Repeated forms, testing intervals, and SDMT performance in a large multiple sclerosis dataset

Tom A Fuchs; John Gillies; Michael G Jaworski 3rd; Gregory E Wilding; Margaret Youngs; Bianca Weinstock-Guttman; Ralph Hb Benedict

doi:10.1016/j.msard.2022.104375

Repeated forms, testing intervals, and SDMT performance in a large multiple sclerosis dataset

Mult Scler Relat Disord. 2022 Dec:68:104375. doi: 10.1016/j.msard.2022.104375. Epub 2022 Oct 30.

Authors

Tom A Fuchs¹, John Gillies², Michael G Jaworski 3rd², Gregory E Wilding³, Margaret Youngs², Bianca Weinstock-Guttman², Ralph Hb Benedict⁴

Affiliations

¹ Jacobs Multiple Sclerosis Center, Department of Neurology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, 1001 Main Street, Buffalo, NY 14203, United States of America; Buffalo Neuroimaging Analysis Center, Department of Neurology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, NY, United States of America.
² Jacobs Multiple Sclerosis Center, Department of Neurology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, 1001 Main Street, Buffalo, NY 14203, United States of America.
³ Department of Biostatistics, University at Buffalo, The State University of New York, Buffalo, NY, United States of America.
⁴ Jacobs Multiple Sclerosis Center, Department of Neurology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, 1001 Main Street, Buffalo, NY 14203, United States of America. Electronic address: benedict@buffalo.edu.

PMID: 36544304
DOI: 10.1016/j.msard.2022.104375

Abstract

Background: The Symbol Digit Modalities Test (SDMT), the most reliable and sensitive measure of cognition in people with multiple sclerosis (PwMS), is increasingly used in clinical trials and care.

Objectives: We aimed to establish how SDMT performance is influenced by repeating forms and frequency of use in PwMS.

Methods: A retrospective analysis was completed on a large database of PwMS (n = 740) with multiple SDMT administrations. Change in SDMT performance was analyzed, accounting for frequency of tests and utilization of alternate- versus same-form conditions.

Results: SDMT administrations ranged from 2 to 14 per subject over a mean (SD) of 5.9 (4.5) years. Accounting for demographics, the mixed effects model revealed a significant main effect of SDMT exposures (1.8 point improvement per repetition, p = 0.001) and an interaction between time since previous SDMT and whether the same test form was administered in the previous administration (estimate=-1.1, p = 0.037). As well, SDMT decline is observed when testing intervals exceed two years (F = 9.69, p<0.001).

Conclusion: Improvements in SDMT performance with repeated exposure, likely reflecting practice effects, were greatest when repeating the same SDMT form over briefer intervals. We recommend the use of alternate forms or analogous versions of timed symbol-digit coding particularly where samples are saturated with many administrations.

Keywords: Cognition; Multiple sclerosis; Practice effects; Processing speed; SDMT.

MeSH terms

Cognition
Cognition Disorders*
Humans
Multiple Sclerosis* / diagnosis
Neuropsychological Tests
Retrospective Studies