Central pain processing in osteoarthritis: implications for treatment

Differences in self-reported signs related to central sensitization and pressure pain threshold related to knee osteoarthritis and sarcopenia

PURPOSE

Neuroinflammation, which occurs in knee osteoarthritis and sarcopenia, has attracted attention as a mechanism of central sensitization, but the relationship between central sensitization and these conditions has not been widely studied. This study investigates differences in self-reported signs of central sensitization and pressure pain threshold in individuals with knee osteoarthritis and sarcopenia.

METHODS

We examined 340 patients (mean age ± standard deviation: 76 ± 5.9, women were 86.9%) with knee osteoarthritis scheduled to undergo total knee arthroplasty. For comparison, 129 community-dwelling older people (mean age ± standard deviation: 76 ± 5.5, women were 68.9%) individuals without a history of knee osteoarthritis or any other diagnosed illnesses were matched for age and sex. We assessed central sensitization inventory-9, pressure pain threshold, pain-related factors, skeletal muscle mass index, and hand grip strength. ANCOVA using 2 (patients with knee osteoarthritis and community older people without knee osteoarthritis) × 2 (sarcopenia and robust) was performed to assess outcome measurements.

RESULTS

The prevalence of sarcopenia among patients with knee osteoarthritis was 50.3%. ANCOVA revealed an interaction effect for the central sensitization inventory-9. For the main effect of knee osteoarthritis, there was a significant difference in central sensitization inventory-9, and for the main effect of sarcopenia, there was a significant difference in pressure pain threshold.

CONCLUSIONS

Discrepancies in the evaluation of central sensitization were identified between knee osteoarthritis and sarcopenia. Individuals with knee osteoarthritis had elevated score of self-reported indications of central sensitization, whereas sarcopenic patients had reduced pressure pain thresholds.

Association between chronic pain with presarcopenia and central sensitization in Japanese community-dwelling older adults: A cross-sectional study

Older people with chronic pain are at higher risk of developing sarcopenia. Central sensitization (CS) has been implicated in chronic pain among community-dwelling older adults. However, a relationship between CS and chronic pain with sarcopenia has not been established. This cross-sectional study aimed to clarify the relationship between chronic pain with sarcopenia or presarcopenia and CS among community-dwelling older adults. We assessed chronic pain and sarcopenia in 104 older adults participating in community health checks. We defined sarcopenia using the Asian Working Group for Sarcopenia (AWGS) consensus recommendations based on the following outcomes: low muscle mass, low muscle strength, and slow gait speed. Pain-related assessments included pain intensity, the Pain Catastrophizing Scale, the CS Inventory-9, the pressure pain threshold, the Tampa Scale of Kinesiophobia-11, and the EuroQol 5-dimension 5-level (EQ5D-5L). Chronic pain was defined by related symptoms within the month prior to the health check that had continued for ≥ 3 months and corresponded to a numerical rating scale score of ≥ 1 at the site of maximum pain. The prevalence of chronic pain was 43.3%. In addition, the prevalence of chronic pain with sarcopenia or presarcopenia was 29.8%. A logistic regression analysis revealed that the pressure pain threshold (odds ratio: 0.82, 95% CI: 0.95-1.02) and the EQ5D-5L (odds ratio: 0.58, 95% CI: 0.36-0.76) were significantly associated with the presence of chronic pain with sarcopenia or presarcopenia. Chronic pain with sarcopenia or presarcopenia was affected by central sensitization. Therefore, CS should be evaluated in the elderly.

Joint synovial macrophages as a potential target for intra-articular treatment of osteoarthritis-related pain

Osteoarthritis is the most common form of joint disease and is one of the leading causes of chronic pain. Given the multi-factorial nature, numerous efforts have been made to clarify the multiple factors impacting the pain symptoms and joint pathology, including synovial macrophages in particular. Accumulating evidence from studies involving human participants and experimental animal models suggests that accumulating macrophages in synovial tissue are implicated in peripherally mediated pain sensitization of affected joints in osteoarthritis. Crosstalk between synovial macrophages and the innervating primary nociceptive neurons is thought to contribute to this facilitated pain processing by the peripheral nervous system. Due to high plasticity and complexity of synovial macrophages in the joint, safe therapies targeting single cells or molecules are currently lacking. Using advanced technologies (such as single-cell RNA sequencing and mass cytometry), studies have shown that diverse subpopulations of synovial macrophages exist in the distinct synovial microenvironments of specific osteoarthritis subtypes. Considerable progress has been made in delineating the molecular mechanisms of various subsets of synovial macrophages in the development of osteoarthritis. To develop a novel intra-articular treatment paradigm targeting synovial macrophages, we have summarized in this review the recent advances in identifying the functional consequences of synovial macrophage sub-populations and understanding of the molecular mechanisms driving macrophage-mediated remodeling.

