Multiple sclerosis (MS) is a chronic inflammatory disorder affecting the central nervous system that is characterized pathologically by focal demyelinating lesions in the brain parenchyma. Meningeal inflammation in MS was first noted in 2004. Ectopic lymphoid follicles were described in the meninges of patients with secondary progressive MS (SPMS) and were thought to correlate with cortical lesions and atrophy (a surrogate marker for disability). Subsequently, inflammation in the meninges has been described in primary progressive MS (PPMS) as well as early relapsing MS.