The relationship between regional pain with or without neuropathic symptoms and chronic widespread pain

Application of the IASP Grading System to Identify Underlying Pain Mechanisms in Patients With Knee Osteoarthritis: A Prospective Cohort Study

OBJECTIVES

This study aimed to apply the International Association for the Study of Pain (IASP) grading system for identifying nociplastic pain in knee osteoarthritis (KOA) awaiting total knee arthroplasty (TKA) and propose criteria to fine-tune decision-making. In addition, the study aimed to characterize a "probable" versus "no or possible" nociplastic pain mechanism using biopsychosocial variables and compare both groups in their 1-year post-TKA response.

METHODS

A secondary analysis of baseline data of a longitudinal prospective study involving 197 patients with KOA awaiting total TKA in Belgium and the Netherlands was performed. Two approaches, one considering 4 and the other 3 pain locations (step 2 of the grading system), were presented. Linear mixed model analyses were performed to compare the probable and no or possible nociplastic pain mechanism groups for several preoperative biopsychosocial-related variables and 1-year postoperative pain. Also, a sensitivity analysis, comparing 3 pain mechanism groups, was performed.

RESULTS

Thirty (15.22%-approach 4 pain locations) and 46 (23.35%-approach 3 pain locations) participants were categorized under probable nociplastic pain. Irrespective of the pain location approach or sensitivity analysis, the probable nociplastic pain group included more woman, was younger, exhibited worse results on various preoperative pain-related and psychological variables, and had more pain 1-year post-TKA compared with the other group.

DISCUSSION

This study proposed additional criteria to fine-tune the grading system for nociplastic pain (except for discrete/regional/multifocal/widespread pain) and characterized a subgroup of patients with KOA with probable nociplastic pain. Future research is warranted for further validation.

Ventral posteromedial nucleus of the thalamus gates the spread of trigeminal neuropathic pain

BACKGROUND

Widespread neuropathic pain usually affects a wide range of body areas and inflicts huge suffering on patients. However, little is known about how it happens and effective therapeutic interventions are lacking.

METHODS

Widespread neuropathic pain was induced by partial infraorbital nerve transection (p-IONX) and evaluated by measuring nociceptive thresholds. In vivo/vitro electrophysiology were used to evaluate neuronal activity. Virus tracing strategies, combined with optogenetics and chemogenetics, were used to clarify the role of remodeling circuit in widespread neuropathic pain.

RESULTS

We found that in mice receiving p-IONX, along with pain sensitization spreading from the orofacial area to distal body parts, glutamatergic neurons in the ventral posteromedial nucleus of the thalamus (VPMGlu) were hyperactive and more responsive to stimulations applied to the hind paw or tail. Tracing experiments revealed that a remodeling was induced by p-IONX in the afferent circuitry of VPMGlu, notably evidenced by more projections from glutamatergic neurons in the dorsal column nuclei (DCNGlu). Moreover, VPMGlu receiving afferents from the DCN extended projections further to glutamatergic neurons in the posterior insular cortex (pIC). Selective inhibition of the terminals of DCNGlu in the VPM, the soma of VPMGlu or the terminals of VPMGlu in the pIC all alleviated trigeminal and widespread neuropathic pain.

CONCLUSION

These results demonstrate that hyperactive VPMGlu recruit new afferents from the DCN and relay the extra-cephalic input to the pIC after p-IONX, thus hold a key position in trigeminal neuropathic pain and its spreading. This study provides novel insights into the circuit mechanism and preclinical evidence for potential therapeutic targets of widespread neuropathic pain.

Predictors of Persistent Somatic Symptoms in the General Population: A Systematic Review of Cohort Studies

OBJECTIVE

Up to 10% of the general population experiences persistent somatic symptoms (PSS). Numerous studies in a variety of health domains are dedicated to identifying factors that are associated with PSS onset. The present study aimed to provide an overview of predictors for PSS onset in the general population and the related health domains.

METHODS

A systematic search was performed identifying longitudinal cohort studies that examined factors associated with PSS onset in the general population. Included studies measured potential predictors before PSS onset and were categorized according to the dynamic biopsychosocial model. Four levels of evidence were discerned for predictors, based on the number of studies and percentage of consistent findings.

