The phenotypic and genetic signatures of common musculoskeletal pain conditions

Update on the genetics of the fibromyalgia syndrome

Fibromyalgia syndrome (FMS), a condition characterized by chronic widespread pain and tenderness, is a complex condition considered to represent a paradigm of centralized pain. FMS has demonstrated a clear familial aggregation, and hence it is considered to have a genetic background. Multiple candidate-gene studies have been conducted in this field, focusing on target genes that play a role in the transmission and processing of pain. While many of these have focused in the past on markers related to neurotransmitter systems such as catecholamines (catechol-O-methyltransferase (COMT)) and serotonin, novel target genes have recently emerged. In addition, genome-wide sequencing scanning (genome-wide association study (GWAS)) is increasingly being harnessed for the study of chronic pain, including FMS. Micro RNAs are another novel field of research related to posttranscriptional inhibition of gene expression, which are currently regarding the pathogenesis of FMS.

Translational pain research: Lessons from genetics and genomics

Pharmacological, surgical, psychological, and alternative medicine approaches for the treatment of chronic pain, including neuropathic pain, provide only partial relief for most patients, with the efficacy of existing medications often blunted by dose-limiting side effects arising from drug actions on cells outside the pain-signaling axis. The development of more effective treatments for pain--particularly chronic pain states such as neuropathic pain--has been hampered by lack of predictive animal models and biomarkers, variation in pain characteristics between patients or on a day-to-day basis for single patients, patient stratification on the basis of symptoms rather than mechanism, and a high rate of placebo responses. We discuss genetic and genomic approaches to translational pain research. We review examples of the identification and validation of human pain targets through rodent genome-wide association studies (GWAS) and global mRNA expression studies, functional screening in flies and mice, human GWAS and whole-exome sequencing studies, and the targeted candidate gene approach. These and other emerging genetic and genomic strategies are likely to facilitate the development of new, more effective pain therapeutics.

Improving long-term outcomes for chronic low back pain: time for a new paradigm?

These are exciting times for physical therapists who treat people with chronic low back pain (CLBP). Many of the mysteries of this condition are starting to be revealed, and it appears that major breakthroughs are on the way. Advances in neuroimaging, coupled with increased understanding of the molecular and submolecular events associated with the symptoms of back pain, are helping us reconceptualize the etiologies and mechanisms of this condition. The result of these advances is that physical therapists now have a wide range of potential "treatment packages" that can include patient education, manual therapy, and a wide variety of exercise options for people with CLBP. The question is, "How can long-term, self-management programs become more effective?"

Psychological aspects of chronic musculoskeletal pain

Chronic musculoskeletal pain, by its very nature, is associated with negative emotions and psychological distress. There are individual differences in personality, coping skills, behavioral adaptation, and social support that dramatically alter the psychological outcomes of patients with chronic pain. Patients who have an aspect of central pain amplification associated with mechanical or inflammatory pain and patients with fibromyalgia (FM) are likely to exhibit higher levels of psychological distress and illness behaviors. This manuscript discusses several different constructs for the association between chronic pain, central pain amplification, and psychological distress. The first key question addresses mechanisms shared in common between chronic pain and mood disorders, including the individual factors that influence psychological comorbidity, and the second addresses how pain affects mood and vice versa. Finally, the utility of cognitive behavioral approaches in the management of chronic pain symptoms is discussed.

Biopsychosocial influence on shoulder pain: risk subgroups translated across preclinical and clinical prospective cohorts

