MRI studies have consistently shown structural and functional alterations in the brain of patients with MS. However, pathogenic mechanisms of MS are “multidimensional”, reflecting complex events and thus requiring multivariate analysis methods. A complementary knowledge of such events and their clinical relevance is currently lacking in MS.
To investigate “hidden” covarying structural-functional pathogenic patterns in MS patients compared to normal controls (NC).
We applied linked independent component analysis, a type of fusion approach, to images of grey matter (GM) density, fractional anisotropy (FA) and resting-state functional MRI. We assessed 100 relapsing-remitting MS patients (age: 39.7±10.5 years, 60 female, disease duration: 9.4±6.9 years; median EDSS=1.5, cognitive impairment [CI]: 30%) and 43 demographically-matched NC.
Out of 20 linked structural-functional patterns across study population, only one showed significant group difference, with a loading coefficient across MRI modalities lower in MS than NC (-0.29±1.05 vs 0.69±0.34, corrected-p <0.004), which was already present at very early disease stage and was particularly low in the MS subgroups with larger white matter (WM) lesion volume (LV, >3.5 cm3), higher EDSS (>1.5), CI occurrence and longer disease duration (>5 years). The contribution of each modality to the significant linked covarying pattern was 41% for GM density, 42% for WM FA and 17% for network-functional connectivity (FC). The contribution of FC increased in the MS group with increasing LV, EDSS, CI and disease duration.
These findings suggest that in MS patients with mild disability common pathogenic mechanisms are characterized by a prevalent structural damage equally affecting WM and GM and, to a lesser degree, by concurrent widespread alteration of short-range FC. Such mechanism is already present since the early MS stage and becomes more pronounced with increasing focal pathology and disease severity.