New data identify an increasing sex ratio of multiple sclerosis in Sweden.
BACKGROUND
An increasing women-to-men ratio in later birth cohorts of patients with multiple sclerosis (MS) has been observed in several populations and has been hypothesised to be due to one or several environmental factors of importance for disease aetiology. However, in a study based on data from the Swedish MS registry (SMSreg) this ratio was recently reported to be rather stable during the 20(th) century.


OBJECTIVE
The purpose of this study was to reinvestigate the women-to-men ratio in Sweden based on data from all available data sources, including deceased patients.


METHODS
We combined data from the SMSreg with data from national patient registers.


RESULTS
In total we obtained information on 19,510 MS patients born 1931-1985, 13,321 women and 6189 men. The women-to-men ratio increased from 1.70 for patients born in the 1930s to 2.67 for patients born in the 1980s. When comparing the coverage of SMSreg to the full data set, a significantly higher proportion of women born 1931-1935 compared to men born in the same period were found in SMSreg, resulting in a sampling bias hiding the increasing sex ratio in the full material.


CONCLUSIONS
The women-to-men ratio in MS has increased in Sweden during the 20(th) century similarly to observations in other western countries.
Karolinska Institutet, The Multiple Sclerosis Research Group, Tomebodavägen 18A:05, Stockholm, Solna, 17177, Sweden Helga.Westerlind@ki.se.
Helga
H
Westerlind
Linköping University, Sweden.
Inger
I
Boström
Karolinska Institutet, Sweden.
Leszek
L
Stawiarz
Linköping University, Sweden/Neurology Unit, General Hospital, Motala, Sweden.
Anne-Marie
AM
Landtblom
Karolinska Institutet, Sweden/Lung and Allergy Unit Astrid Lindgren Children's Hospital, Karolinska University Hospital, Solna Sweden.
Catarina
C
Almqvist
Karolinska Institutet, Sweden.
Jan
J
Hillert
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000175:diagnosis / Q000453:epidemiology*; D015995:Prevalence; D012042:Registries; D012744:Sex Ratio; D013548:Sweden / Q000453:epidemiology
Multiple sclerosis; epidemiology; prevalence proportion; register study; sex ratio