Positive and negative affective states and disease activity in ankylosing spondylitis.

The aim of the study was to explore the influence of psychological affective states such as cheerfulness and bad mood on self-reported disease activity in patients with ankylosing spondylitis (AS) while controlling for demographic and clinical variables. Patients attending a biological therapy unit were selected for a cross-sectional study if they met the criteria for AS and were already receiving treatment. Their psychological affective state was assessed with the state version of the State-Trait Cheerfulness Inventory. Clinical variables included were patient-reported disease activity using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and acute-phase reactants. We performed univariate and multivariate analyses to verify the robustness of the relationship between psychological affective states and disease activity. We also explored whether disease activity, measured either by self-report or by acute-phase reactants, was influenced by patient's overall affective state. In the recruited 31 patients with AS, overall affective state contributed significantly to the variance in BASDAI scores, adding 21.8% to the overall R-square of the predictive power of clinical and demographic variables (combined R-square = 17%). A higher positive affective state was associated with lower values of C-reactive protein (p < 0.05). Results of a bootstrapping procedure showed that the relationship between C-reactive protein levels and BASDAI scores was mediated by overall affective state. In patients with AS, affective state can induce variability in self-reported disease activity. Patients' overall affective state can explain the relationship between acute-phase reactants and self-reported scores. These findings suggest interesting possibilities for the monitoring of disease activity in AS.