Human Studies

Prescribers are often confronted with the decision to escalate opioid doses to achieve adequate analgesia. Understanding the impact of dose escalation on pain intensity is warranted. Using a retrospective cohort study design, Veterans with chronic pain and chronic opioid therapy were identified. Opioid dose escalators (>20% increase in average morphine milligram equivalent [MME] daily dose) were compared to dose maintainers (±20% change in average MME daily dose) assessed over two consecutive 6 month windows. Pain intensity was measured by the Numeric Rating Scale (NRS). The primary analyses used linear repeated measures models among a 1:1 matched sample of escalators and maintainers matched on propensity score and within ±180 days of the index date. Sensitivity analyses were conducted using adjusted linear repeated measures models with and without incorporating stabilized inverse probability of treatment weighting (SIPTW). There were 32,420 dose maintainers and 20,767 dose escalators identified with 19,358 (93%) matched pairs. Pain scores were persistently higher among dose escalators at each 90 day time period after the index date (0-90 Days After Index Date: Dose Escalators:4.68, 95%CI: 4.64, 4.72 Dose Maintainers:4.32, 95%CI: 4.28, 4.36, p<0.0001; 91-180 Days After Index Date: Dose Escalators:4.53, 95%CI: 4.49, 4.57; Dose Maintainers:4.25, 95%CI: 4.22, 4.29, p<0.0001) but were not different in the 90 days prior to the index date (Dose Escalators:4.64, 95%CI: 4.61, 4.68; Dose Maintainers:4.59, 95%CI: 4.55, 4.63, p=0.0551). Sensitivity analyses provided similar results as the primary analyses. Opioid dose escalation among patients with chronic pain is not associated with improvements in NRS pain scores.

Some individuals with chronic pain experience improvement in their pain with treatment, whereas others do not. The neurobiological reason is unclear, but an understanding of brain structure and functional patterns may provide insights into pain's responsivity to treatment. In this investigation, we used magnetic resonance imaging (MRI) techniques to determine grey matter density alterations on resting functional connectivity (RFC) strengths between pain responders and nonresponders in patients with complex regional pain syndrome. Brain metrics of pediatric patients at admission to an intensive pain rehabilitative treatment program were evaluated. Pain responders reported significant pain improvement at discharge and/or follow-up whereas nonresponders reported no improvements in pain, increases in pain, or emergence of new pain symptoms. The pain (responder/nonresponder) groups were compared with pain-free healthy controls to examine predictors of pain responder status via brain metrics. Our results show: (1) on admission, pain nonresponders had decreased grey matter density (GMD) within the nucleus accumbens (NAc) and reduced RFC strength between the NAc and the dorsolateral prefrontal cortex vs. responders; (2) Connectivity strength was positively correlated with change in pain intensity from admission to discharge; (3) Compared with pain-free controls, grey matter and RFC differences emerged only among pain nonresponders; and (4) Using a discriminative model, combining GMD and RFC strengths assessed at admission showed the highest prediction estimate (87%) on potential for pain improvement, warranting testing in a de novo sample. Taken together, these results support the idea that treatment responsiveness on pain is underpinned by concurrent brain structure and resting brain activity.

Choosing perioperative suitable treatments requires reliable and valid outcome measurements. The International Pain Outcome (IPO) questionnaire has been widely used for quality improvement and research purposes within the PAIN-OUT network that has collected more than 550,000 data sets of postoperative patients in 200 hospitals worldwide. Our aim is to confirm psychometric properties of the Spanish version of the IPO questionnaire and its invariance by pain predictors.

Temporomandibular disorder (TMD) is one of the most common orofacial pain conditions. Alteration in immune functioning is one promising biological mechanism underlying pain in TMD. However, there is a gap in the understanding of molecular bases contributing to altered immune functioning in these patients.

Chronic low back pain (cLBP) that cannot be attributable to a specific pathoanatomical change is associated with high personal and societal costs. Still, the underlying mechanism that causes and sustains such a phenotype is largely unknown. Emerging evidence suggests that epigenetic changes play a role in chronic pain conditions. Using reduced representation bisulfite sequencing (RRBS), we evaluated DNA methylation profiles of adults with non-specific cLBP (n = 50) and pain-free controls (n = 48). We identified 28,325 hypermethylated and 36,936 hypomethylated CpG sites (p < 0.05). After correcting for multiple testing, we identified 159 DMRs (q < 0.01and methylation difference > 10%), the majority of which were located in CpG island (50%) and promoter regions (48%) on the associated genes. The genes associated with the differentially methylated regions were highly enriched in biological processes that have previously been implicated in immune signaling, endochondral ossification, and G-protein coupled transmissions. Our findings support inflammatory alterations and the role of bone maturation in cLBP. This study suggests that epigenetic regulation has an important role in the pathophysiology of non-specific cLBP and a basis for future studies in biomarker development and targeted interventions.