Objective:

To evaluate the predictive value of cognitive processing speed (CPS) via the Symbol Digit Modalities Test (SDMT) on time to disease progression as determined by the Expanded Disability Status Scale (EDSS) in people living with multiple sclerosis (PlwMS).

Background:

CPS correlates with multiple physical, emotional, and functional outcomes in PlwMS. Recent studies suggest that CPS can be predictive of long-term physical disability. Clarification of the predictive value of CPS on physical disability in MS would improve the process of making a disease course prognosis and could aid in identifying opportunities for early therapeutic intervention.

Design/Methods:

Eligible participants were PlwMS enrolled in the Comprehensive Longitudinal Investigation of Multiple Sclerosis at the Brigham (CLIMB) Study with relapsing-remitting, secondary progressive, or primary progressive MS, with regular EDSS assessments, and who had SDMT values at 2 timepoints at least 2-years apart. The association between baseline SDMT scores and time to EDSS values of 3.0, 4.0, 6.0 and 7.0 was estimated using Cox proportional hazards models.

Results:

A total of 624 PlwMS had at least 2 SDMT scores separated by at least 2 years, with an average (Standard Deviation [SD]) baseline SDMT score of 53.1 (10.7). 75.1% of patients were female, and average (SD) age was 42.3 (10.8) years. Average (SD) EDSS at time of baseline SDMT score was 1.7 (1.6). When adjusted for age, sex, and baseline EDSS, an increase in baseline SDMT score by 10 points (i.e., better CPS) was associated with lower risk of progression to EDSS 3.0 (adjusted HR=0.75 (95% CI: 0.64, 0.87); p<0.001), 4.0 (adjusted HR=0.81 (0.65, 0.99); p=0.044), and 7.0 (adjusted HR=0.67 (0.50, 0.89); p=0.006).

Conclusions:

In this study CPS predicted disability milestones in PlwMS and could be used by clinicians as a prognostic tool to inform earlier therapeutic intervention, which in turn may delay long-term disability accrual.