The Relationship between Intra-Individual Cognitive Variability, Cognitive Status, and Motor Function in Individuals with Multiple Sclerosis
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Deficits in motor and cognitive functioning are prevalent in individuals with MS. Past research has demonstrated that mobility is significantly impacted by cognitive impairment. The presence of cognitive impairment is typically assessed through neuropsychological assessments; however, performances on specific tests are compared to normative samples, which do not adjust for inconsistency in an individual's performance. Past research indicated that intra-individual across-neuropsychological test variability is predictive of incident dementia and associated with poor cognitive function in healthy older adults. To our knowledge, no study to date has assessed intra-individual across-neuropsychological test variability as it relates to cognitive status or motor function in MS. The primary aims of this study are to compare mean level of performance and cognitive variability in predicting cognitive status and to examine the relationships between walking time and cognitive status and cognitive variability and walking time. Results revealed that lower mean level of performance predicted cognitive impairment. The full model was statistically significant, &khgr;2 (4, N = 93) = 68.14,p < .001. Mean level of performance was the only variable that contributed uniquely to the model. Greater cognitive variability also significantly predicted cognitive impairment. The full model was statistically significant, &khgr; 2 (4, N = 93) = 9.78,p = .04. Cognitive variability was the only variable that made a unique statistically significant contribution to the model, recording an odds ratio of 7.10. Cognitive variability did not predict cognitive impairment above and beyond that predicted by mean level of performance. Walking time approached significance (p = .08), while age and disability significantly predicted cognitive status. The full model was statistically significant, &khgr;2 (4, N = 95) = 19.60, p = .001. Lastly, age and level of disability significantly predicted walking time, with the disability score recording a higher beta value (b = .38, p < .001) than age (b = .26, p = .004), while cognitive variability and gender did not. Overall, this study highlights the importance of routine cognitive and motor assessments and the potential value of considering cognitive variability in addition to standard scoring procedures when assessing cognitive and motor functioning in individuals with MS.