Risk factors associated with the onset of relapsing-remitting and primary progressive multiple sclerosis: a systematic review.

Kyla A Mckay,Helen Tremlett,Vivian Kwan,Thomas Duggan

doi:10.1155/2015/817238

Abstract

Multiple sclerosis (MS) is a chronic central nervous system disease with a highly heterogeneous course. The aetiology of MS is not well understood but is likely a combination of both genetic and environmental factors. Approximately 85% of patients present with relapsing-remitting MS (RRMS), while 10–15% present with primary progressive MS (PPMS). PPMS is associated with an older onset age, a different sex ratio, and a considerably more rapid disease progression relative to RRMS. We systematically reviewed the literature to identify modifiable risk factors that may be associated with these different clinical courses. We performed a search of six databases and integrated twenty observational studies into a descriptive review. Exposure to Epstein-Barr virus (EBV) appeared to increase the risk of RRMS, but its association with PPMS was less clear. Other infections, such as human herpesvirus-6 and chlamydia pneumoniae, were not consistently associated with a specific disease course nor was cigarette smoking. Despite the vast literature examining risk factors for the development of MS, relatively few studies reported findings by disease course. This review exposes a gap in our understanding of the risk factors associated with the onset of PPMS, our current knowledge being predominated by relapsing-onset MS.

Highlights

Multiple sclerosis (MS) is a chronic central nervous system disease, characterized by demyelination and axonal loss
We systematically reviewed the literature on risk factors for the development of relapsing-onset and primary progressive MS, with a focus on modifiable factors
The vast majority (18/20) of articles reported on risk factors for relapsingonset MS, and just over half (12/20) examined risk factors associated with progressive-onset MS, a high proportion (5/12) was only able to compare the risk relative to relapsing-onset MS

Summary

Introduction

Multiple sclerosis (MS) is a chronic central nervous system disease, characterized by demyelination and axonal loss. These physiological irregularities translate into significant clinical disability. 85% of patients present with a relapsingremitting course (RRMS), which is characterized by episodes of acute worsening of function followed by partial or complete recovery [4]. RRMS onset typically occurs in early adulthood, and, within around two decades, approximately half will go on to develop secondary progressive MS (SPMS) [5]. SPMS is defined as a steady clinical deterioration, independent of relapses [6]. The median age of onset is 40 years for progressive-onset (PPMS) and 30 years for relapsing-onset MS (RRMS/SPMS), a difference of ten years [7]. A higher female preponderance is consistently seen in relapsing-onset but not in progressive-onset MS [8]

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