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September 2017
David Craig, PharmD | Editor

Summaries

The Journal of Pain

Highlights from The Journal of Pain (Volume 18, No. 9, September 2017 Issue)

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Characteristics and Factors Associated with Pain in Older Homeless Individuals

Stephen W. Hwang, Emma Wilkins, Catharine Chambers, Eileen Estrabillo, Jon Berends, and Anna MacDonald; Centre for Research on Inner City Health, The Keenan Research Centre in the Li Ka Shing Knowledge Institute of St. Michael's Hospital, Toronto, Canada; Division of General Internal Medicine, Department of Medicine, University of Toronto, Toronto, Canada

Almost half of older adults experiencing homelessness report having longstanding chronic pain, mostly associated with post-traumatic stress syndrome, arthritis, and physical abuse, according to research reported in The Journal of Pain.

Researchers from the University of California San Francisco and San Francisco General Hospital studied 350 homeless adults age 50 years and older from overnight centers, homeless encampments, and meal programs in Oakland. They conducted study interviews at a community-based center that provided social services.

The research was designed to describe the severity and duration of pain and its association with demographic and clinical characteristics. Very little was known about these issues prior to this study. People who are homeless experience challenging physical environments, exposure to the elements, crowded shelters, and violence. Because all of these factors could contribute to the presence or severity of pain, the authors hypothesized that homeless adults in the sample would report a high prevalence of moderate to severe chronic pain. They also explored several factors that could be associated with chronic pain in this population.

The median age for homeless adults is approximately 50 years, and they have an earlier onset of age-related problems, such as functional and cognitive impairments, than the general population. More than 500,000 people are homeless in the United States at any time and more than 3 million experience homelessness in a given year.

Results of the study showed that almost half of the homeless adults interviewed said they had moderate to severe chronic pain, and three out of four of them said their pain had lasted 5 years or longer. Consistent with previous research, the study showed chronic pain was linked with a history of being victims, violence, having arthritis, and PTSD symptoms. However, there was no association between chronic pain and substance abuse, depression, or chronic medical conditions other than arthritis.

The authors noted the study provides the first estimates of chronic pain in a high-risk but poorly understood population. They concluded that the high prevalence of chronic pain in homeless adults age 50 years and older will require public health interventions that address pain and mental health problems in this growing population.

Sleep Quality, Affect, Pain, and Disability in Children with Chronic Pain: Is Affect a Mediator or Moderator?

Subhadra Evans, Vesna Djilas, Laura C. Seidman, Lonnie K. Zeltzer, Jennie C.I. Tsao; School of Psychology, Deakin University, Geelong, Australia; School of Psychology, Deakin University, Geelong, Australia; UCLA Pediatric Pain and Palliative Care Program, David Geffen School of Medicine at University of California, Los Angeles, CA

Little is known about the relationship between sleep, pain, and affect in children. Some studies have shown a reciprocal relationship with increased pain contributing to poor sleep quality and vice versa. However, new research suggests that sleep disruptions predict pain and functional disability with greater magnitude than pain predicts sleep problems.

Researchers from Deakin University in Australia and UCLA’s David Geffen School of Medicine sought to examine the relationship between children’s sleep quality in relation to pain intensity and functional disability and to assess the mediating and moderating roles of positive and negative affect. They hypothesized that the relationships between poor sleep and increased functional disability would be mediated by lower positive affect such that poor sleep quality would affect increased pain and disability at least partially through a reduction in the child’s positive mood.

The sample was part of an ongoing study examining pain, psychological health, and sociodemographic factors in a pediatric tertiary pain clinic. Two hundred thirteen children and adolescents were evaluated.

Results showed that 74 percent of study subjects reported disordered sleep, and poor sleep quality was significantly associated with increased, pain, disability, negative affect, and decreased positive affect. The authors concluded their hypothesis was partially supported. Negative affect mediated the relationship between poor sleep and increased functional disability. There was no evidence for affect as a moderator.

The study adds to the growing literature demonstrating the effect of poor sleep quality on children’s pain and functioning.


PAIN

Highlights from PAIN (Volume 158, No. 9, September 2017 Issue)

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Short-Duration Physical Activity Prevents the Development of Activity-Induced Hyperalgesia Through Opioid and Serotoninergic Mechanisms

Lucas V. Lima, Josimari M. DeSantana, Lynn A. Rasmussen, Kathleen A. Sluka; Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, IA; Graduate Program in Health Sciences, Federal University of Sergipe, Aracaju/Se, Brazil; Department of Physical Therapy, Federal University of Sergipe, Aracaju/Se

Although exercise is an important component in managing musculoskeletal pain conditions, it can enhance pain and hyperalgesia in chronic musculoskeletal pain conditions in humans and animals. The nucleus raphe magnus (NRM), nucleus raphe obscurus (NRO), and nucleus raphe pallidus (NRP), part of the rostral ventromedial medulla (RVM), not only inhibit and facilitate nociceptive behaviors but also modulate motor responses and may be involved in modulating effects of activity on nociception.

