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Epidemiological Studies of Multiple Sclerosis in Sweden with focus on the County of Värmland
Linköping University, Department of Clinical and Experimental Medicine, Neurology. Linköping University, Faculty of Health Sciences.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this thesis was to study the frequency of MS in the suggested high-risk area of Värmland county by investigating the current prevalence and analyzing the development over time; secondly to investigate some aetiological factors – the pattern of industry, both in relation to MS in Värmland and in the whole country, and also to examine the possible relation between the distribution of MS and ALS, as it has previously shown a positive correlation in two studies; finally to analyze the women-to-men ratio of MS in Sweden because of international reports of an increasing ratio.

Clinical data was collected from hospitals and other health care units in the county of Värmland, to calculate the prevalence ratio. The prevalence was 170.07 per 100,000 population on the prevalence day, 31 December 2002. The incidence rates analysed during ten years was 6.46 per 100,000 personyears (1991-1995) and 6.39 (1996-2000).

The ecological study used data from the beginning of the 20th century on industries in Värmland and in all Sweden, which were correlated with the two MS prevalence studies (1925-1934 and 2002), and the mortality study on the time period 1952-1990. There was a statistical significant association between large sawmills and the prevalence 1925-1934 (p = 0.022). For all Sweden, wood-pulp factories and papermills correlated significantly with MS mortality 1952-1990 (p = <0.05).

Collected data from Causes of death Register and from the Total Population Register were used when analysing mortality from ALS and MS. The previously shown correlation between ALS and MS mortality distribution in the Swedish counties was not confirmed in this study. However, the mean MS mortality rate was still highest in the county in Värmland. The mean MS mortality rates for whole Sweden was increased from 1.65 per 100,000 person-years (1952-1992) to 2.04 (1990-2010).

For analysing sex ratio in MS, data from the Swedish Multiple Sclerosis Register and data from Total Population Register of the Swedish Statistics Office were used. These data was analysed by birth day cohort and by year of onset. The sex ratios in Sweden showed a stable women-to-men ratio.

These investigations give indication that Värmland is a high-risk region of multiple sclerosis, and particularly the municipality of Säffle.

We conclude that Värmland is a suitable area for continued epidemiological studies with both an environment and genetic focus.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. , 52 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1286
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-74177ISBN: 978-91-7519-990-0 (print)OAI: oai:DiVA.org:liu-74177DiVA: diva2:480873
Public defence
2012-02-17, Sal Linden, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2012-01-20 Created: 2012-01-20 Last updated: 2012-02-15Bibliographically approved
List of papers
1. High prevalence of multiple sclerosis in the Swedish county of Värmland
Open this publication in new window or tab >>High prevalence of multiple sclerosis in the Swedish county of Värmland
2009 (English)In: Multiple Sclerosis, ISSN 1352-4585, E-ISSN 1477-0970, Vol. 15, no 11, 1253-1262 p.Article in journal (Refereed) Published
Abstract [en]

Previous epidemiological studies have indicated that the county of Värmland in western Sweden may be a high-risk zone for multiple sclerosis (MS). The objective of this study was to determine the prevalence in the area. Hospital and general practice medical files were scrutinized. The diagnostic criteria of Poser were used, with 31 December 2002 as prevalence day. The prevalence was 170.07 per 100,000 inhabitants. The average annual incidence was 6.39 to 6.46 per 100,000 (1991—1995, 1996—2000). Multiple sclerosis was 2.3 times more common among women than men. There was a variation in prevalence among the 16 municipalities, however it was not statistically significant. The rates seemed highest in the southwestern part of the county, roughly similar in location to findings some 70 years earlier. When the prevalence ratios by geographical units for the county in 1933 were applied to the current prevalence, the distribution from these estimated cases differed from homogeneity with very high significance (p < 0.00001 ). In conclusion, this study supports previous reports indicating that Värmland continues to be a high-risk zone for MS and shares in the diffusion of the disease at the county level which we had presented for the country as a whole.

Keyword
epidemiological, risk, aetiological, genetics, environment
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-51888 (URN)10.1177/1352458509345909 (DOI)
Available from: 2009-11-23 Created: 2009-11-23 Last updated: 2017-12-12Bibliographically approved
2. An ecological study of industry in a high-risk region of multiple sclerosis
Open this publication in new window or tab >>An ecological study of industry in a high-risk region of multiple sclerosis
2011 (English)In: Journal of the Neurological Sciences, ISSN 0022-510X, E-ISSN 1878-5883, Vol. 311, no 1-2, 50-57 p.Article in journal (Refereed) Published
Abstract [en]

