Provocative test for early diagnosis of multiple sclerosis.

A new provocative test for early diagnosis of Multiple Sclerosis (MS) is presented. It is based on the recording of pattern visual evoked responses (VER) before and after exposing patients to a high luminance background. All 13 patients tested showed a biphasic enlargement of the P100 wave after bleaching even in the absence of an increased P100 latency. This biphasic enlargement can be interpreted as a fatigue or a saturation-like phenomenon as can be seen psychophysically. The saturation-like effect involves probably only affected fibers. No change in the VER was observed in 20 Normal observers examined in the same way. This test can be usefully employed in dubious cases of MS where routine VER do not provide reliable results.