The Optic Neuritis Treatment Trial (ONTT) is a prospective study of co
rticosteroid treatment of acute optic neuritis (ON), with subsequent l
ongitudinal follow-up to determine development of clinically definite
multiple sclerosis (CDMS). We analyzed the CSF of 83 patients with cli
nically isolated ON who underwent lumbar puncture within 24 hours of e
nrollment into the ONTT to determine the value of CSF changes in ON, e
specially regarding diagnostic utility, immunologic changes, MRI corre
lations, and progression to CDMS. All patients had baseline MRI scans
graded for changes typical of MS. CSF measurements included immunoglob
ulin G (IgG) synthesis, IgG ratio, myelin basic protein, IgG kappa lig
ht chains, and oligoclonal banding. No patients had their diagnosis or
management altered as a result of CSF findings. Except for oligoclona
l bands, few patients showed any abnormalities on CSF tests, and no te
sts correlated with the 2-year development of CDMS. Oligoclonal bandin
g, present at baseline in 11 of 13 patients who developed CDMS, did pr
edict progression to CDMS, but this was not independent of MRI abnorma
lities. Two patients with oligoclonal bands and a normal MRI did progr
ess to CDMS. We conclude that CSF analysis may not be necessary in the
routine evaluation of patients presenting with a typical clinical pro
file of acute ON, and that most CSF tests add little additional inform
ation to MRI results for predicting the 2-year development of CDMS. Ho
wever, the precise role of oligoclonal banding in the analysis of such
patients awaits longer follow-up of this cohort.