Pain medicine basics: Overview

Neuromodulation: Technology at the Neural Interface is the preeminent journal in the area of neuromodulation, providing our readership with the state of the art clinical, translational and basic science research in our field and representing the needs of the broad neuromodulation community. For clinicians, engineers, scientists and members of the biotechnology industry alike, Neuromodulation provides timely and rigorously peer reviewed articles on the technology, science and clinical application of devices that interface with the nervous system to treat disease and improve function. Neuromodulation covers an ever expanding field including pain, headache, movement disorders, spasticity, paralysis, psychiatric disorders, epilepsy, sensory deprivation, gastric dysfunction, obesity and incontinence.

Regional Anesthesia & Pain Medicine, the official publication of the American Society of Regional Anesthesia and Pain Medicine (ASRA Pain Medicine), is a monthly journal that publishes peer-reviewed scientific and clinical studies to advance the understanding and clinical application of regional techniques for surgical anesthesia and postoperative analgesia. Coverage includes intraoperative regional techniques, perioperative pain, chronic pain, obstetric anesthesia, paediatric anesthesia, outcome studies, and complications.

Abstract
The perception of pain and ability to cope with it varies widely amongst people, which in part could be due to the presence of inhibitory (antinociceptive) or facilitatory (pronociceptive) effects in conditioned pain modulation (CPM). This study examined whether individual differences in CPM reflect functional connectivity (FC) strengths within nodes of the descending antinociceptive pathway (DAP). A heat-based CPM paradigm and resting-state functional magnetic resonance imaging (rs-fMRI) were used to test the hypothesis that an individual's capacity to exhibit inhibitory CPM (changes in test stimuli [TS] pain due to a conditioning stimulus [CS]) reflects FC of the subgenual anterior cingulate cortex (sgACC), periaqueductal gray (PAG), and rostral ventromedial medulla (RVM). A total of 151 healthy participants (72 men, 79 women) underwent CPM testing and rs-fMRI. Three types of CPM were identified based on the effect of the CS on TS pain: (1) Antinociception: CS reduced TS pain in 45% of participants, (2) No-CPM: CS did not change TS pain in 15% of participants, and (3) Pronociception: CS increased TS pain in 40% of participants. Only the Antinociceptive subgroup exhibited FC between the left sgACC and PAG, right sgACC and PAG, and RVM and PAG. Furthermore, only the Antinociceptive subgroup exhibited a correlation of both left and right sgACC-RVM FC (medium effect sizes) with CPM effect magnitude. Women, compared with men were more likely to be categorized as pronociceptive. These data support the proposition that FC of the DAP reflects or contributes to inhibitory CPM.

Abstract
Objective: Complex Regional Pain Syndrome (CRPS) presents significant diagnostic challenges due to its diverse clinical presentation. This study aims to describe the diagnostic trajectory of patients labeled with CRPS, focusing on referral patterns, application of the Budapest criteria, and accuracy of CRPS diagnosis.

Methods: A retrospective study was conducted of 53 patients treated for CRPS at a peripheral nerve clinic within a tertiary care center (2020-2024). Patient demographics, referral patterns, events leading to CRPS diagnosis, and diagnostic tests were analyzed. Three clinicians (two plastic surgeons, one pain medicine specialist) retrospectively assessed the validity of CRPS diagnoses using the Budapest criteria. Inter-rater reliability (IRR) for CRPS presence and type was calculated using Cohen's kappa (κ).

Results: Among the 53 patients, the median time from the first mention of CRPS to referral to the nerve clinic was 1.3 years (IQR:0.4-3.6). The Budapest criteria had been assessed in 26% of patients pre-evaluation. In 33% of patients labeled with CRPS type I, an inciting nerve injury was identified. Following retrospective assessment, 42% of patients were determined to have CRPS by all raters, 26% were determined not to have CRPS, and 32% showed inconsistent agreement. The IRR for CRPS diagnosis and type ranged from minimal to moderate (κ=0.32-0.72).

Discussion: Our findings highlight variability in the application of the Budapest criteria for CRPS diagnosis, as well as inconsistencies in its retrospective application. Potentially treatable peripheral nerve injuries should be addressed prior to CRPS diagnosis. These findings may help improve early diagnostic assessment in patients with chronic pain.