How and for whom does supportive adjustment to multiple sclerosis cognitive-behavioural therapy work? A mediated moderation analysis.

The supportive adjustment for multiple sclerosis (saMS) randomised controlled trial showed cognitive behavioural therapy (CBT) reduced distress at 12-months compared to supportive listening (SL). Larger changes in distress and functional impairment following CBT occurred in participants with clinical distress at baseline. This secondary analysis investigates whether CBT treatment effects occur through pre-defined CBT mechanisms of change in the total cohort and clinically distressed subgroup. 94 participants were randomised to saMS CBT or SL. Primary outcomes were distress and functional impairment (12 months). Mediators included cognitive-behavioural variables at post-treatment (15 weeks). Structural equation mediation and mediated-moderation models adjusting for baseline confounders assessed mediation overall and by distress level. Significant mediation was found but only for those with clinical distress at baseline. Illness acceptance (-0.20, 95% confidence interval -0.01 to -0.46) and reduced embarrassment avoidance behaviours (-0.22, -0.02 to -0.58) mediated CBT's effect on distress. Changes in beliefs about processing emotions (-0.19, -0.001 to -0.46) mediated CBT's effect on functional impairment. saMS CBT had effects on distress and functional impairment via some of the hypothesised mechanisms drawn from a theoretical model of adjustment for MS but only among participants with clinical distress at baseline. Increasing acceptance and emotional expression and decreasing embarrassment avoidance improves MS adjustment.