EEG in adults in the laboratory or at the patient's bedside.

Electroencephalogram (EEG) recording in the laboratory lasts at least 20 minutes and uses 19 active electrodes. It includes rest periods, stimulation procedures, a 3-mn hyperventilation period and intermittent photic stimulation (IPS). Recorded at the bedside, the EEG uses at least eight electrodes; the stimulation procedures, duration of the EEG and need to repeat the examination depend on the indication. Simultaneous video recording is recommended. The EEG report describes the basic rhythm, its reactivity and pathological activities, whether epileptic or not, and their organization. The synthetic conclusion interprets the results while taking into account the clinical context and contributes, if possible, diagnostic and/or therapeutic help in patient management. EEG performed as soon as possible after a seizure is essential for the diagnosis and initial management of epilepsy. It is helpful to characterize the epileptic syndrome in order to initiate optimal treatment. EEG is also useful in managing the withdrawal of antiepileptic drugs. EEG is also extremely useful in case of impaired consciousness, confusional state or even acute or subacute cognitive disorders. It is the only available tool able to validate the diagnosis of non-convulsive status epilepticus presenting with confusional state. EEG helps in the diagnosis of toxic or metabolic encephalopathy and can assess its severity, especially in hepatic encephalopathy. Except in rare exceptions, EEG is not routinely indicated for the evaluation of typical vasovagal syncope, headaches, dizziness, typical transient global amnesia and transient ischemic attack. EEG is irreplaceable in the diagnosis and management of certain severe and frequent pathologies involving the cerebral cortex.