Mechanism of Chronic Pain of Symptomatic Hip Osteoarthritis by Association of its Distribution, Nociceptive, Neuropathic, Nociplastic, or Mixed-pain Screening, and the Prevalence of Lumbar Spinal Stenosis: A Cross-sectional Study

OBJECTIVES

The pain of hip osteoarthritis (OA) is generally recognized as nociceptive in origin because of the local pathology. However, some patients with OA experience a neuropathic pain component as an essential part of some nociplastic pain subtype. Here, we sought to examine the mechanism of chronic pain of symptomatic hip OA by the association of its distribution, complex pain mechanism screening, and the prevalence of lumbar spinal stenosis.

MATERIALS AND METHODS

We conducted a prospective cross-sectional study of 100 hips in 100 patients with symptomatic hip OA in a chronic state. We examined all baseline clinical characteristics including clinical and functional score, location of pain and numbness, and pain score (PainDETECT questionnaire and the Leeds Assessment of Neuropathic Symptoms and Signs), and magnetic resonance imaging of the hip and lumbar spine.

RESULTS

The PainDETECT questionnaire and Leeds Assessment of Neuropathic Symptoms and Signs revealed that 23% of the patients had a neuropathic pain component. There were 24 variations of the pain pattern. By contrast, the pain localized around the hip joint was only 15%. Pain distal to the thigh and any numbness was significantly more frequent in the group with neuropathic pain (P<0.001). Lumbar spinal stenosis grade was not significantly different between patients with nociceptive pain and those with neuropathic pain. Pain score was significantly correlated with the pain in clinical and functional scores.

DISCUSSION

Among patients with symptomatic hip OA, the distribution of pain was various, and about 23% of patients had neuropathic, nociplastic, or mixed pain as a possibility for somatosensory system disturbances.

Methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system: a systematic review

ABSTRACT

Mechanism-based classification of pain has been advocated widely to aid tailoring of interventions for individuals experiencing persistent musculoskeletal pain. Three pain mechanism categories (PMCs) are defined by the International Association for the Study of Pain: nociceptive, neuropathic, and nociplastic pain. Discrimination between them remains challenging. This study aimed to build on a framework developed to converge the diverse literature of PMCs to systematically review methods purported to discriminate between them; synthesise and thematically analyse these methods to identify the convergence and divergence of opinion; and report validation, psychometric properties, and strengths/weaknesses of these methods. The search strategy identified articles discussing methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system. Studies that assessed the validity of methods to discriminate between categories were assessed for quality. Extraction and thematic analysis were undertaken on 184 articles. Data synthesis identified 200 methods in 5 themes: clinical examination, quantitative sensory testing, imaging, diagnostic and laboratory testing, and pain-type questionnaires. Few methods have been validated for discrimination between PMCs. There was general convergence but some disagreement regarding findings that discriminate between PMCs. A combination of features and methods, rather than a single method, was generally recommended to discriminate between PMCs. Two major limitations were identified: an overlap of findings of methods between categories due to mixed presentations and many methods considered discrimination between 2 PMCs but not others. The results of this review provide a foundation to refine methods to differentiate mechanisms for musculoskeletal pain.

Cost-effectiveness of duloxetine for knee OA subjects: the role of pain severity

OBJECTIVE

Establish the impact of pain severity on the cost-effectiveness of generic duloxetine for knee osteoarthritis (OA) in the United States.

DESIGN

We used a validated computer simulation of knee OA to compare usual care (UC) - intra-articular injections, opioids, and total knee replacement (TKR) - to UC preceded by duloxetine in those no longer achieving pain relief from non-steroidal anti-inflammatory drugs (NSAIDs). Outcomes included quality-adjusted life years (QALYs), lifetime medical costs, and incremental cost-effectiveness ratios (ICERs). We considered cohorts with mean ages 57-75 years and Western Ontario and McMaster Osteoarthritis Index (WOMAC) pain 25-55 (0-100, 100-worst). We derived inputs from published data. We discounted costs and benefits 3% annually. We conducted sensitivity analyses of duloxetine efficacy, duration of pain relief, toxicity, and costs.

RESULTS

Among younger subjects with severe pain (WOMAC pain = 55), duloxetine led to an additional 9.6 QALYs per 1,000 subjects (ICER = $88,500/QALY). The likelihood of duloxetine being cost-effective at willingness-to-pay (WTP) thresholds of $50,000/QALY and $100,000/QALY was 40% and 54%. Offering duloxetine to older patients with severe pain led to ICERs >$150,000/QALY. Offering duloxetine to subjects with moderate pain (pain = 25) led to ICERs <$50,000/QALY, regardless of age. Among knee OA subjects with severe pain (pain = 55) who are unwilling or unable to undergo TKR, ICERs were <$50,600/QALY, regardless of age.

