Occurrence of multiple sclerosis in central Finland: a regional and temporal comparison during 30 years

OBJECTIVE: We estimated the prevalence and incidence of multiple sclerosis (MS) in central Finland up to 2000. Rates were compared with those in other areas in Finland. MATERIAL AND METHOD: MS cases were identified in the hospital registry by ICD codes for demyelinating diseases from 1979 to 2000. Cases with definite MS were included. Incidence and prevalence were calculated with 95% CI and standardization was performed using direct method. RESULTS: In 1993 prevalence was 59/10(5) (n = 153). Incidence in 1979-93 was 3.8/10(5) person-years (n = 126). Rates are similar to average in areas with known rates of MS in Finland but substantially less than the over twofold MS risk in the neighbouring district Seinajoki. Extended follow-up to 2000 in central Finland showed increasing prevalence up to 105/10(5) (n = 277) and a significant increase in incidence 1994-98 up to 9.2/10(5) (n = 105). At the same time the diagnostic use of MRI increased up to 97%. CONCLUSION: Central Finland represents an average risk area of MS when compared with other areas of Finland but still a high risk in global comparison. The recent rapid increase in both prevalence and incidence is largely accounted for by increased use of MRI.