RESULTS

In the 154 articles eligible for analysis, 27 PSS subtypes were studied, with primary focus on fibromyalgia (25.0%) and irritable bowel syndrome (23.3%). Of the >250 predictors of PSS onset, 46 were investigated more than once and showed consistent results. Strong evidence identifies biological (e.g., infections, body weight-related metrics), psychological (e.g., sleep problems, psychopathology), interpersonal (life events, childhood/interpersonal stress), contextual (employment), and health behavioral (health care utilization) predictors.

CONCLUSIONS

The results provide strong evidence for factors from all dynamic biopsychosocial domains, although interpersonal and health behavioral factors are relatively under investigated. Thus, evidence suggests that reduction of predictors of PSS onset to a specific factor/domain may be too restrictive. There is no evidence that this differs per PSS subtype. Exploring all domains and measuring common factors across subtypes are essential to improve the clinical course of PSS.

Comorbidities and use of analgesics in people with knee pain: a study in the Nottingham Knee Pain and Health in the Community (KPIC) cohort

Objectives

The aims were to examine the prevalence of comorbidities and role of oral analgesic use in people with knee pain (KP) compared with those without.

Methods

The Knee Pain and related health In the Community (KPIC) cohort comprises community-derived adults aged ≥40 years, irrespective of knee pain. Thirty-six comorbidities across 10 systems were compared between people with KP and controls without KP or knee OA. Multivariable logistic regression analysis was used to determine the adjusted odds ratio (aOR) and 95% CI for multimorbidity (at least two chronic conditions) and each specific comorbidity. Both prescribed and over-the-counter analgesics were included in the model, and their interactions with KP for comorbidity outcomes were examined.

Results

Two thousand eight hundred and thirty-two cases with KP and 2518 controls were selected from 9506 baseline participants. The mean age of KP cases was 62.2 years, and 57% were women. Overall, 29% of the total study population had multimorbidity (KP cases 34.4%; controls 23.8%). After adjustment for age, sex, BMI and analgesic use, KP was significantly associated with multimorbidity (aOR 1.35; 95% CI 1.17, 1.56) and with cardiovascular (aOR 1.25; 95% CI 1.08, 1.44), gastrointestinal (aOR 1.34; 95% CI 1.04, 1.92), chronic widespread pain (aOR 1.54; 95% CI 1.29, 1.86) and neurological (aOR 1.32; 95% CI 1.01, 1.76) comorbidities. For multimorbidity, the use of paracetamol and opioids interacted positively with KP, whereas the use of NSAIDs interacted negatively for seven comorbidities.

Conclusion

People with KP are more likely to have other chronic conditions. The long-term benefits and harms of this change remain to be investigated.

Trial registration

ClinicalTrials.gov, http://clinicaltrials.gov, NCT02098070.

The autoimmune aetiology of unexplained chronic pain

Chronic pain is the leading cause of life years lived with disability worldwide. The aetiology of most chronic pain conditions has remained poorly understood and there is a dearth of effective therapies. The WHO ICD-11 has categorised unexplained chronic pain states as 'chronic primary pains' (CPP), which are further defined by their association with significant distress and/or dysfunction. The new mechanistic term, 'nociplasticic pain' has been developed to illustrate their presumed generation by a structurally intact, but abnormally functioning nociceptive system. Recently, researchers have unravelled the surprising, ubiquitous presence of pain-sensitising autoantibodies in four investigated CPP indicating autoimmune causation. In persistent complex regional pain syndrome, fibromyalgia syndrome, chronic post-traumatic limb pain, and non-inflammatory joint pain associated with rheumatoid arthritis, passive transfer experiments have shown that either IgG or IgM antibodies from patient-donors cause symptoms upon injection to rodents that closely resemble those of the clinical disorders. Targets of antibody-binding and downstream effects vary between conditions, and more research is needed to elucidate the molecular and cellular details. The central nervous system appears largely unaffected by antibody binding, suggesting that the clinically evident CNS symptoms associated with CPP might arise downstream of peripheral processes. In this narrative review pertinent findings are described, and it is suggested that additional symptom-based disorders might be examined for the contribution of antibody-mediated autoimmune mechanisms.