Assessment of Cognitive Function and Fatigue in Multiple Sclerosis

Multiple Sclerosis is an inflammatory, chronic demyelinating disease that affects the central nervous system. It's resulting lesions can incur in progressive fatigue and cognitive function impairment, severely impacting quality of life and economic burden of disease, independently of physical disability. Almost half of patients defined as NEDA-3 had deterioration in at least 2 cognitive domains in a 2-year follow-up. The study’s aim was to compare the Symbol Digit Modalities Test (SDMT) and the Modified Fatigue Impact Scale (MFIS) results when applied to patients with Multiple Sclerosis, and determine if a higher fatigue impacted the performance in cognitive function evaluation. The SDMT is a neuropsychological tool to assess sustained attention and information processing speed, two cognitive domains commonly impaired in Multiple Sclerosis, with a lower score indicating worse performance and more impairment. Conversely, the MFIS is an instrument to measure the subjective experience of fatigue, such that a higher score indicates larger impact, and was used in place of the 40 items long Fatigue Impact Scale to avoid unnecessary patient fatigue without skewing the results. Participants were elected from general population from the city of São Paulo, Brazil, and had a previous diagnosis of Multiple Sclerosis. They were instructed on how to adequately fill the MFIS, and upon finishing, the SDMT was applied by a trained researcher. Results were then compiled in a spreadsheet and compared via Pearson’s R of each test result’s z-score. Test results were Pearson’s R = -0.273 when correlating the SDMT and MFIS z-scores, with a p=0.007, indicating a statistically significant negative correlation between SDMT and MFIS. The results allow us to infer that, indeed, patients with Multiple Sclerosis suffering from fatigue perform worse in cognitive demanding tasks.