In recent years, a few studies found correlations between processing speed and physical disability in patients with multiple sclerosis (pwMS). However, it remains unclear if this specific cognitive subdomain improves prediction of physical impairment in pwMS.
The aim of this study was to investigate, if cognitive performance at baseline improves prediction of physical impairment at follow-up, controlling for demographics, clinical and MRI data.
We investigated pwMS who had undergone clinical, cognitive and MRI assessment at two timepoints (baseline and follow-up). Physical impairment was measured using the Expanded Disability Status Scale (EDSS) and was defined by an EDSS-Score above 3.0. Cognitive performance was assessed by the Z-score of the Symbol Digit Modality Test (SDMT), measuring processing speed.
109 pwMS took part at baseline (70 female; 34 clinically isolated syndrome (CIS), 64 relapsing-remitting MS (RRMS), 8 secondary-progressive MS (SPMS), 1 SPMS with relapses, 2 primary-progressive MS (PPMS)) and follow-up assessment (20 CIS, 70 RRMS, 14 SPMS, 3 SPMS with relapses, 2 PPMS). Their mean age at baseline was 36 years (10 SD) and the mean follow-up duration was seven years (3.8 SD). At baseline, MS patients had a mean SDMT Z-score of -1.16 (1.19 SD). The median EDSS at baseline and follow-up was 2.0 (range 0 - 8). A binary-logistic regression (Nagelkerke R2= .560, p < 0.001) that included age, disease duration, clinical phenotype, baseline physical impairment, cognitive performance, lesion load and normalized gray matter volume at baseline showed that processing speed (OR: 0.392, p = .007) and age (OR: 1.094, p = .035) at baseline were the only significant independent predictors of physical impairment at follow-up. MRI data at baseline correlated with EDSS at FU, but did not add to this prediction.
Processing speed at baseline independently improved prediction of physical impairment in pwMS after seven years. This highlights the importance of cognitive assessment in addition to the rating of physical impairment. In future, neuropsychological examination could further support determination of the degree of disability in pwMS.