Measuring evoked responses in multiple sclerosis

Evoked potentials (EPs) have been widely utilised in Multiple Sclerosis (MS ) patients to demonstrate the involvement of sensory and motor pathways. Th eir diagnostic value is based on the ability to reveal clinically silent le sions and to objectivate the central nervous system damage in patients who complain frequently of vague and indefinite disturbances which frequently o ccurs in the early phases of the disease. The advent of magnetic resonance imaging (MRI) techniques has greatly reduced the clinical utilisation of EP s, which is not fully justifiable, as the information Provided by EPs are q uite different from those provided by MRI. The abnormalities of evoked resp onses reflect the global damage of the evoked nervous pathway and are signi ficantly correlated with the clinical findings, while the vast majority of MRI lesions ore not associated to symptoms and signs. Transversal and longi tudinal studies have demonstrated that EP changes in MS ore more strictly r elated to disability than MRI lesion burden. On the contrary MRI is more se nsitive than EPs in revealing the disease activity Evoked responses modific ations observed in MS ore not disease-specific moreover longitudinal studie s showed latency and morphology changes of evoked responses not always rela ted to clinical changes. Such a dissociation con be explained both by techn ical factors and by subclinical disease activity To reduce the negative imp act of technical aspects, only reproducible Parameters of the evoked respon ses should be used to monitor disease evolution and therapeutic interventio ns.