Background In relapsing-remitting multiple sclerosis (RRMS), cortical grey matter pathology relevantly contributes to long-term disability. Still, diffuse cortical inflammation cannot be detected with conventional MRI.

Objective We aimed to assess microstructural damage of cortical grey matter over time and the relation to clinical disability as well as relapse activity in patients with RRMS using multiparametric quantitative (q)MRI techniques.

Methods On 40 patients with RRMS and 33 age-matched and sex-matched healthy controls, quantitative T1, T2, T2* and proton density (PD) mapping was performed at baseline and follow-up after 2 years. Cortical qMRI parameter values were extracted with the FreeSurfer software using a surface-based approach. QMRI parameters, cortical thickness and white matter lesion (WML) load, as well as Expanded Disability Status Scale (EDSS) and relapse rate, were compared between time points.

Results Over 2 years, significant increases of T1 (p≤0.001), PD (p≤0.001) and T2 (p=0.005) values were found in the patient, but not in the control group. At decreased relapse rate over time (p=0.001), cortical thickness, WML volume and EDSS remained unchanged.

Conclusion Despite clinical stability, cortical T1, T2 and PD values increased over time, indicating progressive demyelination and increasing water content. These parameters represent promising surrogate parameters of diffuse cortical inflammation in RRMS.