[Shape changes in contrast VEP in multiple sclerosis: relation to the type of lesion].

VEP changes in MS patients are due to the demyelinating process which causes conduction alterations as well as inhibitory mechanisms. The pattern-shift VEP can show a delay of the main positivity, a diminished amplitude or/and an altered shape and duration. Concerning to series from the literature and own observations on more than 500 MS patients 4 different types of VEP alterations can be observed: 1. NPN complex with P2 delay; 2. broadening with loss of N2 and P2 delay; 3. bifid P2, P100-P135 complex; 4. deformation and dissociation with loss of P2, N105 dominance and amplitude reduction.