Tailored treatment based on individual risk factors is an area with promise to improve options for pain relief. Musculoskeletal pain has a biopsychosocial nature, and multiple factors should be considered when determining risk for chronic pain. This study investigated whether subgroups comprised genetic and psychological factors predicted outcomes in preclinical and clinical models of shoulder pain. Classification and regression tree analysis was performed for an exercise-induced shoulder injury cohort (n = 190) to identify high-risk subgroups, and a surgical pain cohort (n = 150) was used for risk validation. Questionnaires for fear of pain and pain catastrophizing were administered before injury and preoperatively. DNA collected from saliva was genotyped for a priori selected genes involved with pain modulation (COMT and AVPR1A) and inflammation (IL1B and TNF/LTA). Recovery was operationalized as a brief pain inventory rating of 0/10 for current pain intensity and <2/10 for worst pain intensity. Follow-up for the preclinical cohort was in daily increments, whereas follow-up for the clinical cohort was at 3, 6, and 12 months postoperatively. Risk subgroups comprised the COMT high pain sensitivity variant and either pain catastrophizing or fear of pain were predictive of heightened shoulder pain responses in the preclinical model. Further analysis in the clinical model identified the COMT high pain sensitivity variant and pain catastrophizing subgroup as the better predictor. Future studies will determine whether these findings can be replicated in other anatomical regions and whether personalized medicine strategies can be developed for this risk subgroup.

Chronic Pain: Where the Body Meets the Brain

Chronic musculoskeletal pain is one of the most intractable clinical problems faced by clinicians and can be devastating for patients. Central pain amplification is perceived pain that cannot be fully explained on the basis of somatic or neuropathic processes and is due to physiologic alterations in pain transmission or descending pain modulatory pathways. In any individual, central pain amplification may complicate nociceptive or neuropathic pain. Furthermore, patients with somatic symptom disorders may have alterations in their psychological or behavioral responses to pain that contribute significantly to the clinical presentation. Genetic, physiologic, and psychological factors associated with central pain amplification are beginning to be understood. One important contributor to chronic pain is perceived stress and stress response systems. We and others have shown a complex relationship between the physiologic stress response and chronic pain symptoms. Unfortunately, treatments for chronic pain are woefully inadequate and often worsen clinical outcomes. Developing new treatment strategies for patients with chronic pain is of utmost urgency. This essay provides a framework for thinking about chronic pain and developing new treatment approaches.

TMD pain is partly heritable. A systematic review of family studies and genetic association studies

The aim of this study was to describe the current knowledge on the role of heritability in TMD pain through a systematic review of the literature, including familiar aggregation studies and genetic association studies. For the systematic search of the literature, the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) guidelines were followed. In total, 21 studies were included in the review, including five familiar aggregation studies and 16 genetic association studies. From both familiar aggregation studies and genetic association studies, modest evidence for the role of heritability in TMD pain was found. The literature mainly suggests genetic contributions from candidate genes that encode proteins involved in the processing of painful stimuli from the serotonergic and catecholaminergic system. This systematic review shows that the evidence for the role of heritability in the development of TMD pain is cumulating.

Persistent breast pain following breast cancer surgery is associated with persistent sensory changes, pain interference, and functional impairments

Interindividual variability exists in persistent breast pain following breast cancer surgery. Recently, we used growth mixture modeling to identify 3 subgroups of women (N = 398) with distinct persistent breast pain trajectories (ie, mild, moderate, severe) over 6 months following surgery. The purposes of this study were to identify demographic and clinical characteristics that differed among the breast pain classes and, using linear mixed effects modeling, to examine how changes over time and in sensitivity in the breast scar area, pain qualities, pain interference, and hand and arm function differed among these classes. Several demographic and clinical characteristics differentiated the breast pain classes. Of note, 60 to 80% of breast scar sites tested were much less sensitive than the unaffected breast. Significant group effects were observed for pain qualities and interference scores, such that, on average, women in the severe pain class reported higher scores than women in the moderate pain class. In addition, women in the moderate pain class reported higher scores than women in the mild pain class. Compared to women in the mild pain class, women in the severe pain class had significantly impaired grip strength, and women in the moderate and severe pain classes had impaired flexion and abduction.

PERSPECTIVE

Subgroups of women with persistent postsurgical breast pain differed primarily with respect to the severity rather than the nature or underlying mechanisms of breast pain. Pervasive sensory loss and the association between persistent breast pain and sustained interference with function suggest the need for long-term clinical follow-up.

