The utility of prolonged outpatient ambulatory EEG

ILAE guidelines recommend the use of prolonged EEG where the diagnosis of epilepsy or the classification of the seizure syndrome is proving difficult. Due to its limited provision, video EEG monitoring is unavailable to many patients under investigation(1). The aim of this study was to examine the utility of the alternate investigation of outpatient ambulatory EEG.

In this retrospective study we analysed 324 consecutive prolonged outpatient ambulatory EEGs lasting 72-96 h (4-5 days), without medication withdrawal. EEG data and the clinical record were reviewed to investigate the utility of the investigation.

Of 324 studies: 219 (68%) studies gave positive data, 116 (36%) showed interictal epileptiform discharges (IEDs), 167 (52%) had events. 105 (32%) studies were normal. Overall 51% of studies changed management of which 22% of studies changed the diagnosis and 29% of studies refined the diagnosis by classifying the epilepsy into focal or generalised.

The present study confirms the diagnostic utility of outpatient ambulatory EEG in the diagnosis of paroxysmal events.