consecutive choices of the immediate or delayed reward decreased or increased, respectively, the delay. The median adjusted delay, indicating indifference between the immediate and delayed reinforcers, was increased by morphine (3.2 mg/kg) and CP55940 (0.01-0.032 mg/kg). Performance after administration of morphine (0.32 and 1 mg/kg)/CP55940 (0.0032-0.032 mg/kg) mixtures was not different from performance after CP55940 alone. Neither morphine, CP55940, nor mixtures decreased the median adjusted delay (i.e. increased impulsivity). These findings failed to confirm previous studies showing that morphine increases impulsivity, perhaps because of procedural differences among studies. Treatment of pain often requires repeated drug administration; thus, it remains to be determined whether the present findings predict the effects of chronically administered morphine/CP5540 mixtures on impulsive choice.

Does experimentally induced pain affect attention? A meta-analytical review

Background

Recent studies have found that clinical pain is related to cognitive impairment. However, there remains a scarcity of systematic reviews on the influence of acute pain on attention. Laboratory-induced pain is often used to simulate acute pain. The current systematic meta-analysis aimed to evaluate the effect of induced-pain on three components of attention (orienting, alerting, and executive attention) in healthy subjects.

Methods

A systematic search of three databases was performed. Only data from studies that administered laboratory-induced pain and that also included a control group were selected. The effects of experimental pain on orienting attention, alerting attention, and executive attention were analyzed. Two reviewers assessed the studies and extracted relevant data according to the Cochrane Collaboration and Preferred Reporting Items for Systematic Reviews and Meta-Analysis Guidelines.

Results

Eight studies were included in the meta-analysis. Orienting attention was marginally interrupted by pain under the invalid cue and marginally facilitated by pain under the valid cue condition. Performance on alerting attention was decreased by pain. Executive attention was not significantly affected by pain.

Conclusion

There was moderate evidence that experimentally induced pain can produce effects on orienting and alerting attention but not on executive attention. This meta-analysis suggests that experimentally induced pain influences some aspects of attention.

Effects of long-term opioid analgesics on cognitive performance and plasma cytokine concentrations in patients with chronic low back pain: a cross-sectional pilot study

INTRODUCTION

Cognitive performance and inflammation are altered in people with chronic low back pain (CLBP). Yet, the magnitude of these changes has been unclear because of the potential influence of opioid analgesics.

OBJECTIVES

This cross-sectional pilot study aimed to explore whether patients with CLBP receiving long-term opioid analgesics differed from patients not taking opioids on measures of cognitive performance and plasma cytokine concentrations.

METHODS

Patients with CLBP who were either taking (N = 18) or not taking (N = 22) opioids daily for 3 or more months were recruited from a tertiary care private hospital and compared with healthy adults (N = 20). All groups were administered validated questionnaires to assess depression, anxiety, and stress; a cognitive test of memory, attention, and executive function; and a peripheral blood draw to measure proinflammatory (IL-1β, IL-2, IL-8, IL-12p70, TNF-α, and IFN-γ), anti-inflammatory (IL-4, IL-10, and IL-13), and pleiotropic (IL-6) cytokine concentrations. Patients also completed pain-specific questionnaires.

RESULTS

Patients receiving opioid analgesics performed significantly (P < 0.05) worse in attention and had significantly (P < 0.05) lower pain self-efficacy beliefs than those patients not taking opioids. Patient groups did not differ in mean pain severity or pain interference scores, tests of memory and executive function, and mean plasma cytokine concentrations, despite long-term opioid analgesics.

CONCLUSION

Patients receiving long-term opioid analgesics for CLBP have minor differences when compared with patients not taking opioids. This has important clinical implications when considering long-term treatment for patients with CLBP.

Tapering off long-term opioid therapy in chronic non-cancer pain patients: A randomized clinical trial

BACKGROUND

The indications for initiating long-term opioid treatment (L-TOT) for chronic non-cancer pain (CNCP) are often unclear and associated with problematic use. This study aimed at evaluating the efficacy of stabilizing opioid therapy followed by a sequential opioid tapering off program in CNCP patients.

METHODS

A randomized clinical trial with a medications stabilization period (Phase 1) was followed by an opioid tapering off program (Phase 2). In Phase 2, patients were randomized to Control Group (stable treatment) or Taper off Group (sequential opioid dose reduction) and assessed at baseline, after stabilization and up to 6 months. Primary outcomes: measures of cognitive function; secondary outcomes: pain, sleep, rest, quality of life, depression, anxiety, opioid misuse and opioid withdrawal symptoms.

RESULTS

In all, 274 patients were screened; 75 were included, out of which 40 dropped out before Phase 2. Those who succeeded Phase 1 (n = 35) had weak/moderate improvements of psychomotor function (p = 0.020), sleeping hours (p = 0.031), opioid withdrawal symptoms (p = 0.019), measures of quality of life (p ≤ 0.043) and opioid misuse scores (p = 0.003). In Phase 2, patients in Taper off Group (n = 15) experienced stable pain intensity and felt significantly more rested at third assessment than the Control Group (n = 20).

CONCLUSIONS

The opioid tapering off program was not successful due to the vast number of dropouts. Phase 1 was associated with weak to moderate improvements on psychomotor function, sleeping, opioid withdrawal symptoms, quality of life and reduced risk of opioid misuse. In the intervention group of Phase 2, pain intensity was stable and patients felt more rested.

SIGNIFICANCE

This trial showed that sequential tapering off L-TOT in CNCP patients may be an unfeasible approach. However, improvements after opioid treatment stabilization were achieved and stable pain intensity in those tapered off may encourage the development of more refined programs.

Optimizing Cognitive Function in Persons With Chronic Pain

OBJECTIVES

Cognitive functioning is commonly disrupted in people living with chronic pain, yet it is an aspect of pain that is often not routinely assessed in pain management settings, and there is a paucity of research on treatments or strategies to alleviate the problem. The purpose of this review is to outline recent research on cognitive deficits seen in chronic pain, to give an overview of the mechanisms involved, advocate cognitive functioning as an important target for treatment in pain populations, and discuss ways in which it may be assessed and potentially remediated.

METHODS

A narrative review.

RESULTS

There are several options for remediation, including compensatory, restorative, and neuromodulatory approaches to directly modify cognitive functioning, as well as physical, psychological, and medication optimization methods to target secondary factors (mood, sleep, and medications) that may interfere with cognition.

DISCUSSION

We highlight the potential to enhance cognitive functions and identify the major gaps in the research literature.