A pain research agenda for the 21st century

Chronic pain represents an immense clinical problem. With tens of millions of people in the United States alone suffering from the burden of debilitating chronic pain, there is a moral obligation to reduce this burden by improving the understanding of pain and treatment mechanisms, developing new therapies, optimizing and testing existing therapies, and improving access to evidence-based pain care. Here, we present a goal-oriented research agenda describing the American Pain Society's vision for pain research aimed at tackling the most pressing issues in the field.

PERSPECTIVE

This article presents the American Pain Society's view of some of the most important research questions that need to be addressed to advance pain science and to improve care of patients with chronic pain.

The importance of psychological assessment in chronic pain

PURPOSE OF REVIEW

Much confusion has surrounded the purpose of the psychological assessment in the context of chronic pain. For many clinicians, the psychological assessment is used to rule out psychiatric illness and to identify the nonmedical causes for pain and disability. In essence, it is used to identify the causes of pain that fall outside of the biomedical model. Supported by over 30 years of evidence, the bio-psycho-social model acknowledges that psychosocial factors are inherent in chronic pain and require assessment if meaningful diagnostics and treatments are to occur.

RECENT FINDINGS

Five broad categories of psychosocial assessment are relevant to chronic pain. These categories have been shown to enhance the diagnosis of the underlying forms of pain, predict the transition from acute to chronic status, and help to phenotype individuals for the discovery of the underlying mechanisms responsible for pain.

SUMMARY

Informed assessment of chronic pain needs to include relevant biological, psychological, and social domains. This article describes those domains and offers suggestions of specific instruments to use in clinical or research settings.

Role for monocyte chemoattractant protein-1 in the induction of chronic muscle pain in the rat

While raised levels of monocyte chemoattractant protein 1 (MCP-1) have been observed in patients with chronic muscle pain, direct evidence for its role as an algogen in skeletal muscle is still lacking. In the rat, MCP-1 induces a dose-dependent mechanical hyperalgesia lasting for up to 6weeks. Following recovery, rats exhibited a markedly prolonged hyperalgesia to an intramuscular injection of prostaglandin E2, hyperalgesic priming. Intrathecal pretreatment with isolectin B4 (IB4)-saporin, which selectively destroys IB4-positive (IB4+) nociceptors, markedly decreased MCP-1-induced hyperalgesia and prevented the subsequent development of priming. To evaluate the involvement of MCP-1 in stress-induced chronic pain we administered, intrathecally, antisense (AS) or mismatch oligodeoxynucleotides directed against CCR2 (the canonical receptor for MCP-1) mRNA, during the exposure to water-avoidance stress, a model of stress-induced persistent muscle pain. The AS treatment attenuated this hyperalgesia, whereas IB4-saporin abolished water-avoidance stress-induced muscle hyperalgesia and prevented stress-induced hyperalgesic priming. These results indicate that MCP-1 induces persistent muscle hyperalgesia and a state of latent chronic sensitization to other algogens, by action on its cognate receptor on IB4+ nociceptors. Because MCP-1 also contributes to stress-induced widespread chronic muscle pain, it should be considered as a player in chronic musculoskeletal pain syndromes.

Is it all about a pain in the back?

Multisite musculoskeletal pain is common among people suffering from low back pain. Although the mechanisms behind co-occurrence of multiple somatic symptoms and musculoskeletal pain are still unknown, patients with co-morbidities and co-occurring musculoskeletal symptoms tend to have worse functional status, a poorer prognosis and respond less favourably to treatment. Evidence also suggests that the more pain sites a patient reports, the more reduced their physical and mental function will be regardless of location of pain. At the same time, evidence suggests that strategies for diagnosis and treatment of low back pain and other musculoskeletal disorders such as neck pain and lower limb osteoarthritis are very similar. In this chapter, we discuss the prevalence, consequences, and implications of commonalities between low back pain, pain in other sites and co-occurring pain. In addition, we propose a conceptual framework for a common stepwise approach to the diagnosis and management of back and musculoskeletal pain.