Sleep deficiency and chronic pain: potential underlying mechanisms and clinical implications

The Glymphatic System and Pain

The glymphatic system is network of perivascular spaces through which cerebrospinal fluid and interstitial fluid can move through the brain, clearing metabolic waste, such as amyloid beta, lactate and more, from the parenchyma. This cleaning system is regulated by sleep and norepinephrine, with increased levels of norepinephrine during wakefulness inhibiting fluid movement. Norepinephrine is also essential for transition from acute to chronic pain, and sufferers of chronic neuropathic pain frequently present with sleep disruption. These connections among glymphatic clearance, sleep, and pain are very intriguing, and might lead to nonpharmaceutical interventions for pain treatment. This short perspective provides a rationale for the hypothesis that mind-body interventions-such as acupuncture-can reduce norepinephrine and increase glymphatic function, ultimately relieving chronic neuropathic pain.

Sleep Disturbance and Its Association with Pain Severity and Multisite Pain: A Prospective 10.7-Year Study

INTRODUCTION

Sleep disturbance is often comorbid with chronic pain disorders, with emerging evidence suggesting a stronger effect of sleep disturbance on pain than vice versa; however, few studies have evaluated the long-term associations between sleep disturbance and pain. This study was to examine the associations of sleep disturbance with knee pain severity, number of painful sites (NPS) and persistent pain in a 10.7-year cohort study.

METHODS

A total of 1099 community-dwelling older adults (age mean ± SD, 63 ± 7.5 years; 51% female) were recruited and followed up at 2.6, 5.1 and 10.7 years later. Data on demographics, body mass index, physical activity and comorbidities were collected. At each time point, sleep disturbance, knee pain severity and NPS were assessed by using questionnaires. Multisite pain (MSP) was defined as NPS ≥ 2. Persistent knee pain or MSP was defined as having knee pain or MSP at all time points, respectively. Multivariable mixed-effects models and log-binomial regression were applied.

RESULTS

In multivariable analyses, sleep disturbance was associated with greater knee pain severity (β 0.91/unit, 95% CI 0.70-1.11) and more NPS [(relative risk (RR) 1.10/unit, 95% CI 1.07-1.14] in a dose-response manner. Persistent sleep disturbance was associated with persistent knee pain (RR 1.90, 1.26-2.87) and MSP (RR 1.29, 1.07-1.56). Persistent knee pain and MSP were also associated with persistent sleep disturbance (knee pain: RR = 1.99; MSP: RR = 2.71, both P < 0.05).

CONCLUSIONS

Sleep disturbance was independently associated with greater pain severity and NPS in a dose-response manner. A reciprocal relationship between persistent sleep disturbance and persistent pain suggests treating either problem could help the other.

High levels of preoperative pain and fatigue are red flags for moderate-severe pain 12 months after total knee arthroplasty-A longitudinal cohort study

Background

Moderate/severe pain after total knee arthroplasty (TKA) is a poor surgical outcome. Many studies have identified preoperative risk factors of pain after TKA, but studies of the joint contributions of co‐occurring symptoms are lacking.

Methods

Patients undergoing primary TKA (n = 202) were enrolled in a longitudinal cohort study. Preoperatively, patients completed questionnaires measuring demographics and symptoms (pain, fatigue, sleep problems and depression). Pain was re‐assessed 12 months after TKA. Logistic regression analysis was used to compute the probabilities of moderate‐severe pain at 12 months based on preoperative symptom levels, and results were combined into a risk matrix.

Results

More than one‐third (40%) of patients (n = 187) reported moderate‐severe pain after TKA. Among preoperative risk factors included in the logistic regression analyses were age, sex, pain, fatigue, sleep problems and depression. Adjusting for possible confounders, fatigue (p = 0.02) and pain (p = 0.01) were significant risk factors for moderate‐severe pain at 12‐months follow‐up and were retained in the final risk matrix. The co‐occurrence of high‐preoperative fatigue and pain scores resulted in 57% estimated probability of moderate‐severe pain at 12 months. Similarly, the co‐occurrence of low‐preoperative fatigue and pain scores resulted in 14% estimated probability of moderate‐severe pain 12 months after TKA.

Conclusion

The combination of high fatigue and pain scores prior to surgery was a key risk factor for moderate‐severe pain 12 months after TKA. Mapping of these factors could be used preoperatively to identify patients who are at risk to experience a poor outcome of TKA.

