The ectopic lymphoid follicles are composed of B-cells, T follicular helper cells and follicular dendritic cells. Rituximab is a monoclonal antibody against CD-20 (a B-cell marker) that is FDA approved for the treatment of various lymphomas. It has been shown to be effective when given intravenously in trials of Relapsing-Remitting Multiple Sclerosis (RRMS). However, the cerebrospinal fluid (CSF) penetrance of rituximab is minimal, such that CSF levels are < 1% of serum levels after the administration of intravenous (IV) rituximab. Indeed, IV rituximab failed to significantly slow disability in a clinical trial in progressive MS. Intrathecal (IT) rituximab administration has been used in CNS lymphoma to achieve greater CSF concentrations of rituximab. In MS, IT administration of rituximab could lead to higher CSF rituximab levels resulting in the disruption of meningeal ectopic lymphoid follicles, ultimately reducing cortical lesions and possibly disease progression.