Sensory-Motor and Affective-Fatigue Factors are Associated with Symbol Digit Performance in Multiple Sclerosis

Abstract

Objectives: The oral Symbol Digit Modalities Test (SDMT) has become the standard for the brief screening of cognitive impairment in persons with multiple sclerosis (PwMS). It has been shown to be sensitive to sensory-motor factors involving rudimentary oral motor speed and visual acuity, as well as multiple sclerosis (MS) affective-fatigue factors including depression, fatigue, and anxiety. The present study was designed to provide a greater understanding of these noncognitive factors that might contribute to the oral SDMT by examining all these variables in the same sample. Methods: We examined 50 PwMS and 49 healthy controls (HCs). All participants were administered the oral SDMT, two sensory-motor tasks (visual acuity and oral motor speed), and three affective-fatigue measures (depression, fatigue, and anxiety). Results: Partially consistent with hypotheses, we found that sensory-motor skills, but not affective-fatigue factors, accounted for some of the group differences between the MS and HC groups on the oral SDMT, reducing the MS/HC group variance predicted from 10% to 4%. Also, PwMS with below average sensory-motor abilities had oral SDMT scores that were lower than PwMS with intact sensory-motor skills (p