Optic neuritis in the two northernmost counties of Norway. A study of incidence and the prospect of later development of multiple sclerosis.

A study of the incidence of uncomplicated optic neuritis (ON) in the period 1972-1984 and the subsequent risk of later developing of multiple sclerosis (MS) was performed in the two northernmost counties of Norway. The incidence of ON was stable during the period. Of the 36 ON patients available to follow-up, 42% later developed MS. Mean time from debut of ON to the next symptom of MS was 2.2 years, median 1 year. There was one ethnic Lapp among the ON patients. The number of Lapps in the area is estimated to be about 26,000.