Multiple sclerosis in the far north--incidence and prevalence in Nordland County, Norway, 1970-2010.

Espen Benjaminsen,Johnny Olavsen,Merethe Karlberg,Karl B Alstadhaug

doi:10.1186/s12883-014-0226-8

Espen Benjaminsen, Johnny Olavsen + Show 2 more

Open Access

https://doi.org/10.1186/s12883-014-0226-8

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Abstract

BackgroundThe risk of multiple sclerosis (MS) increases with increasing latitude. Taking into consideration that Norway has a large latitude range, a south-to-north gradient would be expected. However, previous studies have reported an uneven distribution of the disease in Norway, with a relatively low prevalence in the most northern parts of the country.We describe the incidence and prevalence of MS in a county in the north of Norway over a period of 40 years.MethodsAll patients with MS living in Nordland County in the period 1970–2010 were identified by reviewing hospital charts. The patients were included if they met the criteria of definitive or probable MS according to Poser [Ann Neurol 13:227-231, 1983] or MS according to McDonalds [Ann Neurol 50:121-127, 2001]. Point prevalence at the beginning of the decades was calculated. The average annual incidence was calculated for 5-year periods.ResultsThe total crude prevalence on January 1, 2010 was 182.4 per 100 000. The annual incidence continuously increased from 0.7 per 100 000 in 1970 – 1974 to 10.1 per 100,000 in 2005 – 2009. The time delay from the first symptom to diagnosis was stable from 1975 to 2010. The proportion of primary progressive MS in the prevalence numbers was 38.2% in 1980, and decreases continuously, to 18.6% in 2010. The female to male prevalence ratio has been stable since 1990 at 2.2 to 1.ConclusionThe prevalence and the incidence of MS have steadily increased over a 40 year period. Nordland County is a high-risk area for MS.

Highlights

The risk of multiple sclerosis (MS) increases with increasing latitude
MS is associated with the human leukocyte antigen DRB1*15DQB1*06, and the Sami have a low frequency of this haplotype [19]
The point prevalence rate was defined as the proportion of the population in Nordland County with definitive or probable MS according to Poser or MS according to McDonalds at a specified time point

Summary

Introduction

The risk of multiple sclerosis (MS) increases with increasing latitude. Taking into consideration that Norway has a large latitude range, a south-to-north gradient would be expected. Previous studies have reported an uneven distribution of the disease in Norway, with a relatively low prevalence in the most northern parts of the country. We describe the incidence and prevalence of MS in a county in the north of Norway over a period of 40 years. Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease in the central nervous system with unknown aetiology. A latitude dependent gradient in the occurrence has been shown in many countries and regions. Norway has a long and narrow landscape, with the mainland stretching from 57° N to 71° N, Sami people of northern Scandinavia seem to be partly protected against MS. MS is associated with the human leukocyte antigen DRB1*15DQB1*06, and the Sami have a low frequency of this haplotype [19]

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