The mediating effect of pain catastrophizing on pain intensity: the influence of the timing of assessments.

BACKGROUND: Pain catastrophizing underpins several psychosocial theories of pain, but there is limited evidence to support the proposal that changes in pain catastrophizing cause changes in pain. Results from mediation analyses have conflicting results, and one reason for these might be the timing of the assessment of pain catastrophizing. This study aimed to test the effect of the timing of pain catastrophizing on pain intensity. METHODS: Causal mediation analysis using data from a randomized controlled trial which included 100 participants with chronic low back pain. The trial found that clinical hypnosis, compared to pain education, reduced worst pain intensity and pain catastrophizing. In model 1, we used data from 2-week follow-up for pain catastrophizing and 3-month follow-up for pain. In model 2, we used data from 3-month follow-up for both pain catastrophizing and pain. RESULTS: The intervention had a significant average total effect on pain (-1.34 points, 95% CI -2.50 to -0.13). The average causal mediation effect was significant when pain catastrophizing and pain were measured at the same time (-0.62 points, 95% CI -1.30 to -0.11), but not significant when pain catastrophizing and pain intensity were measured at different times (-0.10 points, 95% CI -0.42 to 0.09). CONCLUSIONS: The timing of the assessment influenced the mediating role of pain catastrophizing on pain intensity. These results raise questions on the casual role that pain catastrophizing has on pain intensity. Psychosocial interventions such as clinical hypnosis can reduce pain intensity even when there has been no change in pain catastrophizing.