Regarding the NRM, NRP, and NRO, this group of investigators previously showed increased phosphorylation of the NR1 subunit of the N-methyl-D-aspartate receptor (p-NR1) in models of muscle pain, neuron activation by an acute bout of exercise, and increases in the serotonin transporter (SERT) in a neuropathic pain model; the increases in p-NR1 and SERT are reduced by physical activity or exercise.

The current study tested if p-NR1 and SERT expression increased in the RVM in a chronic muscle pain model, if blockade of SERT in the RVM reversed the hyperalgesia, and if short-duration physical activity activated mu-opioid receptors to prevent the development of analgesia and reductions in p-NR1 and SERT in the RVM.

Findings revealed that short-duration physical activity prevented secondary hyperalgesia of the paw, but not primary muscle hyperalgesia in an activity-induced pain model that was mediated by the activation of mu-opioid receptors. In sedentary mice, there was an increase in SERT expression in the RVM and blockade of SERT in the RVM after induction of the activity-induced pain model reversed the hyperalgesia, showing a functional role for the increases in SERT. Regular physical activity prevents increases in SERT expression in the RVM, and alterations in SERT by wheel running do not occur after the treatment of animals with naloxone or genetic deletion of mu-opioid receptors (MOR). Together, these data suggest an interaction between the serotonergic and opioidergic systems in the analgesic effects of regular physical activity.

These findings suggest that activity-induced hyperalgesia activates multiple parallel mechanisms in the brain stem that result in increases in excitatory neurotransmitter activity (increased p-NR1) and decreased availability of inhibitory neurotransmitters (increased SERT). As few as 5 days of physical activity modulate the alterations in SERT and reduce secondary hyperalgesia through the activation of MOR. Understanding the underlying mechanisms of how exercise increases pain and the ways in which exercise decreases pain could lead to new strategies to reduce enhanced pain related to unaccustomed exercise and provide a time course and scientific rationale for people with chronic pain so they can recognize the benefits of engaging in regular physical activity.

The Relationship of Sociodemographic and Psychological Variables with Chronic Pain Variables in a Low-Income Population

Andrea K. Newman, Benjamin P. Van Dyke, Calia A. Torres, Jacob W. Baxter, Joshua C. Eyer, Shweta Kapoor, Beverly E. Thorn; Department of Psychology, The University of Alabama, Tuscaloosa, AL; Capstone College of Nursing, The University of Alabama, Tuscaloosa; Department of Psychiatry and Behavioral Sciences, The University of Texas Health Science Center at Houston

Sociodemographic factors have been extensively examined for overall trends within chronic pain populations. In general, studies have demonstrated an increased vulnerability to the deleterious effects of pain among African Americans, people living in rural and low-income communities, and individuals with low educational attainment and literacy levels. Low-income settings present a complex array of health disparities because of patterns of low educational attainment and literacy, higher proportions of minorities, and the myriad effects of stress associated with low income.

This study examined the sociodemographic and psychological factors related to chronic pain in a sample of underserved patients receiving treatment at community health centers serving low-income patients in central Alabama. Depression and pain catastrophizing are associated with pain and disability; these investigators hypothesized that depression and catastrophizing would be significant mediators between demographic factors and pain-related variables.

Results indicated that the indirect effects of age on pain severity, pain interference, and disability/physical functioning through depression are significant. Increasing age was significantly associated with lower pain catastrophizing and depressive symptoms, which in turn were associated with decreased pain severity, interference, and disability. These findings suggest that in the context of low-income settings, with limited resources and high levels of stress, an individual’s appraisal of stressors and pain may be critically important. Although this study could not establish causality because it was cross-sectional in nature, these findings highlight the important role of depressive symptoms and pain catastrophizing in patients with multiple health disparities.

Perhaps within low-income communities in which almost all individuals encounter multiple obstacles to obtaining quality health-related services, affective and cognitive factors become even more important in pain management as well as the ability to navigate the health care system. Systems-level changes in the healthcare system such as integration of behavioral and primary health care and better training of healthcare professionals to identify and treat the multiple stressors associated with chronic pain, may be particularly beneficial for disadvantaged patients such as those represented in this study.


