Catastrophizing and treatment outcome: Differential impact on response to placebo and active treatment outcome

Background: The primary objective of this study was to examine the differential impact of catastrophic thinking on response to placebo and active treatment in the context of a clinical trial for the treatment of neuropathic pain. Secondary objectives included examination of specific dimensions of catastrophic thinking that influence response to placebo and active treatment. Methods: A sample of 46 patients (26 men, 20 women) with neuropathic pain were randomly assigned to a placebo (n = 24) or treatment (amitriptyline + ketamine) condition (n = 22). All patients completed the Pain Catastrophizing Scale prior to treatment. Results: There were no significant differences between placebo and active treatment on pain reduction. In the placebo condition, high scores on the PCS were associated with greater pain reduction (r = 0.42, p < 0.05), while in the treatment condition, higher PCS scores were associated with less pain reduction (r = -0.51, p < 0.01). Additional analyses revealed that individuals in the active treatment condition reported slightly more side effects than individuals in the placebo condition, and that catastrophizing was significantly correlated with the report of side effects (r = 0.29, p < 0.05). Conclusion: Catastrophizing appears to have a differential impact on treatment response to placebo and active treatment. Given that side effects are more likely with active treatments than placebos, high levels of catastrophizing might impact negatively on active treatment effects but not necessarily on placebo effects. Discussion addresses how pain catastrophizing may contribute to null findings in clinical trials of interventions for pain disorders.