Multiple sclerosis (MS) is primarily a demyelinating disease of the central nervous system (CNS), but many patients also undergo progressive atrophy, especially in the gray matter (GM). GM atrophy plays a particularly prominent role in development of cognitive and physical disability in MS. Evidence is mounting that there is a profound infiltration of activated microglia and blood-borne macrophages throughout the lesions, whereas in slowly expanding (smoldering) or chronic active expanding lesions, the microglia and macrophages are concentrated as a dense rim around the lesions. Microglia is also activated, in a more diffuse way, in the white matter (WM) and GM with concomitant axonal degeneration and meningeal inflammation. Thus, chronic activation of microglia has been linked to neurodegeneration in the progressive phase of the disease and development of brain atrophy.~No longitudinal studies in MS examined the association between development of microglia-related pathology in patients treated with siponimod (Mayzent®). This will be the first study to examine the treatment effect of Mayzent on microglia in MS.
To assess the efficacy of Mayzent on microglia pathology in patients with active SPMS, as compared to the active control group of MS patients treated with the Ocrevus, as measured by changes in microglial activation in the lesional and non-lesional NAWM and NAGM and in the peri-plaque area of chronic lesions in the brain.