Cognitive patterns and progression in multiple sclerosis: construction and validation of percentile curves

Background and objectives: Rate and pattern of progression of cognitive decline in multiple sclerosis (MS) has not been clearly identified. The present study aimed to identify correlations between cognitive tests and disease duration, construct longitudinal cognitive curves, and assess pattern of change over time. Methods: The Neuropsychological Screening Battery for Multiple Sclerosis was administered in 150 consecutive MS patients, and tests that correlated with disease duration were identified. Percentile curves were constructed and the pattern of cognitive decline over time explored. The cognitive curves were validated in an additional group of 83 patients with MS. Results: Three of four measures of the spatial recall test (SPART 7/24), and the paced auditory serial addition task for two seconds (PASAT 29), correlated with disease duration. These tests were used to construct cross-sectional curves identifying the pattern of cognitive decline over time in the MS population. On the basis of this cross-sectional analysis, the earliest cognitive decline occurred in the SPART 7/24 trials 1-5 between one and three years from onset, followed by decline in the SPART delayed recall between three and seven years, and then by decline in the PASAT 29 after seven years from onset. Conclusions: Verbal fluency and verbal memory appear to be affected earliest in MS. The pattern of cognitive decline is further characterised by a decrease in visuospatial learning, followed by delayed recall, and then by attention and information processing speed. Cognitive percentile curves can be used to evaluate the pattern of progression and identify patients at increased risk.