Epidemiology of Multiple Sclerosis in Western Finland in 1981-2010

The epidemiology of multiple sclerosis (MS), an autoimmune inflammatory disease of the central nervous system, is characterized by uneven global and regional distribution. The highest prevalence and incidence figures are reported from North America and Europe, where especially Scandinavia is considered an area of high MS risk. One area of globally high risk in Finland is the Seinäjoki region, South Ostrobothnia, in western parts of the country, which was already seen in the first epidemiological studies in the 1960s. Another area of high risk is located in Southwest Finland. Globally, the incidence and prevalence of MS have been rising, and studies from Western Finland show similar trends. Survival in MS is reported to be shortened by several years, and shorter if other illnesses, comorbidities, occur. MS is a progressive disease, eventually leading to disability accumulation and difficulties in everyday life, both of which are also increased by comorbidities. Risk of comorbid diseases is reported to be increased among the MS population, and especially vascular diseases worsen survival in MS. The risk of infections is high, and they are the main cause of death in this population.

The main aim of this thesis is to examine the trajectory of MS from an epidemiological point of view, divided in three more specific aims covered in four original studies. The first aim was to update incidence and prevalence trends and study disability distribution in high- and medium-risk areas in Western Finland (studies I and II). The second aim was to assess common comorbidities and their effects on survival for the first time in the Finnish MS population (study III). The third aim was to describe the end-of-life circumstances in the MS population, including disability distribution, causes, and places of death (study IV). The data were derived from hospital patient registers in Seinäjoki, Vaasa, Tampere, and Turku, and archives of Statistics Finland.

In study I, the incidence of MS increased significantly from 1981 to 2010, most remarkably among women and the relapsing-remitting course of the disease (RRMS). In Seinäjoki and Vaasa, the increasing trend stabilized in the last 10-year period of the study, 2000-2010. The age-adjusted incidence/105 was highest in Seinäjoki, 12.5, being twofold compared to 6.7 in Pirkanmaa, and significantly higher than 8.3 in Vaasa. Following similar trends, the results of study II from 2000 to 2010 show that the prevalence of MS increased by 58% among women and 31% among men. Here as well, the increase was more remarkable in the RRMS group, 60%. The most remarkable increase was seen among women in Seinäjoki and Vaasa, where the standardized prevalence/105 in 2010 was 276 in Seinäjoki and 226 in Vaasa. In Pirkanmaa, the rate was 149. Disability in 2010 was mild in the majority of RRMS cases, whereas in the PPMS group, disability was more often severe (EDSS 6.0 or more). The analysis in study III assessing comorbidities and survival from 2004 to 2012 found significantly higher ORs in the MS population for cerebral stroke and hemorrhages, diabetes mellitus type 1, and infections. The mean lifetime survival in MS was 82.4 years, three years shorter than in the matched control population. With cardiovascular comorbidity, the survival time in MS was even worse, 79.5 years. Assessing the end-of-life circumstances of MS patients from 1981 to 2010 in study IV, the mean age at death was 57.4 years. In the majority of cases, disability before death was severe (EDSS 6.0 or more). The immediate cause of death (ICD) was an infection in 51% of cases, whereas MS was the main underlying cause of death (UCD) in 58% of cases. Cardiovascular causes were seen as ICD mainly in the ages 60 years and older and suicide in the youngest group, under 50 years old. Most often MS patients perished in hospital wards.

Our results corroborate earlier findings from the high-risk area in Western Finland and show increasing trends in the incidence and prevalence of RRMS, especially among women. In the future updating the epidemiological figures from this historically unique area of high MS risk remains important. Epidemiological studies provide important background information when plans for future health care are being made, as well as important data for future studies of the efficacy of disease modifying treatments, which are important reasons to continue research in this area. In future studies, we hopefully see the effects of new disease modifying medications on disability and survival. Cardiovascular comorbidities significantly affect survival in MS, which is why it is important to pay attention to the primary prevention of these diseases in the MS population. The inspection of disability results show that greater disability is more often seen in PPMS and is quite common at the end of life. Regarding the accumulation of disability toward the end of life, cut points to create plans for the care at the end of life should be adopted, to ensure proper utilization of palliative care in this patient group as well.