Electroacupuncture: A New Approach for Improved Postoperative Sleep Quality After General Anesthesia

General anesthesia produces a state of drug-induced unconsciousness that is controlled by the extent and duration of administered agents. Whether inhalation or intravenous in formulation, such agents may interfere with normal sleep-wake cycles, impairing postoperative sleep quality and creating complications. Electroacupuncture is a new approach widely applied in clinical practice during recent years. This particular technology helps regulate neurotransmitter concentrations in the brain, lowering norepinephrine and dopamine levels to improve sleep quality. It also alleviates surgical pain that degrades postoperative sleep quality after general anesthesia by downregulating immune activity (SP, NK-1, and COX-1) and upregulating serotonin receptor (5-HT1AR, 5-HT2AR) and endocannabinoid expression levels. However, large-scale, multicenter studies are still needed to determine the optimal duration, frequency, and timing of electroacupuncture for such use.

Exposure to greenspaces could reduce the high global burden of pain

Painful conditions are among the leading causes of years lived with disability, and may increase following the coronavirus pandemic, which has led to temporary closure of some healthcare services for people with chronic pain. To reduce this burden, novel, cost-effective and accessible interventions are required. We propose that greenspace exposure may be one such intervention. Drawing on evidence from neuroscience, physiology, microbiology, and psychology, we articulate how and why exposure to greenspaces could improve pain outcomes and reduce the high global burden of pain. Greenspace exposure potentially provides opportunities to benefit from known or proposed health-enhancing components of nature, such as environmental microbiomes, phytoncides, negative air ions, sunlight, and the sights and sounds of nature itself. We review the established and potential links between these specific exposures and pain outcomes. While further research is required to determine possible causal links between greenspace exposure and pain outcomes, we suggest that there is already sufficient evidence to help reduce the global burden of pain by improving access and exposure to quality greenspaces.

Relationships Between Psychological, Sleep, and Physical Activity Measures and Somatosensory Function in People With Peripheral Joint Pain: A Systematic Review and Meta-Analysis

OBJECTIVE

Alteration in somatosensory function has been linked to pain experience in individuals with joint pain. In this systematic review we aimed to establish the level of evidence of associations between psychological, social, physical activity, and sleep measures and somatosensory function that were assessed via quantitative sensory testing (QST) among individuals with joint pain.

METHODS

A comprehensive literature search was conducted in 6 electronic databases from their inception to July 2019. Two reviewers independently assessed the methodological quality using a modified Quality in Prognostic Studies (QUIPS) tool and supplemented with recommendations from the Critical Appraisal and Data Extraction for Systematic Review of Prediction Modelling Studies (CHARMS) checklist and the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool. The level of evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) system. Data were pooled to evaluate the strength of the relationships of interest.

RESULTS

Seventeen studies related to joint pain were included. Pain catastrophizing, depression, anxiety, and physical activity level have been shown to have a significant (small to fair) association with several QST measures. Pressure pain threshold (PPT) is the only measure that was found to be consistently correlated with all the domains. The overall quality of evidence for all factors ranged from very low to moderate. Subgroup analysis revealed a stronger association for depression and pain catastrophizing and PPT and temporal pain summation in individuals with shoulder pain.

CONCLUSION

Psychological factors and physical activity levels are associated with somatosensory function in people with joint pain. These factors need to be adjusted when establishing predictive relationships between somatosensory function and pain outcomes in individuals with joint pain.

Sleep Disturbances After General Anesthesia: Current Perspectives

The purpose of this article is to review (1) sleep mechanism under general anesthesia, harmful effects of postoperative sleep disturbances; (2) risk factors associated with postoperative sleep disturbances; (3) measures to prevent and improve postoperative sleep disturbances. General anesthesia changes the postoperative sleep structure especially in elderly patients after major surgery and results in a high incidence rate of sleep disturbances. Sleep disturbances produce harmful effects on postoperative patients and lead to a higher risk of delirium, more cardiovascular events, and poorer recovery. Some researchers do propose non-pharmacological treatments such as attention to environmental and psychological factors, application of electroacupuncture (EA) technology and pharmacological treatments are helpful, but larger high-quality clinical trials with longer following-up are needed to further investigate the efficacy and safety.

