Clinical significance of focal topographic changes in the electroencephalogram (EEG) and evoked potentials (EP) of psychiatric patients.

The relationship between psychiatric symptoms that respond to anticonvulsants and epileptic activity is still debated. Evidence linking electroencephalographic changes to treatment response is scarce and controversial, partly because of the poor scalp representation of limbic electrical activity. We studied the clinical relevance of focal topographic changes in the resting EEG, the visual evoked potential and the P300 response in 90 psychiatric patients, by evaluating response to anticonvulsants and development of neurological complications. The group with focal changes was compared to a group with epileptiform activity but no focal changes and a group with normal or diffusely altered EEG. Focal EEG and EP changes predicted good response to anticonvulsants, while the presence of epileptiform activity did not. Clinical seizures developed only in patients with focal changes and no anticonvulsants medication. Structural abnormalities and selective neuropsychological deficits were seen only in the focal group. There was an association of symptom type and the site of focus. We concluded that focal EEG and EP changes in psychiatric patients have important theoretical as well as practical implications.