Central pain contributions in osteoarthritis: next steps for improving recognition and treatment?

There is increasing recognition that central pain sensitivity plays an important role in pain severity among patients with osteoarthritis. Murphy and colleagues identified clusters of patients with osteoarthritis according to pain severity and accompanying symptoms, and one of these groups appeared to have a greater degree of centrally mediated pain. This observation provides some evidence that patients with greater central pain contributions can be identified in routine clinical settings, but brief, evidence-based strategies are still needed to more readily and systematically identify these patients. There is also a need to develop new strategies and to further evaluate existing therapies (pharmacological and nonpharmacological) that target central aspects of osteoarthritis pain.

patients with OA do experience heightened pain sensitivity, with substantial intra-individual variability [2,3]. However, the vast majority of OA-related treatments target the periphery; for example, nonsteroidal anti-infl ammatory drugs act on local infl ammatory processes. While these medications also aff ect central pain mechanisms -either directly or indirectly through their infl uence on peripheral pain stimuli and sensitivity [4] -failure to more fully address central pain sensitization may be one reason for inadequate pain relief in some patients.
Th e study by Murphy and colleagues provides additional support that patients diff er in the degree to which central mechanisms contribute to OA-related pain and other symptoms [1]. Th e authors used a cluster analysis approach and identifi ed three subgroups of patients, one of which was characterized not only by the highest pain levels but also by other symptoms characteristic of centrally mediated pain. Th is is an interesting and clinically relevant approach to the question of central pain contribution, providing support to the notion that patients with greater central pain sensitivity could be identifi ed in routine care settings, without the use of formal pain threshold testing or other processes that would typically be utilized in research.
Given the mounting evidence for the importance of central pain sensitivity in OA [5], how can this be addressed in routine clinical care? Th ere is certainly a need to further educate clinicians (and particularly those in primary care, who typically provide fi rst-line treatment for OA) about the important role of central pain adaptations, basic signs of central pain sensitivity, and the utility of current treatments to address this aspect of pain. Cognitive behavioral pain management interventions have shown effi cacy for treating neuropathic pain, but these interventions are underutilized among patients with OA. Increased availability and use of these programs could be one practical step toward improving treatment of the central aspect of pain. Opioid analgesics act centrally and also have a role in OA treatment; despite their potential for adverse side eff ects, they may be an eff ective treatment for patients with a strong central

Abstract
There is increasing recognition that central pain sensitivity plays an important role in pain severity among patients with osteoarthritis. Murphy and colleagues identifi ed clusters of patients with osteoarthritis according to pain severity and accompanying symptoms, and one of these groups appeared to have a greater degree of centrally mediated pain. This observation provides some evidence that patients with greater central pain contributions can be identifi ed in routine clinical settings, but brief, evidence-based strategies are still needed to more readily and systematically identify these patients. There is also a need to develop new strategies and to further evaluate existing therapies (pharmacological and nonpharmacological) that target central aspects of osteoarthritis pain.
contribution to the pain experience. Th ere is also some evidence for use of duloxetine and other antidepressants in the treatment of OA-related pain, and these therapies may be most eff ective for patients with greater central contributions to pain. More data are needed, however, to determine the appropriateness and eff ectiveness of these medications in the treatment of OA, as well as guidelines for when and how they are best applied in this patient group.
Murphy and colleagues and other researchers have suggested that OA treatment regimens could be tailored according to patients' pain mechanisms (for example, relative contribution of peripheral vs. central contributions). Th is suggestion certainly seems appealing both in terms of clinical effi ciency and likelihood of treatment response. However, there are at least two areas in which additional research is needed to support this tailored treatment becoming a clinical reality. First, additional research is needed to both identify new strategies and further evaluate existing therapies (including pharmacological and nonpharmaco logical) that target central aspects of OA-related pain. Th is area of treatment development has lagged con siderably behind strategies to address peripheral aspects of pain. Second, brief and evidence-based strategies are needed to identify patients who have a stronger central component to OA-related pain. Th e study by Murphy and colleagues suggests this further research is possible, and other studies -for example, that by Gwilym and colleagues [6] -have used surveys to identify patients with neuro pathic pain symptoms. Th e existing screening tools are probably too cumbersome for busy care providers, however, and simpler methods are needed for clinicians to readily identify patients who may benefi t more from treatments that target central pain mechanisms.
In summary, treatment of central pain sensitivity is an area with great promise for improving pain management in at least a subset of patients with OA; eff orts are clearly needed to expand the evidence base for both identifi cation and treatment of central pain contributions.