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The frequency with which multiple sclerosis develops after an attack of acute optic neuritis varies widely in different series and has been reported to range from 11.5% to 85%.1 The variability in the findings may relate to different methods of patient selection, diagnostic criteria, geographical factors, duration of follow up, and study design.
A cohort of 82 patients (59 females, 23 males) with uncomplicated ON aged 10 to 50 years (mean 29.2) who were examined neurologically and had visual evoked responses (VERs) performed in our department during the period 1973–83 were re-examined in 1983–85. Twenty six of the patients (32%) had progressed to probable or clinically definite multiple sclerosis during the follow up period of 7–114 (mean 57) months. Female sex, young adult age, and the presence of HLA-B7 or DR2 seemed to increase the risk of developing the disease.2
Seventy one of the 82 (87%) (52 females, 19 males) were reviewed in 1991–2; 11 patients could not be traced. Neurological examination was performed on 49; two patients had died with multiple sclerosis and a telephone questionnaire was completed on the remainder. Thirty three (46%, or 40% of the original 82) had developed probable or clinically definite multiple sclerosis after a mean duration of 13.25 years (range 8–29.6 years). Eight cases had developed multiple sclerosis since the previous review. Kaplan-Meier and actuarial methods of assessment,3 predicted that 52% would develop the disease after 15 years (figure). There was a significantly greater risk of developing multiple sclerosis for patients in the 21–30 year age group than those outside this range but there was no significant difference in the rate of progression to the disease for males and females. There was no significant difference in the probability of developing multiple sclerosis in patients with single or recurrent attacks of optic neuritis or bilateral optic neuritis, nor in those who were DR-2 positive (table 1).
The finding in the Australian cohort that 52% of patients with optic neuritis were at risk of developing probable or clinically definite multiple sclerosis in 15 years is comparable with that of 57% in 11.6 years in the United Kingdom,4 49% in 20 years in the United States,1 and 45% in 15 years in Sweden.5