Relevance of cognitive deterioration in early relapsing-remitting MS: a 3-year follow-up study

Objective: To assess longitudinally cognitive functioning in relapsing-remitting multiple sclerosis (RRMS) patients and its relationship with clinical and MRI variables. Methods: Early RRMS patients and matched healthy controls were assessed in parallel in three testing sessions over 3 years, using the Rao's Brief Repeatable Battery of Neuropsychological Tests. Patients also underwent an MRI analysis of T2-weighted lesion volume (T2LV), number of gadolinium-enhanced lesions and whole brain atrophy. Forty-nine RRMS patients (mean age 36.9 +/- 8.9 years; mean disease duration 2.9 +/- 1.7 years, mean Expanded Disability Status Scale, 1.7 +/- 0.7) and 56 healthy controls were recruited. Results: At baseline, cognitive impairment was detected in 15 patients (30.6%). After 3 years, cognitive functioning worsened in the 29.3% of patients, whereas Expanded Disability Status Scale progression was observed in only three patients. The most sensitive test to detect cognitive deterioration over time was the Symbol Digit Modalities Test (SDMT). Only the presence of moderate cognitive impairment at baseline predicted further cognitive deterioration (p = 0.03). Among MRI variables, T2LV showed a weak to moderate relationship with some cognitive tasks. Conclusions: Over a 3-year period cognitive deterioration can be expected in approximately one-third of MS patients with relatively short disease duration. The SDMT is particularly suitable for longitudinal assessment of MS-related cognitive changes.