A to Z of MS Prevalence and incidence of multiple sclerosis

The study of the geographical distribution of a condition and patterns of disease as it affects groups of people is called epidemiology.

Terminology

Prevalence

the number of people with a condition. Usually measured in cases per 100,000

Incidence

the number of new cases of a condition within a set period of time, usually a year

An estimated 2,500,000 people in the world have multiple sclerosis. Research suggests the proportion of women with MS is increasing and that roughly three women have MS for every man with the condition.

The distribution of MS around the world is uneven. Generally, the prevalence increases as you travel further north or south from the equator. Those parts of Asia, Africa and America that lie on the equator have extremely low levels of MS, whilst Canada and Scotland have particularly high rates.

Race

A simple geographical spread is not the whole picture. Studies show that certain ethnic groups have a markedly lower prevalence of multiple sclerosis, despite living in countries where MS is common. For instance, the Sami or Lapps of northern Scandinavia and the Inuits in Canada have very low rates of MS. A similar pattern is observed amongst the Maoris of New Zealand.

The fact that MS is most prevalent in northern Europe, North America, Australia and New Zealand has led to speculation that it has been carried around the world by European colonists and settlers. It has been suggested that the origins can be traced back to the Vikings who colonised those parts of Northern Europe where MS is most pronounced and that 'Viking genes' can make people particularly susceptible to MS.

It has also been noted that Scotland has a much higher rate of MS than England or Wales and that areas of high MS prevalence around the world have been settled by Scottish immigrants. In Ireland for instance, the national prevalence rate of MS in the Irish Republic - based on an old study from 1971 - is about 66. In Northern Ireland, which was extensively settled by immigrants from Scotland from the 17th century, the rate was recorded in 1996 as 168.

Multiple sclerosis in the UK

Studies in the UK have suggested that the prevalence rate in England and Wales is perhaps between 100 and 140 per 100,000, about 170 in Northern Ireland and as high as 190 in Scotland. Individual studies in Orkney have recorded rates of over 200.

There is as yet no national register of people with MS in the UK. In 2009, research by the London School of Hygiene and Tropical Medicine based on records held by GPs suggested that the figure may be around 100,000. This research has not yet been published in a peer reviewed journal.

Similarly, there is no accurate record of the number of new cases of MS being diagnosed each year. If the results of local area studies are applied nationwide it suggests that about 2,500 people in the UK are diagnosed with MS each year, or about 50 a week.

Bibliography

Compston A, et al.
McAlpine's multiple sclerosis (4th ed).
London:Churchill Livingstone;2005.

Rosati G.
The prevalence of multiple sclerosis in the world: an update.
Neurological Sciences 2001;22:117-139.
abstract

Orton SM, et al.
Sex ratio of multiple sclerosis in Canada: a longitudinal study.
Lancet Neurology 2006;5(11):932-936.
abstract

Prevalence of MS in the UK revised
MS Trust news item - 12 June 2009
read news item

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