ERPs in multiple sclerosis

Involvement of cognitive functions is detectable in about 50% of patients with multiple sclerosis (MS). One important element seems to be the interruption or temporal distortion of the cross-talk among cortical associative areas and between cortical and subcortical structures as a consequence of demyelination and axonal degeneration, as occurs in the so-called subcortical dementias. There is a general agreement among recent studies that P300 latency is prolonged and amplitude is reduced in MS. Altered scalp topographic distribution is also frequent. Similar results were found in 54 MS patients. Both early and late components resulted prolonged as observed in subcortical dementia. P300 abnormalities were correlated with neuropsychological findings and magnetic resonance imaging evidence of confluent periventricular lesions. Topographically, P300 was significantly decreased in amplitude over central-anterior regions. Considering the functional aspects of cognitive dysfunction, 30 definite MS patients were studied by positron emission tomography. All patients with metabolic thalamic involvement had P300 abnormalities. Moreover, in the abnormal P300 group, significant hypometabolism was found in thalamic and in temporo-parieto-occipital regions. These results suggest that impairment of specific areas such as the thalamus is fundamental in the correct genesis of this wave.