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Twenty patients with optic neuritis (ON) described in the previous study [23] underwent serial VEP recordings (using multiple electrode arrays) for two years. The VEPs could be correlated with the lesions revealed by MRI, Visual Field tests and other clinical findings. On the basis of their scalp distribution, they were classified as "really delayed" VEPs and "pseudo-delayed" VEPs. Real delays could be recorded at the onset of ON or shortly afterwards, and their appearance indicated the recovery of visual function and a good prognosis. Pseudo-delays indicated an alteration in the visual field and, unless a breakthrough of normal or delayed components appeared in the first three months, following acute ON, indicate a poor prognosis for the recovery of visual function. The pseudo-delayed VEPs were mainly observed in patients with longer lesions revealed by means of LTE-STIR MRI [23]; there was no correlation between VEP latency and the length of plaques. Our findings contradict previous theories on the timing of conduction alterations in ON and multiple sclerosis.

Experimental allergic encephalomyelitis (EAE) in its chronic relapsing (CR-EAE), chronic progressive (CP-EAE) and acute (A-EAE) forms was obtained in 24 juvenile strain 13 guinea pigs. Visual, brainstem acoustic and somatosensory evoked potentials (EPs) were recorded in these animals prior to the sensitizing injection and during the course of the disease. Delays in the EPs appeared 15 days post-sensitization (dps), preceding or simultaneously with clinical alterations: electron microscopy revealed myelin stripping and vacuolation in the animals sacrificed 25 dps. Decreases in EP latency were recorded 32 dps; when electron microscopy revealed myelin layers indicating remyelination, whereas light microscopy showed only inflammatory changes. When confluent plaques were revealed by light microscopy 120 dps, the EP wave shapes were distorted or absent. The discussion reviews the literature on early myelin and conduction changes during central demyelination.

Magnetic resonance images of optic nerves were obtained in 20 patients with acute optic neuritis (ON), and assessed by means of clinical, visual field and visual evoked potential evaluations; the imaging was repeated 1 year later. The results of the conventional Short Tau Inversion Recovery (STIR) sequence obtained using short time echo (STE-STIR: 22 msec) were compared with those of the long time echo sequence (LTE-STIR: 80 msec). The conventional STE-STIR sequence revealed lesions in 57.2% cases of acute ON and in 42.9% of the optic nerves affected by previous ON; the LTE-STIR sequence was diagnostic in 95.2% of acute ON cases and in 85% of patients with previous ON. The calculated length of the optic nerve lesions was significantly longer in the images obtained using the LTE-STIR sequence than in those obtained using conventional STE-STIR sequences.