Abstract
ObjectivesOver 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.MethodsWe examined disease progression and demographics over two decades and assessed the effect of disease-modifying therapies using linear mixed-effect models.ResultsIn 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 disease-modifying 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.ConclusionThe 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.
Highlights
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]
In the prevalent MS population of Buskerud and Telemark (BT)-living, 1070 patients were alive and residing in these two counties on date of prevalence, which corresponds to a crude prevalence of 235.1/100 000
The prevalence adjusted to the European standard population was 237.4/100 000
Summary
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 disease-modifying treatments (DMTs) [2, 4, 5]. Recent studies are usually based on large, multicenter databases such as MSBase [11] and national MS registries [12], which rarely represent a complete population [13]. The translatability of these studies to the general MS population is under scrutiny [14]. The aim of this study is to investigate changes in the natural course of MS over time in a complete and geographically well-defined population
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