Contribution of incidence to increasing prevalence of multiple sclerosis in Alberta, Canada.

Alberta Health Care Insurance Plan (AHCIP) data were used to calculate prevalence and incidence rates for multiple sclerosis (MS) in the general population of Alberta from 1990 to 2004. Multiple sclerosis prevalence rose steadily each year over this time period, from 217.6/100,000 individuals in 1990 to 357.6/100,000 in 2004. Multiple sclerosis incidence fluctuated with a slight increase from 1990 to 2004, at 20.9/100,000 and 23.9/100,000, respectively. Age-specific prevalence rates were higher between ages 30 and 60 in 2004 than in 1990. The pattern of age-specific incidence rates was similar in 1990 and 2004, with a slight shift toward diagnosis in younger years. Gender-specific prevalence rates were higher for females in both 1990 and 2004, with a greater increase in females (43%) than males (29%). Gender-specific incidence rates were higher for females than males in both years, but there was no differential increase in incidence by gender from 1990 to 2004. The 2004 Alberta MS prevalence rate remains among the highest reported worldwide. Both increasing incidence and longer duration have likely contributed to increasing MS prevalence in the province.