A global perspective on the burden of multiple sclerosis

Multiple sclerosis is the most common neuroimmunological disorder. Onset is usually seen in young adults and the disease course is characterised by long survival and increasing disability over time. Owing to medication being expensive, the need for continuous care, and rehabilitation in the late stages of the disease, multiple sclerosis is putting increasing demands on health-care resources. In The Lancet Neurology, the GBD 2016 Multiple Sclerosis Collaborators1GBD 2016 Multiple Sclerosis CollaboratorsGlobal, regional, and national burden of multiple sclerosis 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016.Lancet Neurol. 2019; (published online January 21.)http://dx.doi.org/10.1016/S1474-4422(18)30443-5Google Scholar provide a basis for estimating this demand in their analysis of the global, regional, and national burden of multiple sclerosis from 1990 to 2016. The report is based on data from the Global Burden of Diseases, Injuries, and Risk Factors study,2GBD 2015 Neurological Disorders Collaborator GroupGlobal, regional, and national burden of neurological disorders during 1990–2015: a systematic analysis for the Global Burden of Disease Study 2015.Lancet Neurol. 2017; 16: 877-897Summary Full Text Full Text PDF PubMed Scopus (1199) Google Scholar in which modelling provides estimates of disease prevalence. Deaths are summarised as disability-adjusted life-years, and the Socio-demographic Index (SDI), a composite indicator of income per person, years of education, and fertility, is used to assess outcomes in relation to country development level. The prevalence of multiple sclerosis in 2016 was 2·22 million, representing a 10·4% (95% uncertainty interval 9·1–11·8) increase in the age-standardised prevalence since 1990. Prevalence increased with increasing latitude, being lowest in eastern sub-Saharan Africa (3·3 cases per 100 000 population, 95% uncertainty interval 2·9–3·8), central sub-Saharan African (2·8, 2·4–3·1), and Oceania (2·0, 1·71–2·29), and highest in North America (164·6, 153·2–177·1), western Europe (127·0, 115·4–139·6), and Australasia (91·1, 81·5–101·7). Additionally, there was a strong female preponderance. The authors note that the increasing prevalence of multiple sclerosis could partly be explained by decreases in disease-related mortality. As a limitation, the authors discuss the statistical collinearity between SDI and distance from the equator, which might mean that results are not always robust for a single predictor, such as latitude. However, as the regions with the highest prevalence of multiple sclerosis also have the most detailed data, this finding might reflect that high-income countries provide the most rigorous epidemiological studies. If so, the prevalence data from the remaining regions, which, as the authors point out, are sparse or incomplete, should be interpreted cautiously. Furthermore, socioeconomic factors are not a major risk factor for multiple sclerosis overall,3Nielsen NM Jørgensen KT Bager P et al.Socioeconomic factors in childhood and the risk of multiple sclerosis.Am J Epidemiol. 2013; 177: 1289-1295Crossref PubMed Scopus (29) Google Scholar although can have important effects for individual patients in high-income regions, such as reduction in income and living standards.4Pfleger CC Flachs EM Koch-Henriksen N Social consequences of multiple sclerosis (1): early pension and temporary unemployment—a historical prospective cohort study.Mult Scler. 2010; 16: 121-126Crossref PubMed Scopus (99) Google Scholar By far, the most surprising finding in the GBD 2016 analysis of multiple sclerosis1GBD 2016 Multiple Sclerosis CollaboratorsGlobal, regional, and national burden of multiple sclerosis 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016.Lancet Neurol. 2019; (published online January 21.)http://dx.doi.org/10.1016/S1474-4422(18)30443-5Google Scholar is that Greenland had the highest age-standardised prevalence, with more than 270 cases per 100 000 general population. This estimate, however, was based on one survey of chronic diseases that estimated prevalence of multiple sclerosis on the basis of hospital records in a community of fewer than 2000 inhabitants in the period 1950–74, during which no cases of multiple sclerosis were reported.5Kromann N Green A Epidemiological studies in Upernavik District, Greenland. Incidence of some chronic diseases 1950-1974.Acta Neurol Scand. 1980; 208: 401-406Crossref Scopus (776) Google Scholar Of note, native Inuits made up more than 90% of the Greenland study population in the 1950–74 observation period, and no cases of multiple sclerosis have been reported among Inuits in Greenland.5Kromann N Green A Epidemiological studies in Upernavik District, Greenland. Incidence of some chronic diseases 1950-1974.Acta Neurol Scand. 1980; 208: 401-406Crossref Scopus (776) Google Scholar In 2016, approximately 10–12 people with multiple sclerosis were living in Greenland (unpublished data), which gives a prevalence of less than 22 cases per 100 000 general population. Most of the patients were of Danish ancestry living temporarily in Greenland, probably including some of mixed ethnicity, but none was registered as ethnic Inuit. Greenland, therefore, should have a prevalence value among the lowest on the map in the GBD report. Greenland is geographically close to North America but comprises a realm along with the Faroe Islands and Denmark. Surveillance of health issues and allocation of resources are partly collaborative and all contribute to a joint multiple sclerosis registry. People in Greenland suspected of having multiple sclerosis are diagnosed and treated at the Rigshospitalet in Copenhagen, Denmark. The reason for the Faroe Islands not being included in the GBD 2016 study is unclear, especially given that increasing prevalence of multiple sclerosis on the islands has been reported.7Wallin MT Heltberg A Kurtzke JF Multiple sclerosis in the Faroe Islands. 8. Notifiable diseases.Acta Neurol Scand. 2010; 122: 102-109PubMed Google Scholar The GBD 2016 Multiple Sclerosis Collaborators cite this report, although they exclude another that showed low incidence in the Faroe Islands8Joensen P Multiple sclerosis: variation of incidence of onset over time in the Faroe Islands.Mult Scler. 2011; 17: 241-244Crossref PubMed Scopus (14) Google Scholar that would not give reason to expect high prevalence. Furthermore, data from Scotland, Northern Ireland, and Ireland9Mackenzie IS Morant SV Bloomfield GA MacDonald TM O'Riordan J Incidence and prevalence of multiple sclerosis in the UK 1990-2010: a descriptive study in the General Practice Research Database.J Neurol Neurosurg Psychiatry. 2014; 85: 76-84Crossref PubMed Scopus (198) Google Scholar also suggest that high prevalence would not be expected in the Faroe Islands. The data for Greenland and the Faroe Islands do not support the conclusion of the GBD 2016 Multiple Sclerosis Collaborators that prevalence increases with increasing latitude, at least in that region of the North Atlantic. Given my reservations, I advise extreme caution in using the results from nations or regions with few or no studies or with studies that have no clearly defined and comparable methods. I agree with the GBD 2016 Multiple Sclerosis Collaborators that policy makers, administrators, care providers, and multiple sclerosis societies globally should call for valid information to improve resource allocation and health-service planning, but the first step should be to encourage the formation of administrative registers in nations and regions to enhance the accuracy of estimates. The next step could be to use the data to remap the burden of multiple sclerosis. I declare no competing interests. Global, regional, and national burden of multiple sclerosis 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016Multiple sclerosis is not common but is a potentially severe cause of neurological disability throughout adult life. Prevalence has increased substantially in many regions since 1990. These findings will be useful for resource allocation and planning in health services. Many regions worldwide have few or no epidemiological data on multiple sclerosis, and more studies are needed to make more accurate estimates. Full-Text PDF Open Access