Time trends in the incidence and prevalence of multiple sclerosis in N orway during eight decades

Abstract

Norway has been subjected to numerous epidemiological investigations on the prevalence and incidence of multiple sclerosis (MS), dating back to 1935. The objective of this study was to review the studies on the prevalence and incidence of MS in Norway, provide an update on the prevalence of MS in Norway, and describe the time trends in the prevalence and incidence of MS in relation to risk factors, case ascertainment, and data. We performed a systematic search on PubMed and MEDLINE up to November 2014 using the search string ‘multiple sclerosis prevalence in Norway’ or ‘multiple sclerosis incidence in Norway’. In addition, we scrutinized the reference lists of the publications identified for relevant citations. We retrieved data on the distribution of MS in Norway on December 31, 2013 from the Norwegian Multiple Sclerosis Registry and Biobank and the Norwegian Patient Registry. We identified 29 articles. From 1961 to 2014, the reported prevalence of MS increased from 20 to 203 per 100,000 inhabitants, and the incidence increased from 1.9 to 8.0 per 100,000. The nationwide crude prevalence in Norway, based on the Norwegian Patient Registry, was 208 per 100,000 on December 31, 2013. The reported prevalence of MS in Norway has increased 10-fold, with several possible causes. During eight decades, neurological health services have generally become more accessible to the population, and transforming diagnostic criteria has made the diagnosis of MS more precise and valid. There have also been changes in lifestyle behavior and known risk factors, such as vitamin D and smoking, that might have contributed to the increased incidence of MS. A possible role of increased survival in MS needs to be examined further.This article is commented on by Berg-Hansen et al, published in 132: 364–367 (DOI: 10.1111/ane.12489).

Multiple sclerosis prevalence in 2000 and 2010 in Western Finland

“…These results point at regional high MS risk in the western coast of Finland. The rates in a large region in Western Finland as shown here in 2010 corroborate the concurrent rates in other Scandinavian countries, such as the nationwide prevalence 188.9/10 5 reported in 2008 in Sweden, crude nationwide prevalence 208/10 5 in 2013 in Norway, 154.5 /10 5 in 2005 in Denmark, and 167.1/10 5 in 2007 in Iceland . Although no exact nationwide prevalence estimation exists in Finland, results here and in a recent report based on a national register information point at a globally high nationwide prevalence of 180‐200/10 5 …”

Multiple Sclerosis Incidence and Prevalence Trends in the Province of Padua, Northeast Italy, 1965–2018

“…The 11.4-fold increase in MS prevalence in the Province of Padua over the last 5 decades is in line with similar reappraisals of MS prevalence in other Italian Regions [2,[9][10][11][12], European countries [13][14][15] and North America [16,17]. A similar increase has also been recorded in regions previously considered at low-risk for MS, like Middle-East [18][19][20] and South and East Asia [21].…”

Multiple Sclerosis in Italy: A 40-Year Follow-Up of the Prevalence in Ferrara

“…In our last investigation in the Republic of San Marino, using the same diagnostic criteria and case-finding procedures, the percentage of patients showing minimal moderate or no disability (EDSS score,1-3.5) was 74.6% [35]. Similarly, data compatible with improved survival have been found in other MS populations, including those from Italy [22,25,29,30,37], Norway [9], and Canada [42].…”

“…However, considering great differences in the methods and diagnostic criteria used in the studies, it is hard to compare recent studies with earlier ones and correctly explain the significance of the apparent temporal trend reported from the same areas [2][3]. It is not clear whether the increase in frequency in epidemiological follow-up surveys indicates a change in incidence and prevalence, or reflects improved case identification and ascertainment [8][9].…”