Long-term remyelination after optic neuritis - A 2-year visual evoked potential and psychophysical serial study

Thirty-one patients were followed-up, at 3-month intervals for the first ye ar and at 6-month intervals for the second year, after an episode of optic neuritis, The object was to confirm previous evidence for a progressive sho rtening of visual evoked potential (VEP) latencies and to determine whether this is associated with any change in the clinical ocular examination, vis ual fields or contrast sensitivity, VEP latencies were found to decrease si gnificantly during both the first and (less strikingly) the second year, th e most marked changes occurring between 3 and 6 months, Contrast sensitivit y improved during the first 9 months, but subsequently tended (non-signific antly) to deteriorate, A similarly transient improvement in central visual field sensitivity was seen in a subgroup of patients with clinically overt multiple sclerosis, In the data from the acutely unaffected fellow eyes, no significant changes in VEP parameters or functional indices were observed, The findings extend those of a previous study which showed significant sho rtening of VEP latencies between 6 months and 3 years without significant f unctional improvement, Over this period, a significant prolongation of VEP latencies occurred in the asymptomatic fellow eye, accompanied by contrast sensitivity deterioration, Taken in conjunction, the two studies suggest th at recovery processes involving remyelination or, possibly, ion channel reo rganization proceed for at least 2 years, The concurrent effects of insidio us demyelination and/or axonal degeneration (also occurring in the fellow o ptic nerve) are initially masked by the recovery process, but gradually bec ome more evident, The functional benefits of the longterm recovery process are relatively minor and are usually reversed within a few years, Neverthel ess, it is suggested that long-term remyelination may perform an important role in protecting demyelinated axons from degeneration, Understanding the factors which promote long-term remyelination may have significant implicat ions for therapy in multiple sclerosis.