Background: The Symbol Digit Modalities Test (SDMT) is most frequently used to test processing speed in patients with multiple sclerosis (MS). Functional imaging studies emphasize the importance of frontal and parietal areas for task performance, but the influence of frontoparietal tracts has not been thoroughly studied. We were interested in tract-specific characteristics and their association with processing speed in MS patients.
Methods: Diffusion tensor imaging was obtained in 100 MS patients and 24 healthy matched controls to compare seed-based tract characteristics descending from the superior parietal lobule [Brodman area 7A (BA7A)], atlas-based tract characteristics from the superior longitudinal fasciculus (SLF), and control tract characteristics from the corticospinal tract (CST) and their respective association with ability on the SDMT.
Results: Patients had decreased performance on the SDMT and decreased white matter volume (each p < 0.05). The mean fractional anisotropy (FA) for the BA7A tract and CST ( p < 0.05), but not the SLF, differed between MS patients and controls. Furthermore, only the FA of the SLF was positively associated with SDMT performance even after exclusion of the lesions within the tract ( r = 0.25, p < 0.05). However, only disease disability and total white matter volume were associated with information processing speed in a linear regression model.
Conclusions: Processing speed in MS is associated with the structural integrity of frontoparietal white matter tracts.
Competing Interests: MG received honoraria or speaking fees from Biogen, Celgene, Merck Serono, Novartis, Roche, Sanofi Genzyme, and Teva. IP has received honoraria for speaking at scientific meetings, serving on scientific advisory boards, and consulting activities from Adamas Pharma, Almirall, Bayer Pharma, Biogen, BMS, Celgene, Desitin, Sanofi-Genzyme, Janssen, Merck, Novartis, Roche, and Teva. She has also received research support from the German MS Society, Celgene, Novartis, Roche, and Teva. ML is a paid editor for the Thieme Verlag. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
(Copyright © 2022 Grothe, Jochem, Strauss, Langner, Kirsch, Hoffeld, Penner, Nagels, Klepzig, Domin and Lotze.)