Background: The accrual of brain focal pathology is considered a good substrate of disability in relapsing-remitting multiple sclerosis (RRMS). However, knowledge on long-term lesion evolution and its relationship with disability progression is poor.

Objective: The objective of this paper is to evaluate in RRMS the long-term clinical relevance of brain lesion evolution.

Methods: In 58 RRMS patients we acquired, using the same scanner and protocol, brain magnetic resonance imaging (MRI) at baseline and 10±0.5 years later. MRI data were correlated with disability changes as measured by the Expanded Disability Status Scale (EDSS).

Results: The annualized 10-year lesion volume (LV) growth was +0.25±0.5 cm(3) (+6.7±8.7%) for T2-weighted (T2-W) lesions and +0.20±0.31 cm(3) (+11.5±12.3%) for T1-weighted (T1-W) lesions. The univariate analysis showed moderate correlations between baseline MRI measures and EDSS at 10 years (p < 0.001). Also, 10-year EDSS worsening correlated with LV growth and the number of new/enlarging lesions measured over the same period (p < 0.005). In the stepwise multiple regression analysis, EDSS worsening over 10 years was best correlated with the combination of baseline T1-W lesion count and increasing T1-W LV (R = 0.61, p < 0.001).

Conclusions: In RRMS patients, long-term brain lesion accrual is associated with worsening in clinical disability. This is particularly true for hypointense, destructive lesions.