It can be difficult to make a diagnosis of epilepsy, and misdiagnosis is not rare . In most cases, a detailed history and a reliable account of the event by an eyewitness is sufficient to make a diagnosis, but this may not always be available. In addition, certain types of nonepileptic events can be difficult to distinguish from seizures, and certain types of seizures can be misdiagnosed as nonepileptic events .
An interictal electroencephalogram (EEG) can provide evidence that helps to confirm or refute the diagnosis of epilepsy, but has many limitations. The most helpful finding on EEG is interictal epileptiform discharges (IEDs), but this finding has imperfect sensitivity and specificity. For patients with recurrent events and nondiagnostic interictal EEG findings, or lack of response to treatment, EEG monitoring is often required to distinguish epileptic seizures from nonepileptic events (table 1). EEG monitoring can be done in the outpatient setting (ambulatory-EEG monitoring) or in the inpatient setting, with combined continuous video monitoring (video-EEG monitoring).
This topic discusses the use of EEG monitoring in the diagnosis of seizures and epilepsy. More detailed discussions of routine EEG, and the use of other diagnostic tests in the evaluation of patients with seizures and epilepsy are presented separately. The differential diagnosis of seizures is also presented separately. (See "Electroencephalography (EEG) in the diagnosis of seizures and epilepsy" and "Neuroimaging in the evaluation of seizures and epilepsy" and "Evaluation of the first seizure in adults" and "Nonepileptic paroxysmal disorders in adolescents and adults".)
Ambulatory-EEG (aEEG) monitoring allows prolonged EEG recording outside the hospital or clinic setting. The technology has evolved such that portable recordings of up to 36 channels, over several days are possible . Typically, computer software designed to detect electrographic seizures and interictal epileptiform discharges (IEDs) assists in interpretation. However, no program has high specificity and sensitivity, and prolonged segments of the study, ideally the entire study, should be reviewed in their entirety as resources allow. Patients and observers also have the opportunity to "tag" portions of the recording during clinical events using a push button device. Some systems have the added capability of simultaneous electrocardiogram, pulse oximetry, polysomnography, and/or video recording.
aEEG is less expensive than inpatient video-EEG monitoring, with costs that are 51 to 65 percent lower than a 24-hour inpatient admission for video-EEG monitoring [3,4]. However, inpatient video-EEG has several advantages that make it the gold standard test in differentiating epileptic from nonepileptic seizures. (See 'Video-EEG monitoring' below.)