| Abstract: | Multichannel pattern reversal visual evoked potentials (PRVEPs) from full-field (FF), half-field (HF) and foveal (central-field, CF) stimulation were recorded in 112 mildly disabled multiple sclerosis (MS) patients with the aim of evaluating the contribution of HF and CF stimulation in this disease. CF stimulation was marginally more sensitive in detecting abnormalities (75% of patients) than FF stimulation (71% of patients). However, more importantly the two techniques were found to be complementary with the maximum number of abnormalities (79% of patients) resulting from a combination of the results. Abnormal FF responses were further evaluated by HF responses. P100 latency prolongation indicative of conduction delay was the most common finding but one-third of abnormalities consisted of disturbances of wave form relating to conduction block predominantly in macular fibres. Furthermore 34% of patients had an absent or indeterminate response to CF stimulation thus providing electrophysiological confirmation of the preferential involvement of macular fibres in MS. Although electrophysiological abnormalities were localised to the optic nerve in the majority of cases, some patients also had evidence of retrochiasmatic and chiasmatic lesions. In the majority of cases CF stimulation proved to be a useful alternative to HF stimulation in evaluating FF responses with abnormal wave forms. The study also suggested that an important factor determining whether a central scotoma will disturb the morphology of the FF VEP in the midline recording channel is the position of the macular representation in the occipital cortex. It is concluded that with multichannel recording and the additional use of CF and HF stimulation it is possible to increase the yield of PRVEP abnormalities found in MS and to define their nature with considerably greater precision. |
