Anxiety and depression affect performance on the symbol digit modalities test over time in MS and other immune disorders

BACKGROUND: Longitudinal studies assessing depression and anxiety effects on cognition in multiple sclerosis (MS) are limited. OBJECTIVE: We tested whether within-person fluctuations in symptoms of depression or anxiety over time affect cognition in persons with MS, inflammatory bowel disease (IBD), rheumatoid arthritis (RA), and a lifetime history of depression/anxiety disorders (DEP/ANX) but without an immune-mediated inflammatory diseases (IMID). METHODS: We followed participants (MS: 255, IBD: 247, RA: 154, and DEP/ANX: 306) for 3 years. Annually, they completed the hospital anxiety and depression scale (HADS) and cognitive tests including the symbol digit modalities test (SDMT). We evaluated associations of elevated symptoms (scores ⩾ 11) of anxiety (HADS-A) and depression (HADS-D) with SDMT z-scores using multivariable linear models—estimating between-person and within-person effects. RESULTS: Participants with MS performed worse on the SDMT than participants in the DEP/ANX cohort (β = −0.68; 95% CI: −0.88, −0.48). Participants with elevated HADS-A scores performed worse on the SDMT than those without elevated scores (β = −0.43; 95% CI: −0.65, −0.21), particularly those with RA. Time-varying within-person elevations in depressive symptoms were associated with worse SDMT performance (β = −0.12; 95% CI: −0.21, −0.021). CONCLUSIONS: Across persons, elevated symptoms of anxiety adversely affected information processing. Elevated symptoms of depression within-persons over time were associated with declines in information processing speed.