Non-invasive EEG evaluation in epilepsy diagnosis

Abstract

The EEG is an invaluable tool in the diagnosis of epilepsy which guides clinical management. It helps to determine if attacks are of epileptic origin, allows the estimation of the recurrence risk after a first seizure, aids in the diagnosis of the epilepsy syndrome and represents the gold standard in the presurgical evaluation of epilepsy. The EEG can also detect subclinical seizures as a cause of coma. In this review we discuss the sensitivity and specificity of the EEG, present the EEG findings and their significance in different epilepsy syndromes including focal and generalized epilepsies and describe the application of activation procedures.

Keywords:

• EEG
• epilepsy
• focal
• generalized
• hyperventilation
• medication
• photic stimulation
• sleep deprivation

Acknowledgements

We would like to thank our patients from which the recordings shown in the figures were obtained and the EEG-technicians which performed the recordings: H Assmann, B Richstein, Y Kepenek, J Marczinscki, AL Jacob, B Sabanci, D Scholvien, S Göbel, K Wulf.

Financial & competing interests disclosure

F Rosenow has received support from, and has served as a paid consultant or speaker for Novartis, Pfizer, Eisai, UCB, GSK, Cerbomed, Desitin, Hexal and Medical Tribune. F Rosenow currently receives research support from the EU, the DFG, the ESF and the CURE-Foundation. KM Klein has received speaker honoraria from UCB and Novartis Pharma AG. He has received research funding from the DFG (KL 2254/1-1) and The University of Melbourne. HM Hamer has served on the scientific advisory board of Cerbomed, Eisai, Hexal, Pfizer and UCB Pharma. He served on the speakers’ bureau of Desitin, Eisai, GlaxoSmithKline Novartis, and UCB Pharma and received research funding from the EU, DFG, Desitin, Janssen-Cilag, GlaxoSmithKline and UCB Pharma. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Key issues

• The EEG is of high relevance to detect and discern nonconvulsive status epilepticus.

• The first EEG detects interictal epileptiform discharges (IED) in about 10–50% of the patients with epilepsy and the yield increases to 60–90% by about the fourth EEG. This contrasts with the frequency of IED in non-epileptic patients ranging from 0.5–2.5% in healthy young men to 12% in a study including non-epileptic patients of all age groups with progressive cerebral disorders. Specificity is probably lower and sensitivity higher in children as compared to adults.

• Isolated IED over the temporal region as well as temporal intermittent rhythmic delta activity are strongly correlated with a clinical diagnosis of temporal lobe epilepsy (TLE). Adult patients with hippocampal sclerosis have greater than 90% of their IED in the anterior temporal region.

• In frontal lobe epilepsy, interictal EEG reveals spikes or sharp waves in 60–80%, which is less than in TLE, and IED tend to have less localizing value in frontal lobe epilepsy than in TLE because they can be bilateral, lateralized or even generalized including secondary bilateral synchrony.

• Due to fast propagation, the most frequent IED in occipital lobe epilepsy are spikes and sharp waves in temporal or temporo-occipital regions. Widespread and bilateral IED including secondary bilateral synchrony are common, and isolated epileptiform activity restricted to the occipital lobe is infrequent.

• The generalized spike-wave complex usually with a frontal maximum and a frequency range of 2–5 Hz is the hallmark of generalized epilepsies. In symptomatic epilepsies and epileptic encephalopathies, the slow-spike-wave complex (≤2.5 Hz) is a characteristic feature, whereas in the genetic generalized epilepsies without encephalopathy, frequencies between 3 and 5 Hz are the rule.

• Activation methods increase the sensitivity of the EEG in the diagnosis of epilepsy. Hyperventilation and photic stimulation increase the sensitivity only in generalized epilepsies. Sleep and sleep deprivation are effective in both focal and generalized epilepsies.

Notes