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 visual evoked potential (VEP) recordings, performed with multiple electrode arrays, and with stimuli of 1 and 3 cycles per degree (cpd) for 1 year. VEP findings were correlated with long time echo-short tau inversion 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 1 year follow-up. VEPs were classified into really 'delayed' VEPs and 'pseudodelayed' VEPs, based on their scalp distribution. Furthermore, VEPs to 1 or 3 cpd could be 'delayed' or 'pseudodelayed' in the same patient. Real delays could be recorded at onset or shortly after ON, and indicated the possibility of recovery of visual functions and good functional prognosis. Pseudodelays, to 3 cpd, corresponded to prominent central scotomata and indicated poor prognosis for the recovery of visual function, unless a breakthrough of normal or delayed components appeared in the first 4 months following acute ON. Pseudodelayed VEPs clustered in patients with longer demyelinating lesions, as shown by LTE-STIR MRI. There was no correlation between latency of VEPs and length of plaques. Our study addresses some reconsiderations of the pathophysiology of conduction delay in acute optic neuritis.