Placebo responses in patients with peripheral neuropathic pain

Abstract

Abstract Background and aim Treatment responses during placebo periods in randomized clinical trials (RCTs) are quite often substantial and may impede a positive outcome of the trial. It would therefore be beneficial to gain more knowledge on factors contributing to large placebo responses in RCTs. The aim of the current study was to identify predictors of placebo responses in patients with peripheral neuropathic pain. Hypotheses We hypothesized that a high baseline pain intensity and variability will be predictive of large responses during placebo treatment. Furthermore, we hypothesized that expectation for pain relief, few prior treatments and side effects, low scores of pain catastrophizing, anxiety, depression and the personality trait neuroticism and high levels of positive emotions will be predictors of placebo responses. Methods This study is part of a randomized, double-blind, placebo-controlled, crossover study with the anticonvulsant oxcarbazepine. Pain intensity was registered at baseline and during treatment periods on a numerical rating scale (NRS, 0–10) along with expectation for pain relief (NRS), psychological measures (scores for anxiety, depression, catastrophizing, neuroticism, and positive emotions), prior treatments, and side effects. Results Multiple regression analysis with pain reduction during placebo treatment as the dependent variable and baseline pain, age, gender, and pain duration as explanatory variables was highly significant (R-squared = 0.53, p < 0.001), while other explanatory variables did not reach statistical significance. Further analyses will be carried out. Conclusions Age and gender were not significant predictors of placebo responses in this study. Further results will be presented at the congress. Acknowledgements This study is part of the Innovative Medicines Initiative project EUROPAIN, www.imi.europa.eu.