The county of Varmland, Sweden, has shown a high frequency of multiple sclerosis in several investigations. It has been presented in three studies: a period prevalence study in 1925-1934, a mortality study during 1952-1992 and a prevalence investigation in 2002. The aim of this study was to investigate the pattern of industry in this high-risk area for multiple sclerosis. The three investigations were correlated with industry in 1913 and in the 1950s, all analyzed by the Kruskall-Wallis test. Select industries from wood-pulp, paper and iron/mechanical sectors were tested also in whole Sweden. The Spearman rank correlation was used for these data and forestry data in Varmland. In Varmland, industrial data from 1913 revealed that large sawmills were associated with the period prevalence in 1925-1934 and there was a possible correlation with the prevalence for 2002. Wood-pulp factories showed a possible association with the prevalence 1925-1934 and the mortality 1952-1992. Some industries in the 1950s were correlated with the prevalence 2002. Wood and paper industries in Sweden 1913 showed an association with the MS mortality 1952-1992. In summary, data on MS prevalence in Varmland and mortality both in Varmland and all Sweden from the past 100 years suggest an association with wood-related industries in 1913 and in the 1950s, whereas no consistent association was found for other industries.

Place, publisher, year, edition, pages
Elsevier, 2011
Keyword
Multiple sclerosis; Prevalence; Mortality; Environmental; Ecological; Pollutions; Industry
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-73732 (URN)10.1016/j.jns.2011.09.005 (DOI)000297893400009 ()
Available from: 2012-01-12 Created: 2012-01-12 Last updated: 2017-12-08
3. Mortality Statistics Studies of Multiple Sclerosis and Amyotrophic Lateral Sclerosis in Sweden
Open this publication in new window or tab >>Mortality Statistics Studies of Multiple Sclerosis and Amyotrophic Lateral Sclerosis in Sweden
2012 (English)In: Neuroepidemiology, ISSN 0251-5350, E-ISSN 1423-0208, Vol. 38, no 4, 245-249 p.Article in journal (Refereed) Published
Abstract [en]

Background: Multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS) are chronic neurologic diseases where distinct explanations of the pathogenesis are lacking. Two large Swedish register studies have rather unexpectedly detected a correlation between MS and ALS.

The aim of this study was to investigate if an association between ALS and MS could be demonstrated as has been shown earlier.

Material and methods: Data on mortality from ALS and MS, 1990-2010 were collected from the Swedish national statistics office. In all there were 5,696 deaths due to ALS and 3,941 deaths due to MS. Age- and sex-adjusted mortality rates were calculated.

Results: There was no correlation between the mortality rates of ALS and MS in the 21 counties of Sweden for the period 1990 to 2010 (Spearman’s rho = - 0.052; p = 0.822; n = 21).

The national mean mortality rate for ALS throughout the period of 1990 to 2010 was 2.98 per 100 000 person-years (95% CI 2.87 – 3.08). For MS the national mean mortality rate was 2.04 per 100 000 person-years (95% CI 1.95 – 2.12). Both ALS and MS mortality showed significant variation between the counties. Conclusion: This study did not confirm the previously shown association between MS and ALS in Sweden.

Place, publisher, year, edition, pages
S. Karger, 2012
Keyword
Amyotrophic lateral sclerosis; multiple sclerosis; mortality; correlation, epidemiology, genetics
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-74175 (URN)10.1159/000338031 (DOI)000305659200008 ()
Available from: 2012-01-20 Created: 2012-01-20 Last updated: 2017-12-08Bibliographically approved
4. Sex ratio of multiple sclerosis in Sweden
Open this publication in new window or tab >>Sex ratio of multiple sclerosis in Sweden
2013 (English)In: Multiple Sclerosis, ISSN 1352-4585, E-ISSN 1477-0970, Vol. 13, no 1, 46-52 p.Article in journal (Other academic) Published
Abstract [en]

Sex ratio of multiple sclerosis has been reported from several areas. The disease is more common in women. In Europe the women-to-men ratio varies from 1.1 to 3.4. Recently a study in Canada has reported a significant increased female-to-male ratio in multiple sclerosis.

Our objective was to analyse the development of sex ratio in multiple sclerosis in the Swedish population.

Data from the Swedish MS Register and data from the Swedish National Statistics Office were used to estimate sex ratio by year of birth and year of onset.

In analyse of sex ratio by year of birth there were 8,834 patients (6,271 women and 2,563 men) born during 1931 to 1985. The mean value of women-to-men ratio was 2.62. No clear trend was noted for the women-to-men ratio by year of birth (Spearman’s rho = 0.345, p=0.298, n=11). Patients analysed by year of onset was 9,098 (6,452 women and 2,646 men) during the study time period 1946 until 2005. The mean women-to-men ratio was 2.57. There was no significant change of the women-to-men ratio (Spearman’s rho = -0.007, p = 0.983, n = 12).

Conclusion: In the Swedish patients there was no evidence for an increased womento-men ratio in multiple sclerosis.

Keyword
Multiple sclerosis, sex ratio, incidence rate, prevalence proportion, SMSreg
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-74176 (URN)10.1177/1352458512446169 (DOI)000313272100009 ()
Available from: 2012-01-20 Created: 2012-01-20 Last updated: 2017-12-08Bibliographically approved

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