ARE VEP ABNORMALITIES IN OPTIC NEURITIS (ON) DEPENDENT ON PLAQUE SIZE- A REAPPRAISAL OF THE PHYSIOPATHOLOGY OF ON BASED ON IMPROVED MRI AND MULTIPLE-LEAD RECORDINGS

Twenty patients with optic neuritis (ON) described in the previous stu dy [23] underwent serial VEP recordings (using multiple electrode arra ys) for two years. The VEPs could be correlated with the lesions revea led by MRI, Visual Field tests and other clinical findings. On the bas is of their scalp distribution, they were classified as ''really delay ed'' VEPs and ''pseudo-delayed'' VEPs. Real delays could be recorded a t the onset of ON or shortly afterwards, and their appearance indicate d the recovery of visual function and a good prognosis.Pseudo-delays i ndicated an alteration in the visual field and, unless a breakthrough of normal or delayed components appeared in the first three months, fo llowing acute ON, indicate a poor prognosis for the recovery of visual function. The pseudo-delayed VEPs were mainly observed in patients wi th longer lesions revealed by means of LTE-STIR MRI [23]; there was no correlation between VEP latency and the length of plaques. Our findin gs contradict previous theories on the timing of conduction alteration s in ON and multiple sclerosis.