[The use and abuse of EEG in focal epilepsies]

For over half a century the electroencephalogram (EEG) has been and continues to be the main tool aiding clinical diagnosis, definition and classification of epilepsy, and the best means with which to orient therapy and base prognosis. The EEG is, along general lines, a diagnostic procedure that is easy to perform, low-cost and comfortable for the patient, such that it meets the criteria for frequent and sometimes excessive use, sometimes for inappropriate expectations given that the EEG has known limitations of sensitivity and specificity. Recent years have seen the development of new ways of conducting this classic neurophysiological test. We provide practical considerations on the main techniques for performing EEGs to manage patients with partial epilepsy, with reference to validation of results and protocols to follow.