The multiple sclerosis prodrome: Emerging evidence, challenges, and opportunities.

A prodrome is considered an early set of signs or symptoms indicating the onset of a disease or illness. In multiple sclerosis (MS), the prodromal period is the months or years before our current, classic understanding of "MS symptom onset." Prodromal periods are well recognized in other neurodegenerative conditions and more recently have been shown in MS. In this Viewpoint, we reflect on the emerging evidence surrounding the MS prodrome, including features that may be common across chronic inflammatory and neurodegenerative diseases. Finally, we discuss the implications for future disease prevention in MS.