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Epidemiology of Multiple Sclerosis in Iceland 2002-2007

Epidemiology of Multiple Sclerosis in Iceland 2002-2007


Title: Epidemiology of Multiple Sclerosis in Iceland 2002-2007
Author: Elíasdóttir, Ólöf
Advisor: Elías Ólafsson
Date: 2020
Language: English
University/Institute: Háskóli Íslands
University of Iceland
School: Heilbrigðisvísindasvið (HÍ)
School of Health Sciences (UI)
Department: Læknadeild (HÍ)
Faculty of Medicine (UI)
ISBN: 978-9935-9516-5-6
Subject: MS sjúkdómur; Faraldsfræði; Nýgengi sjúkdóma; Algengi sjúkdóma; Dánartíðni; Læknisfræði; Doktorsritgerðir
URI: https://hdl.handle.net/20.500.11815/1864

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Abstract:

 
Purpose and aims: Multiple sclerosis (MS) is an autoimmune disease that leads to damage in the central nervous system. Although the cause of MS is still unknown, the generally accepted view is that environmental and life-style factors influence the risk of MS in genetically predisposed individuals. The frequency of MS varies between countries. Countries with a more distant position from the equator have the highest reported incidence and prevalence rates. This association may be partially explained by lower exposure to sunlight and low vitamin D levels, two of the established risk factors for MS. According to previous studies the incidence and prevalence of MS appear to have increased since the middle of the past century. Knowledge of changes in disease epidemiology is important to dimension the need for health care resources, especially in light of new and expensive treatment alternatives, but also to identify risk factors of disease. We aimed to assess the incidence (Study I), prevalence (Study II), and mortality (Study IV) of MS in Iceland. In addition, we wanted to assess the influence of birth month in Sweden and Iceland on the risk of being diagnosed with MS later in life (Study III). Such an association has been noted in previous studies and has been hypothesized to be linked with low vitamin D levels during the winter season in pregnant women. Subjects and methods: Studies I, II and IV are population-based, nationwide studies on the epidemiology of MS in Iceland. Cases were identified by searching in multiple sources: administrative databases of both hospitals, private offices and difference government authorities such as the Directorate of Health, and the Social Insurance Administration. When applicable the search was based on diagnosis codes from: ICD10 (G35, G37.9), ICD9 (340, 341) and ICD8 (340, 341). Inclusion criteria for studies I and II were diagnosis of clinically definite MS or primary progressive MS according to the Poser diagnostic criteria. In addition, Study II included patients with laboratory-supported definite MS (LSD-MS) or clinically probable MS (CP-MS) according to Poser’s criteria or those fulfilling the McDonald 2010 criteria. Study IV was based on these prevalence and incidence cohorts. Incidence was calculated for the years 2002–2007 (Study I) and prevalence for the 31st of December 2007 (Study II). Mortality was analyzed by calculating the standardized mortality ratio (SMR) with a life table approach (Study IV). For study III data was extracted from the Swedish MS Registry on all MS patients born between 1940 and 1996. An Icelandic group was created for Study III using the same case ascertainment as described for studies II and IV including cases born between 1981 and 1996. Control groups were created based on data from the Swedish Total Population Registry and Statistics Iceland. The analysis was adjusted for birth year and birth place. Results: We identified 136 patients diagnosed with MS in Iceland in 2002–2007. The mean annual incidence was 7.6 per 100 000 population. The female-to-male sex ratio was 3:1. Mean age at diagnosis was 36.3 years (Study I). There were 526 patients alive on the prevalence day, December 31st 2007. The prevalence was 176 per 100 000 population (Study II). We found no connection between birth month and risk of developing MS later in life (Study III). The mortality in the prevalence group was higher than in the general population (SMR: 2.0; CI: 1.3 –3.0). For patients diagnosed between 2002 and 2007 there was no difference in mortality compared to the general population after the first 11 years following diagnosis (SMR: 0.95; CI: 0.1-3.0). Cause of death was related to MS in 48% (29/61) of cases (Study IV). Conclusion: In line with recent similar surveys from other countries, we found an increase of incidence and prevalence of MS in Iceland. The current incidence and prevalence of MS in Iceland was of comparable magnitude as in studies from the other Nordic countries. The excess mortality in MS relative to the general population of Iceland is in accordance with results of previous work from other countries. Birth month does not seem to be a risk factor for developing MS later in life. This is in contrast to some previous studies where confounding factors might have influenced the results, although further research is needed for clarification.
 
