The course of multiple sclerosis rewritten: a Norwegian population-based study on disease demographics and progression
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ORIGINAL COMMUNICATION
The course of multiple sclerosis rewritten: a Norwegian population‑based study on disease demographics and progression Cecilia Smith Simonsen1,3,4 · Heidi Øyen Flemmen2,5 · Line Broch1,3,4 · Cathrine Brunborg6 · Pål Berg‑Hansen3 · Stine Marit Moen7 · Elisabeth Gulowsen Celius3,4 Received: 3 August 2020 / Revised: 13 October 2020 / Accepted: 14 October 2020 © The Author(s) 2020
Abstract Objectives Over the past few decades, there has been an improvement in the rate of disability progression in multiple sclerosis (MS) patients, and most studies relate this evolvement to the introduction of disease-modifying therapies. However, several other factors have changed over this period, including access to MRI and newer diagnostic criteria. The aim of this study is to investigate changes in the natural course of MS over time in a near-complete and geographically well-defined population from the south-east of Norway. Methods We examined disease progression and demographics over two decades and assessed the effect of disease-modifying therapies using linear mixed-effect models. Results In a cohort of 2097 patients, we found a significant improvement in disability as measured by the Expanded Disability Status Scale (EDSS) stratified by age, and the improvement remained significant after adjusting for time on diseasemodifying medications, gender and progressive MS at onset. The time from disease onset to EDSS 6 in the total cohort was 29.8 years (95% CI 28.5–31.1) and was significantly longer in patients diagnosed after 2006 compared to patients diagnosed before. There are significant differences between patient demographics, as well as time to EDSS 6, in the near-complete, geographically well-defined population compared to an additional cohort from the capital Oslo and its suburbs. Conclusion The natural course of MS is improving, but the improvement seen in disease progression has multifaceted explanations. Our study underlines the importance of completeness of data, relevant timeframes and demographics when comparing different MS populations. Studies on incomplete populations should be interpreted with caution. Keywords Multiple sclerosis · Disease course · Natural history · Epidemiology · Time to EDSS 6
Introduction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00415-020-10279-7) contains supplementary material, which is available to authorized users. * Cecilia Smith Simonsen [email protected] 1
Department of Neurology, Vestre Viken Hospital Trust, Dronninggata, 3004 Drammen, Norway
2
Department of Neurology, Hospital Telemark HF, Skien, Oslo, Norway
3
Department of Neurology, Oslo University Hospital, Oslo, Norway
In 1989, the median time from onset of multiple sclerosis (MS) to dependence on a walking aid, Expanded Disability Status Scale (EDSS) 6, was 15 years [1]. Several studies have confirmed a delay in the time to reach EDSS 6 over the past two decades [2, 3]. Most studies attribute this delay to the effects of di
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