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Abstract: Ketamine is often used in pain clinics for refractory chronic pain, but its long-term efficacy is poorly reported. The main objective was to assess the long-term effect of ketamine on pain and health variables in patients with refractory chronic pain. A prospective, multicenter, 1-year follow-up observational study (NCT03319238) was conducted in 30 French pain clinics where ketamine is commonly prescribed. This study focused on patients with 1 ketamine delivery procedure (n = 256). The primary endpoint was pain intensity (0-10 numerical pain rating scale) before and after ketamine every month for 1 year. Secondary outcomes aimed to identify pain trajectories by semiparametric mixture models and to collect adverse events. The following data were obtained for 256 patients: Pain intensity decreased significantly (6.8 ± 1.8, n = 240 at baseline vs 5.7 ± 1.8, n = 93 at 12 months; P < 0.001). The effect size of the main endpoint was 0.61 (95% confidence interval: [0.40-0.80]; P < 0.001). Three pain trajectories were identified: 16.0% of patients in "mild pain" (mostly neuropathic pain), 35.3% in "moderate pain," and 45.7% in "severe pain" (mostly fibromyalgia) trajectory. Neuropathic pain and fibromyalgia presented opposite outcomes, pain severity being associated with anxiety, depression, and a poorer quality of life. Adverse events occurred at 1 week in 108/218 [50%] patients, and this rate gradually decreased throughout the follow-up. This real-life study in chronic pain identified distinct pain trajectories and predictive variables of ketamine efficacy. It is now pivotal to further study and optimize the subtyping of patients to provide the most effective and safe ketamine treatment in this vulnerable population., (Copyright © 2021 International Association for the Study of Pain.)

Background: An impairment of the peripheral nervous system has been suggested in fibromyalgia (FM). Noninvasive distal electrochemical skin conductance (ESC) has been studied little so far when combined with quantitative sensory testing (QST) in patients with FM., Methods: This study (clinicaltrials.gov NCT03347669) included 50 female patients with FM and 50 matched healthy volunteers (HVs). ESC (measured in microsiemens [µS] with Sudoscan), as well as psychological, quality of life, sleep, and social characteristics, were assessed in both groups. In a subgroup of 24 patients with FM and 24 HVs, QST of cold and warm detection and pain thresholds and diffuse noxious inhibitory controls (DNICs) were explored. Statistical analysis was performed for a 2-sided type I error at 5%., Results: Between patients with FM and HVs, ESC values differed (71.4 ± 11.2 µS vs. 74.4 ± 10.3 µS, respectively; P = 0.003), especially on the dominant hand (P = 0.03), where more patients with FM had ESC values < 66 µS than did HVs (P = 0.046). No difference was observed on feet. In patients with FM, all collected characteristics were impaired (P < 0.001), DNICs were less functional, detection thresholds occurred later, and pain thresholds occurred earlier. No correlation was observed between ESC and DNICs or with any parameter., Conclusion: This study shows that the sudomotor function is significantly impaired in patients with FM, especially on the dominant hand. This occurs in parallel with adjustments of detection and pain thresholds in the context of deficient spinal pain modulation. ESC values combined with QST values are relevant in the context of patients with FM and need to be explored further in this nociception-autonomic system intertwining., (© 2019 World Institute of Pain.)