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8 Articles in this Series
Introduction
Bench to Bedside: Clinical Tips From APS Poster Presentations
New Pain Research Underscores the Importance of Sufficient Rest
The Benefits of Exercise for Pain Management
Exercise as Postoperative Analgesic?
How Race Affects Pain
Increased Centralized Pain in African American Patients
Managing Post-Tonsillectomy Pain in Obese Children
Research Offers Insight Into Fibromyalgia and Pain

New Pain Research Underscores the Importance of Sufficient Rest

Although it's been well established that sleep influences pain, new research presented at the annual American Pain Society meeting last month further explored the topic along with a review of new sleep measurement tools and an investigation into genetic correlations. Here, a roundup of three new studies.

Knee Osteoarthritis Patients Suffer from Centralized Pain and Loss of Sleep

Patients living with knee osteoarthritis (KOA) can show signs of central sensitization (CS),1 a hyper-excitability to nociception that can not only bolster pain severity but also influence the reliance on analgesics and reduce satisfaction reported after surgery.2 But there may be another significant factor at play with KOA patients—how well they sleep.

A team of researchers led by Michael T. Smith, PhD, founder of the Behavioral Sleep Medicine Program at Johns Hopkins School of Medicine, Baltimore, presented the results of two studies on the relationship between sleep, pain, and CS, including a recent study conducted on KOA patients with and without insomnia.

Regardless of sex or race, patients who suffered from sleep fragmentation appeared to show a stronger correlation between CS and clinical pain, noted Dr. Smith, professor in the School of Medicine, Department of Psychiatry and Behavioral Sciences. This finding further underscores the importance of recognizing sleep as an important clinical factor in KOA patients with clinical pain and CS.

"Clinical pain and CS are overlapping conditions and are believed to also have a bidirectional relationship,” and while the relationship between these two facets has become a burgeoning topic of research, there have been few studies about the possible interactions between clinical pain, sleep, and CS, noted Dr. Smith and colleagues in their poster. 3

This recent work suggests that improving sleep may be associated with a reduction in pain.

In the study, the researchers included 139 KOA patients (72% female; mean age = 61yr). Each participant completed daily diaries for 2 weeks to log sleep and clinical pain experiences. The patients were also given an extensive quantitative sensory testing procedure to establish their CS index.

Researchers looked at wake after sleep onset time (WASO), which would indicate sleep fragmentation and one of the most common sleep complaint among KOA patients.

After analyzing the patients’ symptom diaries, the researchers found sleep fragmentation partially mediated the relationship between CS and pain that patients experienced (total effect, P < 0.001; direct and indirect effects, P < 0.001), regardless of their gender or racial background—variables that have been known to affect both pain and sleep.

Various studies have explored the effects of sleep deprivation on nociceptive processing,4 and these recent findings further underscore the importance of recognizing sleep as an important variable for patients with chronic pain and treating the the problem as an significant component in the process.

Disrupted Sleep: Measurable and Significant to Pain Outcomes

It’s been suggested that patients with chronic pain will develop maladaptive sleeping habits in order to cope with the frequent pain they experience. These compromised sleeping patterns may not only further perpetuate the insomnia but could also influence the pain they experience up to a year following surgical intervention.

In the second study presented by  Johns Hopkins researchers,5 the team presented data from a novel Sleep and Pain Behaviors Survey (SPBS) they developed in order to measure sleep behaviors specific to pain. The survey assessed three aspects:

  1. Having to lay down and rest during the day because of pain
  2. Spending ≥ 2 hours a day in the bedroom because of pain
  3. Taking extra narcotics to get to sleep

Fifty-seven patients with KOA (44% male; mean age= 65 yr), who were scheduled to undergo a total knee replacement (TKR) surgery, completed the survey and contributed baseline self-report measures of insomnia (Insomnia Severity Index [ISI]) and KOA-specific Western Ontario and McMaster Universities Arthritis Index (WOMAC) and nonspecific Brief Pain Inventory (BPI) measurements for clinical pain. Researchers managed to get a portion of the patient cohort to resubmit these measurements at 6 weeks (n = 32), 3 months (n = 23), and 6 months (n = 21) postsurgery.

