Background: Diffusion magnetic resonance imaging can reveal quantitative information about the tissue changes in multiple sclerosis. The recently developed multi-compartment spherical mean technique can map different microscopic properties based only on local diffusion signals, and it may provide specific information on the underlying microstructural modifications that arise in multiple sclerosis.
Objective: Given that the lesions in multiple sclerosis may reflect different degrees of damage, we hypothesized that quantitative diffusion maps may help characterize the severity of lesions “in vivo” and correlate these to an individual’s clinical profile.
Methods: We evaluated a cohort of 59 MS patients (62% female, mean age 44.7 years), for whom demographic and disease information was obtained, and who underwent a comprehensive physical and cognitive evaluation. MRI protocol included conventional sequences to define focal lesions and multi-shell diffusion imaging. Quantitative diffusion properties were used to discriminate distinct types of lesions through a k-means clustering algorithm, and the number and volume of those lesions were correlated with parameters of the disease.
Results: The combination of microscopic and macroscopic diffusion properties differentiated two types of lesions, with a prediction strength of 0.931. The type B lesions had larger diffusion changes compared to the type A lesions, irrespective of their location (P <0.001). The number and volume of type B lesions was related to the severity of disease evolution, clinical disability and cognitive decline (P =0.004, Bonferroni correction). Specifically, more and larger type B lesions were correlated with a worse Multiple Sclerosis Severity Score, cerebellar function and cognitive performance, and a greater need for high-efficacy treatments.
Conclusions: The severity of damage within focal lesions have the potential to permit more specific understanding of the mechanisms that drive disease evolution.