A Brief Music App to Address Pain in the Emergency Department: Prospective Study

Background

Emergency physicians face the challenge of relieving acute pain daily. While opioids are a potent treatment for pain, the opioid epidemic has ignited a search for nonopioid analgesic alternatives that may decrease the dose or duration of opioid exposure. While behavioral therapies and complementary medicine are effective, they are difficult to deploy in the emergency department. Music is a potential adjunctive therapy that has demonstrated effectiveness in managing pain.

Objective

Our objective was to understand the feasibility and potential for an effect of a novel music app to address acute pain and anxiety in patients admitted to an emergency department observation unit.

Methods

This prospective cohort study enrolled patients admitted to an emergency department observation unit with pain who had received orders for opioids. We gathered baseline pain and psychosocial characteristics including anxiety, sleep disturbance, and pain catastrophizing using validated questionnaires. Participants received a smartphone-based music intervention and listened to the music in either a supervised (research assistant–delivered music session 3 times during their stay) or unsupervised manner (music used ad lib by participant). The app collected premusic and postmusic pain and anxiety scores, and participants provided qualitative feedback regarding acceptability of operating the music intervention.

Results

We enrolled 81 participants and randomly assigned 38 to an unsupervised and 43 to a supervised group. Mean pain in both groups was 6.1 (1.8) out of a possible score of 10. A total of 43 (53%) reported previous use of music apps at home. We observed an overall modest but significant decrease in pain (mean difference –0.81, 95% CI –0.45 to –1.16) and anxiety (mean difference –0.72, 95% CI –0.33 to –1.12) after music sessions. Reduction of pain and anxiety varied substantially among participants. Individuals with higher baseline pain, catastrophizing (about pain), or anxiety reported greater relief. Changes in pain were correlated to changes in anxiety (Pearson ρ=0.3, P=.02) but did not vary between supervised and unsupervised groups. Upon conclusion of the study, 46/62 (74%) reported they liked the music intervention, 57/62 (92%) reported the app was easy to use, and 49/62 (79%) reported they would be willing to use the music intervention at home.

Conclusions

A smartphone-based music intervention decreased pain and anxiety among patients in an emergency department observation unit, with no difference between supervised and unsupervised use. Individuals reporting the greatest reduction in pain after music sessions included those scoring highest on baseline assessment of catastrophic thinking, suggesting there may be specific patient populations that may benefit more from using music as an analgesic adjunct in the emergency department. Qualitative feedback suggested that this intervention was feasible and acceptable by emergency department patients.

Phase II double-blind randomised controlled trial of exogenous administration of melatonin in chronic pain (DREAM-CP): a study protocol

INTRODUCTION

Chronic pain is prevalent, and approximately half of patients with chronic pain experience sleep disturbance. Exogenous melatonin is licensed to treat primary insomnia and there is some evidence for analgesic effects of melatonin.The aim of this study is to investigate the effects of oral melatonin (as Circadin) 2 mg at night in adults with severe non-malignant pain of at least 3 months' duration.

METHODS AND ANALYSIS

We will conduct a randomised double-blind placebo-controlled cross-over study. The primary outcome is sleep disturbance. Secondary outcomes are pain intensity, actigraphy, fatigue, reaction time testing, serum melatonin and endogenous opioid peptide levels along with patient views about study participation.We aim to recruit 60 patients with severe chronic pain (average pain intensity ≥7 on the Brief Pain Inventory (BPI)) from a tertiary referral pain clinic in Northeast Scotland. Participants will be randomised to receive melatonin (as modified release Circadin) 2 mg daily for 6 weeks or placebo, followed by a 4-week washout period, then 6 weeks treatment with the treatment they did not receive. Participants will complete the Verran Snyder-Halpern Sleep Scale, Pittsburgh Sleep Quality Index, Pain and Sleep Questionnaire 3-item index, BPI and psychomotor vigilance reaction time testing at 6 points over 20 weeks. Actigraphy watches will be used to provide objective measures of sleep duration and latency and other sleep measures and will prompt patients to report contemporaneous pain and fatigue scores daily.Cross-over analyses will include tests for effects of treatment, period, treatment-period interaction (carryover effect) and sequence. Within-patient effects and longitudinal data will be analysed using mixed linear models, accounting for potential confounders.

ETHICS AND DISSEMINATION

Approved by Office for Research Ethics Committees Northern Ireland, reference 19/NI/0007. Results will be published in peer-reviewed journals and will be presented at national and international conferences.

TRIAL REGISTRATION NUMBER

ISRCTN12861060.

