Multiple sclerosis in Nord-Trondelag County, Norway: a prevalence and incidence study

OBJECTIVE: To calculate the prevalence and incidence of multiple sclerosis (MS) in Nord-Trøndelag County, Norway. MATERIAL AND METHODS: The study comprised everyone diagnosed with MS according to the Poser criteria. On 1 January 2000 a total of 208 were identified: 130 women (62.5%) and 78 men (37.5%). We calculated the crude and age-adjusted annual incidence rates from 1974 to 1999. RESULTS: The prevalence on 1 January 2000 was 163.6 of 100,000, 204.8 of 100,000 for women and 122.6 of 100,000 for men. The age-adjusted annual incidence increased from 3.9 to 5.6 per 100,000 from 1974 to 1999; women from 4.6 to 6.3 and men from 2.2 to 4.4. After 1984, the incidence among women increased most, peaking at 10.2 per 100,000 in 1984-88. CONCLUSIONS: MS incidence is increasing in Nord-Trøndelag County. The prevalence is among the highest ever in Norway.