• Thomas J P Mangnus, Maaike Dirckx, Krishna D Bharwani, Cecile C de Vos, FrankemaSander P GSPGCenter for Pain Medicine, Erasmus MC University Medical Center, Rotterdam, The Netherlands., Dirk L Stronks, and HuygenFrank J P MFJPMCenter for Pain Medicine, Erasmus MC University Medical Center, Rotterdam, The Netherlands..
• Center for Pain Medicine, Erasmus MC University Medical Center, Rotterdam, The Netherlands.
• Pain Pract. 2021 Nov 1; 21 (8): 890-897.

ObjectiveThe objective of this study was to assess the effectiveness of a low-dose intravenous S-ketamine treatment on refractory pain in patients with Complex Regional Pain Syndrome (CRPS).MethodsIn this retrospective study, patients with CRPS who received intravenous S-ketamine from March 2010 to April 2019 were included. According to our inpatient protocol, S-ketamine dose was increased until pain reduction was achieved or side effects were observed. Maximum dose was 14 mg/h and treatment duration was 7 days. Primary outcome parameters were pain scores (Numeric Rating Scale) at baseline (T0), end of infusion (T1), and approximately 4 weeks postinfusion (T2). Patients were categorized as responder/nonresponder at T1 and T2. Patients were considered a responder in case there was pain score reduction of greater than or equal to 2 points or if treatment was reported as successful.ResultsForty-eight patients were included. Mean disease duration was 5 years (interquartile range [IQR] = 6 years). Median pain score significantly decreased from 8 (IQR = 2) at T0 to 6 (IQR = 4) at T1 (p < 0.001). At T1, 62% of the patients were responders. At T2, 48% of the patients remained a responder. A significant proportion of the responders at T1 turned into nonresponders at T2 (p = 0.03).ConclusionIn a group of patients with CRPS with refractory pain, low-dose intravenous S-ketamine treatment resulted in effective pain relief during infusion. Although a significant proportion of initial responders became nonresponders at follow-up, half of the patients were still a responder at ~ 4 weeks postinfusion. Further research is needed to investigate mechanisms responsible for pain relief by S-ketamine infusions and to ascertain possible predictors of response to the treatment.© 2021 The Authors. Pain Practice published by Wiley Periodicals LLC on behalf of World Institute of Pain.

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