title: [EEG--when and how?].
abstract: BACKGROUND
  Electroencephalography (EEG) is used for studying functional disorders of the brain. We provide an overview of the areas where EEG is most strongly indicated and the clinical benefit of the examination.
  
  
  METHODS
  This article is based on articles from personal literature archives and literature searches in PubMed, textbook on methods in clinical neurophysiology, the work of one of the authors on a new European standard for EEG and the authors' clinical experience.
  
  
  RESULTS
  EEG is primarily indicated for assessing suspected epileptic seizures and encephalopathies. Standard EEG, sleep-deprived EEG and long-term EEG examinations are used in diagnosing epilepsy. EEG will identify epileptiform activity in about 90% of patients with epilepsy. Epileptiform EEG activity in these patients will provide support for the diagnosis of epilepsy, while the absence of such activity will not exclude the diagnosis. EEG is also important for classifying the type of epileptic syndrome. In cases of encephalopathy, pathology will take the form of an increase in slow activity on the EEG and will support the diagnosis, but as a rule the EEG finding is non-specific. Findings in some cases may point to the underlying aetiology.
  
  
  CONCLUSIONS
  Electroencephalograms must be interpreted by an experienced clinical neurophysiologist or neurologist with specialist expertise in EEG interpretation, and must always be evaluated in the light of the clinical picture.
authors.affiliation: Seksjon for klinisk nevrofysiologi, Nevrosenter, Stavanger universitetssjukehus, Norway. heaien@sus.no
authors.forename: Anita
authors.initials: A
authors.lastname: Herigstad
authors.forename: Sigurbjørg
authors.initials: S
authors.lastname: Stefansdottir
authors.forename: Harald
authors.initials: H
authors.lastname: Aurlien
mesh_terms: D001927:Brain Diseases / Q000175:diagnosis; D003937:Diagnosis, Differential; D004569:Electroencephalography; D004827:Epilepsy / Q000175:diagnosis; D006801:Humans; D012640:Seizures / Q000175:diagnosis