Cognitive dysfunction characteristics of multiple sclerosis with aging

Background We aimed to investigate the characteristics of cognitive impairment in older people with multiple sclerosis (MS). Methods Cross-sectional study that included participants that were examined with a common and comprehensive neuropsychological protocol. The subjects were matched by sociodemographic variables and the following groups were generated for comparisons: young MS versus healthy controls (HC) (n=246), old MS versus HC (n=198), young MS vs old MS (n=226), MS vs Alzheimer's disease (AD)(n=70), and MS vs Parkinson's disease (PD) (n=62). The IC-CoDiMS criteria were used to define cognitive impairment in MS. Results Cognitive impairment was more frequent in young than old patients (70.8% vs 52.2%). Attention and speed processing is the most frequent cognitive domain impaired in MS (54.9% of young MS vs 32.7% of old MS). The frequency of impairment in attention/processing speed (54.9% vs 32.7%) and episodic memory (27.9% vs 14.3) was higher in the young group than in the old group. There were no statistically significant differences in the distribution of impairment in executive function (46.0% vs 35.3%), visuospatial (17.9% vs 9.5%), and language (12.4% vs 17.7%). In those patients meeting the criteria for cognitive impairment, young MS patients showed lower performance in attention/processing speed tests. Conversely, old MS patients showed lower performance in episodic memory, verbal fluency, and planning. There were no differences in the correlations between SDMT and other neuropsychological tests in young and old patients, which suggests similar cognitive processes underlying SDMT performance in both groups. There were differences between old MS and prodromal AD, especially in episodic memory, while the cognitive profile of old MS was largely shared with PD. Conclusions Our study found that the cognitive profile of MS is defined by a characteristic impairment in attention and processing speed, which is present during the lifespan. The impairment in processing speed is less prominent in old age, whereas the impairment of other cognitive functions becomes more relevant. These findings suggest potential differences in the pathophysiological processes associated with cognitive impairment between young and old ages that warrant further investigation.