The Clinical Journal of Pain

Highlights from The Clinical Journal of Pain (Volume 33, No. 9, September 2017 Issue)

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Acupuncture for the Treatment of Chronic Pain in the Military Population: Factors Associated with Treatment Outcomes

Anthony Plunkett, Thomas Beltran, Chelsey Haley, Connie Kurihara, Amy McCoart, Louis Chen, Indy Wilkinson, and Steven P. Cohen; Womack Army Medical Center; Henry M. Jackson Foundation Defense and Veterans Pain Management Center, Fort Bragg, NC; Department of Math and Science, Lincoln Memorial University, Harrogate, TN; Walter Reed National Military Medical Center; Uniformed Services University of the Health Sciences, Bethesda; Johns Hopkins School of Medicine, Baltimore, MD

Much remains unknown about many complementary and alternative medicine (CAM) treatments. Acupuncture is one of the most commonly used CAM treatments for pain, with more than 10 million acupuncture procedures performed yearly in the United States. In 2010, the Pain Management Task Force was created to provide recommendations and guidelines for military pain treatment and research. One of the main aims was to increase research on CAM treatments, with a strong focus on acupuncture.

In this study, investigators conducted a multisite retrospective electronic medical record review to determine which (if any) characteristics can predict successful response to acupuncture. They hypothesized that certain demographic and clinical factors (eg, diagnosis, lesser disease burden, lack of coexisting psychopathology) would be associated with successful treatment and that these factors could be used to guide treatment and future study.

As expected, the outcome variable (treatment success) strongly correlated with posttreatment pain score. Treatment success also was significantly correlated with the use of stimulation needles, but no other variables (age, race/ethnicity, education, pain duration, pain location, pain type, injury status, number or length of acupuncture sessions, frequency of sessions, use of stimulation needles, opioid use, smoking status, obesity, presence of psychological comorbidities, or pain level at baseline) predicted treatment outcome. Of the patients analyzed, 42.3% had successful treatment outcomes. Although treatment groups did not differ on baseline pain scores, posttreatment pain scores were significantly lower for the successful treatment group.

The study population was unique in that it represented a young, very active, generally healthy group that often faces physical and psychosocial stressors that may be more pronounced than seen in a civilian cohort. In addition, medications typically used to treat chronic pain such as adjuvants and opioids often are discouraged for this population because of their potential for cognitive effects and, for opioids, physical dependence and addiction. As a result, there has been a strong emphasis on the use of CAM treatments in the military healthcare system.

Overall, no single outcome variable could predict a successful treatment outcome. However, the combination of baseline pain, number of psychological comorbidities, and use of stimulation needles correctly classified 60.6% of cases. These factors should be considered when identifying suitable CAM patients and designing future randomized trials. More studies with larger sample sizes are needed to determine the best clinical predictors of treatment outcome after acupuncture.

Smoking May Increase Postoperative Opioid Consumption in Patients Who Underwent Distal Gastrectomy with Gastroduodenostomy for Early Stomach Cancer: A Retrospective Analysis

Doo Hwan Kim, Jun Young Park, Myong-Hwan Karm, Heon-Yong Bae, Jae-Young Lee, Ho Soo Ahn, Kunhee Lee, and Jeong Gil Leem; Department of Anesthesiology and Pain Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea

Nicotine’s analgesic properties likely function through both central and peripheral nicotine acetylcholine receptors. Nicotine also acts via interactions with the endogenous opioid pathways. Although nicotine seems to have antinociceptive effects, several studies suggest that smokers demonstrate higher pain intensity and chronic pain incidence. Acute pain likely is substantial for smokers during the perioperative period, and postoperative analgesic use is higher for these patients.

To evaluate whether postoperative opioid requirements are higher for smokers, investigators retrospectively analyzed the opioid requirements of smokers who underwent laparoscopic distal gastrectomy with gastroduodenostomy for early stomach cancer. Primary end points were the differences in postoperative opioid consumption between male smokers and nonsmokers. Secondary end points were the occurrence of side effects according to smoking status. Numerical rating scale (NRS) scores among smokers were significantly higher than among nonsmokers on the day of surgery, and opioid consumption was much higher for smokers during the postoperative period (with the exception of postoperative day 1). Smokers needed more opioids than nonsmokers on postoperative day 2, and total opioid requirements for smokers also were higher.

Surgical time, remifentanil amount, NRS scores on the day of surgery, opioid consumption on all postoperative days, and total opioid consumption were significantly higher in current smokers or ex-smokers. Adequate administration of analgesics is very important to help ensure optimal outcomes. Smoking status appeared to increase the perception of pain and necessity for more postoperative opioid use regardless of amount of smoking in this study. Consequently, titration of postoperative opioid administration for patients who smoke can provide sufficient analgesia and good surgical outcomes. Postoperative nausea and vomiting was less common among smokers, but incidence of side effects was not significantly different for smokers and nonsmokers.

After adjusting for other clinical variables that influence opioid use, age, smoking status, and the amount of necessary intraoperative remifentanil were independent factors associated with increments of postoperative opioid consumption.


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