Abstract
The traditional view, based on numerous early studies and reviews, is that MS is particularly
prevalent in temperate zones both on the northern and southern hemisphere. This uneven
distribution of MS can be attributed to differences in genes and environment and their
interaction. Diagnostic accuracy and case ascertainment are sources of error and have
their shares in the geographical and temporal variations, and improvements in diagnostic
accuracy and case ascertainment influence incidence- and prevalence rates. In addition
the prevalence also depends on survival. With this meta-analysis we have focused on
the trend in the incidence and sex ratio of MS through the last five decades, and
we have analyzed the latitudinal distribution of MS incidence, based on a recent literature
search. Our findings indicated that the prevalence and incidence rates had increased
in almost all areas, but the previously reported latitudinal gradient of incidence
of MS in Europe and North America could not be confirmed even when restricting the
search to surveys published before 1980 or 1970. Conversely, the latitudinal gradient
of prevalence rates seemed to be preserved. This apparent discrepancy can be explained
by the circumstance that incidence estimates only depend on complete ascertainment
for a relative short recent period of time, whereas reliable prevalence rates presuppose
complete ascertainment decades back in time. A contributory explanation for the missing
latitudinal gradient for incidence may be changes in environmental factors, levelling
out differences in habits of life across Europe and North America, and, not least,
that the interpretation of a latitudinal gradient in Europe was based primarily on
prevalence studies and reviews.
In addition, we observed in most regions a profound increase in female incidence of
MS. The last observation should prompt epidemiological studies focusing on change
in female life style.
Keywords
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Article info
Publication history
Published online: October 10, 2011
Accepted:
September 5,
2011
Received in revised form:
September 2,
2011
Received:
June 2,
2011
Identification
Copyright
© 2011 Elsevier B.V. Published by Elsevier Inc. All rights reserved.