CONCLUSIONS

Duloxetine is a cost-effective addition to knee OA UC for subjects with moderate pain or those with severe pain unable or unwilling to undergo TKR. Among younger subjects with severe pain, duloxetine is cost-effective at WTP thresholds >$88,500/QALY.

Subchondral bone osteoclasts induce sensory innervation and osteoarthritis pain

Joint pain is the defining symptom of osteoarthritis (OA) but its origin and mechanisms remain unclear. Here, we investigated an unprecedented role of osteoclast-initiated subchondral bone remodeling in sensory innervation for OA pain. We show that osteoclasts secrete netrin-1 to induce sensory nerve axonal growth in subchondral bone. Reduction of osteoclast formation by knockout of receptor activator of nuclear factor kappa-B ligand (Rankl) in osteocytes inhibited the growth of sensory nerves into subchondral bone, dorsal root ganglion neuron hyperexcitability, and behavioral measures of pain hypersensitivity in OA mice. Moreover, we demonstrated a possible role for netrin-1 secreted by osteoclasts during aberrant subchondral bone remodeling in inducing sensory innervation and OA pain through its receptor DCC (deleted in colorectal cancer). Importantly, knockout of Netrin1 in tartrate-resistant acid phosphatase-positive (TRAP-positive) osteoclasts or knockdown of Dcc reduces OA pain behavior. In particular, inhibition of osteoclast activity by alendronate modifies aberrant subchondral bone remodeling and reduces innervation and pain behavior at the early stage of OA. These results suggest that intervention of the axonal guidance molecules (e.g., netrin-1) derived from aberrant subchondral bone remodeling may have therapeutic potential for OA pain.

Peripheral Mechanisms Contributing to Osteoarthritis Pain

PURPOSE OF REVIEW

Osteoarthritis (OA) is the most common form of arthritis and a major source of pain and disability worldwide. OA-associated pain is usually refractory to classically used analgesics, and disease-modifying therapies are still lacking. Therefore, a better understanding of mechanisms and mediators contributing to the generation and maintenance of OA pain is critical for the development of efficient and safe pain-relieving therapies.

RECENT FINDINGS

Both peripheral and central mechanisms contribute to OA pain. Clinical evidence suggests that a strong peripheral nociceptive drive from the affected joint maintains pain and central sensitization associated with OA. Mediators present in the OA joint, including nerve growth factor, chemokines, cytokines, and inflammatory cells can contribute to sensitization. Furthermore, structural alterations in joint innervation and nerve damage occur in the course of OA. Several interrelated pathological processes, including joint damage, structural reorganization of joint afferents, low-grade inflammation, neuroplasticity, and nerve damage all contribute to the pain observed in OA. It can be anticipated that elucidating exactly how these mechanisms are operational in the course of progressive OA may lead to the identification of novel targets for intervention.

Spinal microglial activation in a murine surgical model of knee osteoarthritis

OBJECTIVE

Microgliosis, the activation of microglial cells, is thought to contribute to synaptic transmission in the dorsal horn and thereby promote chronic pain. The primary aim of this study was to document the temporal profile of dorsal horn microgliosis after destabilization of the medial meniscus (DMM) in wild type (WT) and Adamts5 null mice. Since neuronal fractalkine (CX3CL1) contributes to microgliosis, we assessed its release from dorsal root ganglia (DRG) cultures after DMM.

DESIGN

DMM or sham surgery was performed in the right knee of 10-week old male WT, CX3CR1-green fluorescent protein (GFP), or Adamts5 null C57BL/6 mice. Hind paw mechanical allodynia was monitored using von Frey fibers. L4 dorsal horn microgliosis was assessed 4, 8 and 16 weeks after surgery, based on the morphology of Iba1-immunoreactive microglia. DRG cells (L3-L5) were cultured and supernatants collected for fractalkine (FKN) ELISA.

RESULTS

In WT mice, numbers of activated microglia were increased 8 and 16 weeks, but not 4 weeks, after DMM but not sham surgery. DRG cultures showed increased basal FKN release at 8 and 16 weeks. Adamts5 null mice did not develop mechanical allodynia up to 16 weeks after DMM. Accordingly, DRG cultures from these mice did not exhibit increased FKN release and dorsal horn microgliosis did not occur.

CONCLUSION

DMM surgery leads to late stage dorsal horn microgliosis. The temporal correlation with DRG FKN release suggests it may contribute to microgliosis. Reduced microgliosis in Adamts5 null mice, which are protected from joint damage and associated mechanical allodynia after DMM, suggests that microgliosis is associated with joint damage and accompanying persistent pain.