Tilgangur og markmið: Heila- og mænusigg (multiple sclerosis skammstafað MS) er sjálfsofnæmissjúkdómur sem leggst á miðtaugakerfið. Áhættuþættir MS eru meðal annars D vítamin skortur og fyrri sýking af EBV veiru. Að vera fæddur að vori til hefur verið tengt hærri tíðni á MS miðað við þá sem fæddir eru að hausti/vetri. Tíðni MS sjúkdómsins er mismunandi eftir löndum og er nýgengi og algengi hans hærra á norðurhveli jarðar. Tíðni sjúkdómsins hefur einnig breyst með tímanum og hafa mörg lönd birt faraldsfræðilegar rannsóknir sem sýna aukningu á nýgengi og algengi sjúkdómsins á sl. 50 árum. Mikilvægt er því að hafa nýlegar upplýsingar um tíðni sjúkdómsins sérstaklega í ljósi nýrra og öflugra meðferða sem nú standa til boða. Markmið með rannsóknum okkar var að uppfæra þekkingu um nýgengi og algengi MS sjúkdómsins á Íslandi ásamt því að kanna dánartíðni af völdum sjúkdómsins sem ekki hefur áður verið gert á Íslandi. Einnig könnuðum við áhrif fæðingarmánaðar á áhættu á því að þróa með sér sjúkdóminn síðar á lífsleiðinni. Þátttakendur og aðferðir: Allir sjúklingar sem greindust með MS skv. Poser greiningarskilmerkjum um clinically definite MS og primary progressive MS á árunum 2002–2007 á Íslandi (grein I og II) auk þess voru sjúklingar sem uppfylltu skilmerki Poser um laboratory supported definite MS (LSD-MS), clinically probable MS (CP-MS) og McDonald 2010 greiningarskilmerkin með í grein II um algengi MS. Sjúklingarnir voru fundnir út frá greininganúmerum í ICD10 (G35, G37,9), ICD9 (340,341) og ICD8 (340,341) frá Landspítala, öllum sjálfstætt starfandi taugalæknum, minni spítölum og endurhæfingar– stofnunum, röntgen deild LSH, Domus Medica og Deild lyfjamála á Landspítala (grein I, II og IV). Auk þess frá upplýsingum um örorkubætur vegna MS og hjálpartækja hjá Tryggingastofnun ríkisins og Sjúkratryggingum Íslands (grein II og IV). Nýgengi var reiknað fyrir árin 2002–2007 og algengi fyrir 31.desember 2007. Dánartíðni MS sjúklinga var borin saman við heildarþýði Íslands leiðrétt fyrir aldri og kyni með s.k. life table aðferð. Í grein III voru upplýsingar um MS sjúklinga fengnar frá sænsku MS sjúklingaskránni. Sænski hópurinn var fæddur á árunum 1940–1996 og íslenski hópurinn á árunum 1981–1996. Viðmiðunarhópar voru fengnir frá sænska manntalinu (Swedish Total Population Registry) og Hagstofu. Leiðrétt var fyrir fæðingarári og fæðingarstað. Niðurstöður: Nýgengi MS á Íslandi 2002–2007 var 7,6 á hverja 100 000 íbúa. Sjúkdómurinn var 3 sinnum algengari hjá konum en körlum. Meðalaldur við greiningu var 36,3 ár (Grein I). Algengi MS fyrir 31.desember 2007 var 176 á hverja 100 000 íbúa (Grein II). Áhætta á MS síðar á lífsleiðinni reyndist ekki aukin eftir fæðingarmánuði (Grein III). Dánartíðni MS sjúklinga á Íslandi er tvöfalt hærri en hjá íslensku meðalþýði leiðrétt fyrir kyni og aldri (Standardized mortality ratio SMR: 2,0, 95%CI:1,3–3,0). Enginn munur var á dánartíðni fyrstu 10 árin eftir greiningu (SMR: 0,95, 95%CI:0,1–3,0). Enginn munur var á SMR karla og kvenna með MS. Dánarorsakir MS sjúklinga voru í 48% tilvika (29/61) tengdar MS sjúkdómnum (Grein IV). Umræða: Nýgengi og algengi MS sjúkdómsins á Íslandi er hátt, líkt og birtar niðurstöður frá hinum Norðurlöndunum sýna. Dánartíðni MS sjúklinga er hærri en hjá íslensku meðalþýði og er það í samræmi við erlendar rannsóknir. Fæðingarmánuður er ekki áhættuþáttur fyrir MS síðar á lífsleiðinni. Truflandi þáttur (confounding factor) gæti hafa haft áhrif á niðurstöður fyrri rannsókna, en frekari rannsókna er þörf á því.
 

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