The incidence of optic neuritis and its prognosis for multiple sclerosis

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Abstract
An incidence study of idiopathic optic neuritis (ON) was carried out in 2 geographic areas of Finland for the 9-yr period 1970-1978. The southern province of Uusimaa composes a medium-risk and the western province of Vaasa a high-risk area for multiple sclerosis (MS). The risk for subsequent MS was determined. A total of 315 attacks of ON were recorded in 296 patients. The mean annual age-adjusted incidence for ON in Uusimaa was 2.2 and in Vaasa 2.5 per 100,000 population. The incidence figures remained unchanged all the time. The mean age at onset was 30 yr. Of ON patients, 19% developed MS during the mean follow-up period of 5.1 yr. When the life-table method of analysis was used, the probability of developing MS was 38% in Uusimaa and 24% in Vaasa 9 yr after acute optic neuritis. In Uusimaa the risk of women for MS was significantly higher than in men. In 47%, the MS symptoms and signs developed within 1 yr and in 90% within 5 yr after the initial bout of ON. It is possible that only 1 part of idiopathic ON cases do have a relationship with MS.