Cerebellar subregional atrophy in relapsing-remitting multiple sclerosis: Stage-dependent dynamics and...

Cerebellar atrophy is increasingly recognized as an important pathological feature of multiple sclerosis (MS). However, the specific patterns at different stages and their alteration by disease-modifying therapies (DMTs) are not well comprehended.

This study aimed to investigate stage-dependent cerebellar subregional volume changes in relapsing-remitting MS (RRMS) and evaluate the effects of different DMT classes on cerebellar atrophy and clinical outcomes.

A total of 181 patients with RRMS and 99 healthy controls were recruited for this study. Patients were stratified by lesion activity into acute-active, chronic-active, and chronic-inactive subgroups, and by pharmacological mechanism into untreated, sphingosine-1-phosphate (S1P)_T (siponimod, fingolimod, and ozanimod) and not_S1P_DMT (dimethyl fumarate and teriflunomide). Cerebellar subregional volumes were quantified using the deep learning-based tool, CerebNet. Group comparisons were conducted, and interaction effects were examined. The correlations between the cerebellar subregions and cognition were subsequently analyzed.

In the lesion-activity subgroups, significant volume loss was detected in several posterior cerebellar lobules, including Crus II, VIIIa/b, VIIb, X, Crus I, and IX (all p < 0.05). The acute-active subgroup exhibited additional atrophy in anterior lobules I-IV and vermis IX compared with the chronic-active subgroup (all p < 0.05). In the treatment subgroups, widespread reductions were observed in the posterior lobules Crus I/II, V, VIIb, VIIIb, IX, and X, with most decreases appearing in the untreated groups (all p < 0.05). Pairwise comparisons displayed region-specific patterns: left VIIIa volume was reduced in the MS_noDrug and MS_not_S1P_DMT groups but increased in the S1P_DMT group, whereas right lobule V in the S1P_DMT and vermis VI in the MS_not_S1P_DMT were both higher (all p < 0.05). The interaction effects of disease stage and treatment were mainly localized to lobules IX and VIIIb, and the volumes of bilateral IX lobules showed a weak positive correlated with cognitive performance.

This study demonstrated stage-specific patterns of cerebellar atrophy in RRMS and the heterogeneous, stage-dependent effects of DMTs on posterior cerebellar subregions. Lobules IX and VIIIb emerged as critical loci linking pharmacological modulation with cognitive outcomes. These findings suggest that these regions may serve as potential imaging biomarkers of therapeutic response and prognosis in MS.