A practical guide for routine EEG studies in epilepsy.

Know what is not epilepsy! An electroencephalographer can do much more damage by overinterpreting than by underinterpreting an EEG tracing. Epilepsy is a clinical, not an EEG, diagnosis, but the EEG, when used appropriately, can greatly aid the diagnostic process. Use activating techniques such as hyperventilation, photic stimulation, and natural sleep. Take advantage of seizures in the laboratory--this is a unique opportunity to make a diagnosis. If the ictal event is not accompanied by an EEG abnormality, and pseudoseizures are suspected, remember that patients with hysterical epilepsy often have real seizures as well. Use the EEG to help differentiate between generalized and partial epileptic conditions, and to identify benign epileptic syndromes. These diagnoses have important prognostic and therapeutic implications. The EEG can help determine whether a patient is deteriorating due to increased seizure activity (undermedicated) or increased side effects (overmedicated). Postictal slowing must be differentiated from progressive or drug induced changes. The best candidates for resective surgical therapy are otherwise healthy young adults with medically intractable partial complex seizures, no psychosis, and unilateral or bilaterally independent interictal anterior temporal EEG spike foci. Patients with multifocal or bilaterally synchronous interictal EEG spikes combined with mental retardation are less likely to benefit from resective surgery, although they may be helped by corpus callosum section.