Increasing the Yield of EEG

Abstract

The EEG is the most common neurodiagnostic test performed to evaluate patients with suspected seizures. The majority of EEGs are requested in patients because of suspected seizures or for seizure management. It is unlikely that the patient's usual spell will be recorded during a routine EEG. Therefore, several activation techniques have been used in clinical EEG to help increase the occurrence of interictal epileptiform abnormalities, which are highly correlated with the diagnosis of a seizure disorder. EEG laboratories have long employed these techniques, which include hyperventilation, intermittent photic stimulation, sleep, and sleep deprivation. However, despite being utilized in routine clinical EEGs for decades, a number of differing views on the usefulness and indications for these procedures exist. This review will evaluate these procedures and review their history, technique, effectiveness, controversies, and unanswered questions.

The efficacy of routine hyperventilation for seizure activation during prolonged video-electroencephalography monitoring

“…7 Similarly, in other reports that compared patients who have epilepsy with and without intracranial tumors, the activation of focal interictal activity during routine EEG was demonstrated in 6% to 9% of patients following HV. 8,9 In the study by Gabor et al, the subpopulation of patients defined by focal discharges on EEG showed an activation effect by HV in 6% of patients. 10 Compared to our study, the above reports demonstrated a relatively higher number of events during HV.…”

“…6,8 One needs to be aware of the appearance of HV-induced high-amplitude rhythmic slowing with altered awareness, which mimic absence seizures but are a different and characteristic EEG finding. 13 Similarly, overinterpretation of EEG during HV is well recognized, as reported by Benbadis and Tatum.…”

“…4 HV has also been shown to cause focal and generalized slowing on EEG, with a frequency of 20% and 13.6% of EEGs showing diffuse and lateralized slowing, respectively. 8 This slow activity has been attributed to synchronous activity in non-specific thalamocortical projecting systems, which have been abolished by lesions of the thalamus. 17,18 HV-induced slowing has been reported as a source of overinterpretation of EEG as epileptiform activity.…”

Combined electrophysiological and biosensor approaches to study purinergic regulation of epileptiform activity in cortical tissue

“…Furthermore, this adenosine tone can also be reduced by hypocapnia, which promotes seizure activity in hippocampal slices (Dulla et al, 2005). The fact that hyperventilation-induced hypocapnia is used to provoke seizures as a diagnostic test (Mendez and Brenner, 2006) and enhance electroconvulsive seizures, as are A1 receptor antagonists such as caffeine, theophylline and aminophylline (Loo et al, 2010), strongly suggests an important tonic inhibitory role for endogenous adenosine in the regulation of human seizures. Moreover, successful attempts to terminate human epileptic seizures, even after their initiation, have been made using 5 % CO2 inhalation (Tolner et al, 2011).…”

A New Method for Quantification and Assessment of Epileptiform Activity in EEG with Special Reference to Focal Nocturnal Epileptiform Activity

“…EEG is mainly used in repeated brief recordings, typically lasting 20 minutes, resulting in short samples for assessing brain functions in disease and especially in epilepsy Mendez and Brenner, 2006;Noachtar and Rémi, 2009). However, there is an increased use of long-term EEG monitoring (LTM), lasting hours or days, often with synchronous video recording.…”