Longitudinal Evaluation of Cognition in Multiple Sclerosis: Impact of Cognitive Reserve

Background: Up to 70% of people with multiple sclerosis (PwMS) suffer cognitive impairment in multiple domains, including complex attention, information processing speed, learning and memory, and executive function. Cognitive outcomes in PwMS, however, are highly variable. For instance, some PwMS remain cognitively intact despite advanced disease. Cognitive reserve (CR) theory postulates that individuals with higher levels of intellectual enrichment can tolerate more pathology than others before exhibiting cognitive impairment. The North American Adult Reading Test (NAART), which measures a person’s ability to pronounce phonetically irregular words, estimates the verbal intellectual abilities of individuals who have acquired cognitive dysfunction. CR can be quantified using NAART and years of education as proxy measures.

Objectives: The current study evaluated whether or not PwMS were impaired compared to healthy controls (HC) on measures of cognitive functioning across several domains.  This study also investigated whether CR predicted cognitive outcome following a three-year interval.

Methods: Thirty-two individuals with early-phase relapsing-remitting MS were recruited from the MS Clinic of the Ottawa Hospital. All had a mild level of physical disability and a disease duration of less than 10 years. In addition, 32 age, education, and IQ-matched healthy controls were recruited from the community. At both baseline and after a three-year interval participants completed an extensive battery of neuropsychological tests which evaluated a variety of cognitive domains (ex. information processing speed, visual/verbal memory, etc.). CR was assessed using individuals’ education (in years), and their score on the NAART.

Results: On tasks targeting information processing speed, memory, and executive functions, PwMS did worse than HC. On memory and language tasks there was no significant difference between PwMS and HC. CR measures, specifically years of education and NAART scores, did not predict follow-up scores in any cognitive domain.

Conclusions: These results suggest that PwMS show less cognitive impairment in some cognitive domains compared to others  in the early-phase of the disease. Secondly, results indicate that CR did not predict cognitive outcome in the early phase of the disease in this sample.  Results were discussed in terms of unique characteristics of our sample.