Patterning Chronic Active Demyelination in Slowly Expanding/Evolving White Matter MS Lesions

Background and purpose: Slowly expanding/evolving lesions measured by conventional T1-weighted/T2-weighted brain MR imaging may contribute to progressive disability accumulation in MS. We evaluated the longitudinal change in myelin and axonal tissue integrity in white matter slowly expanding/evolving lesions by means of the magnetization transfer ratio and DTI radial diffusivity.

Materials and methods: Slowly expanding/evolving lesions were detected within the Study to Assess the Efficacy, Safety, Tolerability, and Pharmacokinetics of BIIB033 in Participants With Relapsing Forms of Multiple Sclerosis When Used Concurrently With Avonex (SYNERGY) Phase 2 clinical trial dataset (NCT01864148), comprising patients with relapsing-remitting and secondary-progressive MS (n = 299) with T1-weighted/T2-weighted MR imaging at all trial time points (baseline to week 72).

Results: Compared with non-slowly expanding/evolving lesions (areas not classified as slowly expanding/evolving lesion) of baseline nonenhancing T2 lesions, slowly expanding/evolving lesions had a lower normalized magnetization transfer ratio and greater DTI radial diffusivity, both in patients with relapsing-remitting MS (n = 242) and secondary-progressive MS (n = 57, P < .001 for all). Although the changes with time in both the normalized magnetization transfer ratio and DTI radial diffusivity between slowly expanding/evolving lesions and non-slowly expanding/evolving lesions were positively correlated (P < .001), a decrease in the normalized magnetization transfer ratio and a greater increase in DTI radial diffusivity were observed in slowly expanding/evolving lesions versus non-slowly expanding/evolving lesions from baseline to week 72 in relapsing-remitting MS and secondary-progressive MS (P < .001 for all).

Conclusions: Patterns of longitudinal change in the normalized magnetization transfer ratio and DTI radial diffusivity in slowly expanding/evolving lesions were consistent with progressive demyelination and tissue loss, as seen in smoldering white matter MS plaques.