Cognitive processing speed in multiple sclerosis clinical practice: association with patient-reported outcomes, employment, and MRI metrics.

OBJECTIVE: To analyze the relationship between cognitive processing speed, patient-reported outcome measures (PROMs), employment, and MRI metrics in a large multiple sclerosis cohort METHODS: Cross-sectional clinical data, PROMs, employment, and MRI studies within 90 days of completion of the Processing Speed Test (PST), a technology-enabled adaptation of the Symbol Digit Modalities Test, were collected. MRIs were analyzed using semi-automated methods. Correlations of PST with PROMs and MRI metrics were examined using Spearman's rho. Wilcoxon Rank Sum Testing compared MRI metrics across PST quartiles, and linear regression models identified predictors of PST performance. Effects of employment and depression were also investigated. RESULTS: In 721 patients (mean age 47.6+/-11.4 years), PST scores were significantly correlated with all MRI metrics, including cord atrophy and deep grey matter volumes. Linear regression demonstrated self-reported physical disability, cognitive function, fatigue and social domains (Adjusted R(2) =0.44, p-value<0.001) as the strongest clinical predictors of PST, whereas that of MRI variables included T2 lesion volume, whole brain fraction, and cord atrophy (Adjusted R(2) =0.42, p-value<0.001). An inclusive model identified T2 lesion volume, whole brain fraction, self-reported upper extremity function, cognition and social participation as the strongest predictors of PST (Adjusted R(2) =0.51, p-value<0.001). There was significant effect modification by depression on the relationship between self-reported cognition and PST performance. Employment status was associated with PST scores independent of age and physical disability. INTERPRETATION: The PST correlates with PROMs, MRI measures of focal and diffuse brain injury, and employment. The PST is a feasible and meaningful measure for routine multiple sclerosis care.