Cross-lagged longitudinal analysis of pain intensity and sleep disturbance

BACKGROUND

There is substantial evidence that pain intensity and sleep are related, with findings generally suggesting more support for the influence of sleep on pain intensity than vice versa. However, the strength and direction of the relationship has been found to vary among different populations, with few studies in individuals with chronic physical disabilities.

OBJECTIVE

Examine the directionality of the sleep and pain relationship in individuals with chronic physical disabilities.

METHODS

Cross-lagged effects models were generated using data from a longitudinal observational survey study of individuals (N = 1660) with multiple sclerosis (MS), muscular dystrophy (MD), post-polio syndrome (PPS), and spinal cord injury (SCI). Models evaluated the correlational effects of sleep disturbance and pain intensity, as well as the cross-lagged effects of sleep disturbance to pain intensity and vice versa.

RESULTS

The effects of pain on sleep were stronger than sleep on pain, although the magnitude of the effects were both relatively weak. Analyses within individual samples were consistent with the overall sample results for MS, MD, and PPS. In the SCI sample the magnitude and direction of the cross-lagged model paths were more variable than in the other samples.

CONCLUSIONS

The relationship between pain intensity and sleep disturbance appears bi-directional, but the effects are small in a sample of individuals with long-term disabilities. The temporal effects of pain on sleep disturbance appear stronger than the effects of sleep disturbance on pain intensity. Future research is needed to better understand this relationship in the context of pain and/or sleep disturbance treatments.

Poor Sleep Is a Risk Factor for Low-Back Pain among Healthcare Workers: Prospective Cohort Study

This study aimed to investigate the association between poor sleep and risk of low-back pain (LBP) in healthcare workers. Using a prospective cohort design with 1-year follow-up, a total of 1955 healthcare workers (60% nurses) from 389 departments at 19 hospitals responded to questionnaires containing items related to lifestyle, health, and working environment. Associations between sleep scores (0-100) at baseline and LBP intensity (0-10) at follow-up were modelled using cumulative logistic regression accounting for clustering at the department level and adjusted for lifestyle and psychosocial confounders. In the full population of healthcare workers, 43.9% and 24.4% experienced moderate and poor sleep, respectively. In the fully adjusted model with good sleep as reference, moderate, and poor sleep increased the risk of LBP at follow-up, with odds ratios (OR's) of 1.66 (95% confidence interval (CI) 1.35-2.04) and 2.05 (95% CI 1.57-2.69), respectively. Three sensitivity analyses including healthcare workers free from LBP, nurses, and nurses free from LBP at baseline, respectively, yielded similar results. In conclusion, poor sleep constitutes a potent risk factor for LBP among healthcare workers. The presented results provide strong incentives to evaluate and weigh current prevention policies against an updated biopsychosocial framework.

Number of Chronic Nighttime Insomnia Symptoms and Risk of Chronic Widespread Pain and Pain-Related Disability: The HUNT Study

STUDY OBJECTIVES

To examine the association between the number of chronic nighttime insomnia symptoms and the risk of chronic widespread pain (CWP) and pain-related disability.

METHODS

A prospective study of 10,847 participants in the Norwegian HUNT Study without chronic musculoskeletal pain at baseline in 2006-2008. We used a modified Poisson regression model to estimate adjusted risk ratios (RRs) with a 95% confidence interval (CI) for CWP and pain-related disability at follow-up in 2017-2019 associated with insomnia and number of nighttime insomnia symptoms at baseline. Chronic insomnia was defined according to the current classification system and grouped into three categories based on the number of reported nighttime symptoms (ie, difficulty initiating sleep, trouble maintaining sleep and early morning awakenings).

RESULTS

Compared to the reference group of people without insomnia, people with insomnia had RRs for CWP and pain-related disability of 1.64 (1.26-2.14) and 1.63 (1.37-1.94), respectively. When people with insomnia were categorized based on the number of nighttime symptoms, people who reported one, two, or three nighttime symptoms had RRs of CWP of 1.19 (95% CI 0.80-1.78), 1.78 (95 CI 1.13-2.80) and 3.08 (95% CI 1.93-4.92), respectively, compared to people without insomnia. The corresponding RRs for pain-related disability were 1.49 (95% CI 1.17-1.89), 1.46 (95% CI 2.04-2.05), and 2.46 (95% CI 1.76-3.42).

CONCLUSION

These findings indicate that people with insomnia characterized by symptoms in all phases of the sleep period have a substantially increased risk of CWP and pain-related disability.