Introduction

Monoaminergic activity modulates nociceptive transmission in the central nervous system (CNS). Although pain is the most disabling symptom of osteoarthritis (OA), limited knowledge exists regarding the CNS mechanisms that amplify pain and drive sensitization processes in humans.

Objectives

The main objective of this study was to evaluate associations between cerebrospinal fluid (CSF) monoamine metabolites, pain severity, and central sensitization in patients with OA undergoing total hip arthroplasty (THA).

Methods

Patients with OA (n = 52) and pain-free controls (n = 30) provided CSF samples for measurement of serotonin (5-hydroxyindoleacetic acid [5-HIAA]), noradrenaline (3-methoxy-4-hydroxyphenylglycol [HMPG]), and dopamine (homovanillic acid [HVA]) monoamine metabolites. Patients with OA completed longitudinal evaluation of pain using clinical measures and quantitative sensory testing.

Results

Patients with OA had higher HMPG levels when compared with controls (P = 0.036). Within patients with OA undergoing THA, higher 5-HIAA and HVA levels were consistently associated with higher preoperative pain severity. Higher concentrations of 5-HIAA and HVA were also associated with lower conditioned pain modulation levels, whereas higher HMPG levels were linked to more efficient conditioned pain modulation. Patients with higher levels of CSF HVA exhibited increased pressure pain sensitivity (arm pressure pain detection threshold < 250 kPa vs ≥ 250 kPa, P = 0.042). Higher preoperative levels of CSF 5-HIAA predicted poorer pain control 6 months postoperatively (brief pain inventory pain severity; adjusted β = 0.010, 95% CI 0.001-0.019).

Conclusions

In OA patients with disabling pain, higher CSF levels of serotonin and dopamine metabolites are associated with increased pain severity and central sensitization. Increased noradrenergic activity may be associated with more efficient pain inhibitory capacity.

Systemic inflammation is associated with increasing age. Yet, there are limited data about the association between age and systemic inflammation within older adults, and whether older age is also associated with cellular and nuclear signaling markers of inflammation. In community-dwelling older adults (N = 262, 60-88 years), systemic levels of C-reactive protein, interleukin-6, and soluble tumor necrosis factor receptor II; levels of toll-like receptor-4-stimulated monocytic production of interleukin-6 and tumor necrosis factor α; and resting nuclear levels of activated nuclear factor kappa B and signal transducer and activator of transcription (STAT1, STAT3, STAT5) were evaluated. Adjusting for demographic and clinical factors, multivariate linear regression tested the association between age and each inflammatory marker. Age was positively associated with increased levels of interleukin-6 and soluble tumor necrosis factor receptor II (p's < .05) and with increases in STAT1, STAT3, and STAT5 activation (p's < .05). However, no relationship was found between age and C-reactive protein, toll-like receptor-4-stimulated interleukin-6/tumor necrosis factor alpha α production, or nuclear factor kappa B. Within a community-dwelling sample of older adults, older age is associated with increases in STAT activation, along with increases of systemic inflammatory cytokines. In older adults, heterogeneity in age-related increases in inflammatory disease risk may be related to individual variability in inflammation.