Objective: Recent reports provide consistent evidence that Spain is an area of high risk for multiple sclerosis (MS) according to prevalence surveys. However, the studies of incidence are scarce. The objective of the current work is to analyse whether the increased prevalence of MS is accompanied by increasing incidence in the area of Bajo Aragón, northeastern Spain.
Methods: The data of both prevalence and incidence were retrieved from a prospective register created in 1994 and which included patients with probable or definite MS. Crude and age-standardised rates were calculated from 1994 to 2002 and compared with those found retrospectively in the previous period of 1984-1993.
Results: In January 2003, we found a prevalence rate of 75/100,000 (95% CI: 52-97) whereas it was 35/100,000 (95% CI: 20-50) in 1994. In a period of 9 years, 25 new cases were diagnosed in the area with a mean annual incidence rate of 4.6/100,000 (95% CI: 2.8-6.5; range: 1.6-13.6) in comparison to 17 new cases from 1984 to 1993 with a mean incidence rate of 3/100,000 (95% CI: 1.6-4.5). The standardised ratio of incidences was 1.44 (95% CI: 0.95-2.17) and, therefore, the difference of rates was not significant.
Conclusion: We conclude that the increase in prevalence of MS is more likely to be due to improvement on case ascertainment than to increasing incidence. Nonetheless, further prospective incidence studies in larger populations are warranted in Spain to elucidate whether the frequency of this disease is truly increasing.