The SPBS appeared to be a useful tool, showing internal reliability at baseline (Cronbach's α = .775) and re-test reliability at 3 months (r = .878; P < 0.001) and 6 months after the surgery (r = .830; P < 0.001). Baseline SPBS scores showed strong association with the ISI, BPI, and WOMAC at baseline and at every follow-up time point (P ≤ 0.03).

The researchers also were able to readminister the ISI and clinical pain measures a year after the surgery to 20 patients. Even after controlling for age, baseline ISI, and baseline pain, the baseline SPBS scores predicted BPI severity (P = 0.008), BPI interference (P < 0.001), and WOMAC scores (P < 0.001) a year after surgery. Given the success of the SPBS as a measurement tool, pain-related sleep behavior could be another significant, modifiable factor that contributes to patients’ pain outcomes following a TKR procedure, concluded Dr. Smith and colleagues.

Pain, Depression and Sleep Deprivation. Is There a Genetic Link?

Understanding how loss of sleep interacts with pain experience in patient outcomes is a chief concern to practitioners. However, a third factor is also well-known to interact with pain and sleep—depression. The relationship between the trifecta of insomnia, pain, and depression may have a genetic etiology that researchers are just beginning to understand.

In the third study, researchers from the University of California at San Diego led by Niloofar Afari, PhD, used standard biometric methods to analyze 400 twins, taken from a community sample provided by the University of Washington Twin Registry. The twins completed a series of standardized self-report questionnaires and biometric modeling.6

The researchers wanted to assess whether pain, sleep dysfunction, and depression phenotypes shared a common genetic diathesis. After decomposing correlations among the various phenotypes, the researchers determined the percentage of heritability present for pain symptoms, depression symptoms, and sleep dysfunction, at 25% (95% CI: 9, 41%), 39% (CI: 22, 53%), and 37% (CI: 20, 51%), respectively. The rest of the variance related to non-shared environmental influences.

The researchers found noticeable genetic correlations amongst the phenotypes:

  • Pain and sleep dysfunction genetic correlation: rg = .69 (CI: .33, .97)
  • Pain and depression symptoms genetic correlation: rg = .56 (CI = .34, .98)
  • Depression symptoms and sleep dysfunction genetic correlation : rg = .61 (CI: .44, .88)

“Our results indicate that the link between pain, sleep, and depression symptoms is primarily explained by shared genetic influences. Furthermore, the genetic factors for sleep and pain are highly correlated even when accounting for depression,” noted Dr. Afari and colleagues, perhaps a sign that a specific genetic etiologic link does exist between pain and sleep dysfunction.

References

  1. Fingleton C, Smart K, Moloney N, et al. Pain sensitization in people with knee osteoarthritis: a systematic review and meta-analysis. Osteoarthritis Cartilage. 2015;23(7):1043-1056.
  2. Kim SH, Yoon KB, Yoon DM, et al. Influence of centrally mediated symptoms on postoperative pain in osteoarthritis patients undergoing total knee arthroplasty: A prospective observational evaluation. Pain Pract. 2015;5(6):E46-53.
  3. Burton E, Campbell C, Robinson M, et al. (2016, April). Sleep mediates the relationship between central sensitization and clinical pain. Poster presented at: annual meeting of the American Pain Society; May 11-14, 2016; Austin, TX. Poster 322.
  4. Matre D, Hu L, Viken LA, et al. Experimental sleep restriction facilitates pain and electrically induced cortical responses. Sleep. 2015; 38(10):1607-1617.
  5. Richards J, Pejsa M, Hand M, et al. Psychometric evaluation and predictive validity of the sleep and pain behaviors survey in knee osteoarthritis patients undergoing total knee replacement. Poster presented at: annual meeting of the American Pain Society; May 11-14, 2016; Austin, TX. Poster 166.
  6. Gasperi M, Herbert M, Schur E, et al. Genetic and environment influences on pain, sleep, and depression symptoms in a community sample of twins. Poster  presented at: annual meeting of the American Pain Society; May 11-14, 2016; Austin, TX. Poster 201.
Next summary: The Benefits of Exercise for Pain Management
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