Introduction

Abstract

Since the earliest clinical studies of multiple sclerosis (MS), it has been recognized that a subgroup of patients follows a pattern of disease evolution which is progressive from onset and, as a consequence, has been termed “primary progressive” (PP). Although only 10%–15% of the overall MS patient population is affected by PPMS, this condition on the one hand poses intriguing questions about the nature of the pathophysiological mechanisms underlying the progressive accumulation of neurological disability, and on the other represents an important clinical challenge.