DELAYED AND PSEUDODELAYED VISUAL-EVOKED POTENTIALS IN OPTIC NEURITIS COMPARED WITH LONG-TIME ECHO-SHORT TAU INVERSION-RECOVERY MAGNETIC-RESONANCE-IMAGING OF OPTIC-NERVE

Twenty patients affected by optic neuritis (ON) underwent serial visua l evoked potential (VEP) recordings, performed with multiple electrode arrays, and with stimuli of 1 and 3 cycles per degree (cpd) for 1 yea r. VEP findings were correlated with long time echo-short tan inversio n recovery (LTE-STIR) magnetic resonance imaging (MRI) of optic nerves and with visual field tests. MRI showed lesions in 95.2% of acute ON and in 66.6%of the,l year follow-up. VEPs were classified into really 'delayed' VEPs and 'pseudodelayed' VEPs, based on their scalp distribu tion. Furthermore, VEPs to 1 or 3 cpd could be 'delayed' or 'pseudodel ayed' in the same patient. Real delays could be recorded at onset or s hortly after ON, and indicated the possibility of recovery of visual f unctions and good functional prognosis. Pseudodelays, to 3 cpd, corres ponded to prominent central scotomata and indicated poor prognosis for the recovery of visual function, unless a breakthrough of normal or d elayed components appeared in the first 4 months following acute ON. P seudodelayed VEPs clustered in patients with longer demyelinating lesi ons, as shown by LTE-STIR MRI. There was no correlation between latenc y of VEPs and length of plaques. Our study addresses some reconsiderat ions of the pathophysioiogy of conduction delay in acute optic neuriti s.