Abstract
Cognitive impairment is a common complaint in people with multiple sclerosis (pwMS). The study objective was to determine the psychometric properties of the letter digit substitution test (LDST) that measures information processing speed and to investigate the impact of relevant predictors of LDST achievement in pwMS. The design was cross-sectional. The study included 87 pwMS and 154 control subjects. The validity of LDST was examined, and a hierarchical regression model was used to explore relevant predictors of LDST success. The LDST had excellent construct validity, as expressed by differences between pwMS and control subjects. Convergent validity of the LDST was supported by a significant moderate correlation with the expanded disability status scale (EDSS) (ρ = −0.36; p < 0.05) and a significantly strong correlation with the multiple sclerosis impact scale (MSIS-29) physical subscale (r = −0.64; p < 0.01). The LDTS score well differentiated the pwMS considering age, education, EDSS, disease duration, comorbidity, and medication therapy. Using the LDST as a criterion variable in pwMS results showed consistent evidence for the age, education, and EDSS impact on LDST performance. The best cut-off score of ≤35 discriminated the control and MS group. LDST proved to be a valid test for assessing information processing speed in pwMS.
Highlights
Multiple sclerosis (MS) is a chronic inflammatory neurological disease of the central nervous system with autoimmune etiology leading to a broad and complex clinical picture affecting 2–144 per 100,000 people in Japan, America, and Europe [1]
In the Croatian clinical setting of people with multiple sclerosis (pwMS), two tests are randomly used for assessing information processing speed, SDMT [5] and the letter digit substitution test (LDST) [6,7], an adaptation of earlier substitution tests, the digit symbol substitution test (DSST) [8], and the SDMT [5,9]
We aimed to evaluate the psychometric properties of the LDST [6,7] in terms of validity and reliability in a Croatian sample of pwMS and including a non-clinical sample
Summary
Multiple sclerosis (MS) is a chronic inflammatory neurological disease of the central nervous system with autoimmune etiology leading to a broad and complex clinical picture affecting 2–144 per 100,000 people in Japan, America, and Europe [1]. The impairment associated with information processing is the first cognitive deficit to emerge in pwMS [4]. Information processing speed is frequently assessed via the symbol/digit substitution test (the participant is instructed to associate symbols to letters (or vice versa) or compare symbols and provide an oral or written response (e.g., symbol digit modalities test (SDMT)) [5]. In the Croatian clinical setting of pwMS, two tests are randomly used for assessing information processing speed, SDMT [5] and the letter digit substitution test (LDST) [6,7], an adaptation of earlier substitution tests, the digit symbol substitution test (DSST) [8], and the SDMT [5,9]
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