Trying to understand disease, especially rare disorders, at a global level is a Herculean task; not only from a resources perspective, but also from the cost and logistics involved. Before, the Global Burden of Disease study presented here, there was the Multiple Sclerosis International Federation that provided up to date figures on the global epidemiology of MS back in 2008. So, almost a decade on where do we stand?
Well, MS prevalence is on the up. According to the GBD study the prevalence of multiple sclerosis in 2016 was 2.22 million, representing a 10.4% increase in the age-standardised prevalence since 1990. The greatest rise in figures were seen in the east Asia region (44.8% up) and Canada (81.9% up). While, the greatest overall prevalence was in North-America (164.6 per 100,000), followed by western Europe (127 per 100,000) and then Australasia (91.1 per 100,000); see figure below.
One country stands out above the rest, and that is Greenland. As noted by Stenager in his comment to the journal, there have been no reports of MS among the Inuit inhabitants that make up the majority in Greenland. By his calculation there were approximately 10-12 people with MS living in Greenland, giving rise to a prevalence of 22 cases per 100,000 population, placing Greenland amongst the lowest prevalence countries, rather than indicated by the GBD study.
Like all studies of this ilk, there will be some limitations. Case accrual/reporting is always going to be an issue, particularly from the low income countries, such as Africa and Asia. Conversely, some of the rise in prevalence within high income countries may just represent better access to healthcare services.
What about specifics in the study? An interesting finding for me was that the years of life lost (YLL) due to premature death and disability was greatest in the sixth decade of life (see figure below). While, the years of life lived with disability (YLD) rises to a peak at age 55, then plateaus before climbing again in the 80s. The latter is not to say that MS increases in those older than 80!
Secondly, the female and male prevalence. The two in fact seem to diverge in adolescence, while among the preteen children, the occurrence of MS is similar to that between boys and girls (see figure below). Puberty comes to mind as a possible explanation.
Multiple sclerosis is the most common inflammatory neurological disease in young adults. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) provides a systematic method of quantifying various effects of a given condition by demographic variables and geography. In this systematic analysis, we quantified the global burden of multiple sclerosis and its relationship with country development level.
We assessed the epidemiology of multiple sclerosis from 1990 to 2016. Epidemiological outcomes for multiple sclerosis were modelled with DisMod-MR version 2.1, a Bayesian meta-regression framework widely used in GBD epidemiological modelling. Assessment of multiple sclerosis as the cause of death was based on 13 110 site-years of vital registration data analysed in the GBD’s cause of death ensemble modelling module, which is designed to choose the optimum combination of mathematical models and predictive covariates based on out-of-sample predictive validity testing. Data on prevalence and deaths are summarised in the indicator, disability-adjusted life-years (DALYs), which was calculated as the sum of years of life lost (YLLs) and years of life lived with a disability. We used the Socio-demographic Index, a composite indicator of income per person, years of education, and fertility, to assess relations with development level.
In 2016, there were 2 221 188 prevalent cases of multiple sclerosis (95% uncertainty interval [UI] 2 033 866–2 436 858) globally, which corresponded to a 10·4% (9·1 to 11·8) increase in the age-standardised prevalence since 1990. The highest age-standardised multiple sclerosis prevalence estimates per 100 000 population were in high-income North America (164·6, 95% UI, 153·2 to 177·1), western Europe (127·0, 115·4 to 139·6), and Australasia (91·1, 81·5 to 101·7), and the lowest were in eastern sub-Saharan Africa (3·3, 2·9–3·8), central sub-Saharan African (2·8, 2·4 to 3·1), and Oceania (2·0, 1·71 to 2·29). There were 18 932 deaths due to multiple sclerosis (95% UI 16 577 to 21 033) and 1 151 478 DALYs (968 605 to 1 345 776) due to multiple sclerosis in 2016. Globally, age-standardised death rates decreased significantly (change −11·5%, 95% UI −35·4 to −4·7), whereas the change in age-standardised DALYs was not significant (−4·2%, −16·4 to 0·8). YLLs due to premature death were greatest in the sixth decade of life (22·05, 95% UI 19·08 to 25·34). Changes in age-standardised DALYs assessed with the Socio-demographic Index between 1990 and 2016 were variable.
Multiple 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.