Epilepsy Clinical Trial
Official title:
Clinical Validation of Criteria for Identification of Epileptiform Electroencephalography Discharges in Sensor Space and Source Space
Electroencephalography (EEG) records electric activity of the brain using electrodes placed
on the scalp. EEG is an important tool in the diagnostic work-up of patients with epilepsy.
Specific types of sharp EEG discharges (epileptiform discharges) are associated with patients
with epilepsy.
The International Federation of Clinical Neurophysiology (IFCN) has recently published a set
of six operational criteria for identifying epileptiform discharges. At least four criteria
need to be present in order to classify a discharge as epileptiform. These criteria are
largely based on expert opinion and have not been validated yet. It is not clear what the
sensitivity and specificity of these criteria are, and which combination of these criteria
are optimal. Each criterion is based on visual assessment. However, it is not known what the
inter-rater agreement of these criteria are.
EEG is traditionally inspected in sensor space, i.e. in the recording channels. Advances in
signal analysis made possible reconstructing the electric currents in the regions of the
brain generating them, and displaying the signals in the source space, instead of the sensor
space.
The objectives of this study are: to determine the inter-rater agreement of the IFCN criteria
by visual analysis in sensor space, to determine the combination of criteria with the best
accuracy (sensitivity and specificity) and assess the accuracy of evaluating the discharges
in source space.
The raters will analyze EEG recordings from 100 patients, from two groups: consecutive
patients with epilepsy and consecutive patients with non-epileptic paroxysmal episodes. EEG
was recorded during long-term video-EEG monitoring. As reference standard, the investigators
used the evaluation of the patients´ habitual clinical episode. The performance of the
criteria in sensor-space and the analysis in source space will be compared with the
unrestricted expert scorings.
Epilepsy affects 50 million people of all ages. It is the most common neurologic disorder
across the lifespan, and has been found to be associated with an increased risk of mortality
compared to the general population.
EEG is an important tool in the diagnostic work-up of patients with suspected epilepsy. The
presence of epileptiform EEG discharges (EDs) confirm the diagnosis and provides important
information that helps in classifying epilepsy.
EDs are visually identified by experts with training in reading EEG. Although EDs were
defined in the previous edition of the IFCN glossary of terms, that definition was
conceptual, and the inter-rater agreement for identifying EDs was only moderate. Recently,
the IFCN suggested the following operational definition for EDs: Transients distinguishable
from background activity with a characteristic morphology; EDs have to fulfill at least 4 of
the following 6 criteria:
1. Di- or tri-phasic waves with sharp or spiky morphology (i.e. pointed peak).
2. Different wave-duration than the ongoing background activity: either shorter or longer.
3. Asymmetry of the waveform: a sharply rising ascending phase and a more slowly decaying
descending phase, or vice versa.
4. The transient is followed by an associated slow after-wave.
5. The background activity surrounding epileptiform discharges is disrupted by the presence
of the epileptiform discharges.
6. Distribution of the negative and positive potentials on the scalp suggests a source of
the signal in the brain, corresponding to a radial, oblique or tangential orientation of
the source. This is best assessed by inspecting voltage maps constructed using
common-average reference.
However, these criteria are largely based on expert opinion. Data from clinical validation
studies are lacking, thus it is not known what the sensitivity and specificity of these
methods are. The threshold of four fulfilled criteria was arbitrary, and it is not sure
whether it yields the optimal accuracy (sensitivity and specificity). Furthermore, since each
criterion is based on visual evaluation, it is not known whether all experts would reach the
same conclusion.
The IFCN criteria were developed for identifying EDs using the traditional way of inspecting
EEG, in the channels of the recording electrodes (sensor space). However, advances in signal
analysis made possible to reproduce the electric currents in the brain regions, using a
spatial filtering method (source space).
The objective of this study are:
1. To determine the inter-rater agreement for the IFCN criteria
2. To determine the number of criteria and their combination that yields the highest
diagnostic accuracy
3. To determine the accuracy of identifying EDs in source space. Raters with experience in
clinical EEG will inspect 100 anonymized EEG samples, from consecutive patients with
epilepsy and consecutive patients with non-epileptic paroxysmal episodes. All 100
patients have a reference standard for their condition, derived from analysis of their
video-EEG recordings of their habitual clinical episode. Patients with both focal and
generalized epilepsy, as well as non-epileptic paroxysmal episodes (psychogenic
non-epileptic seizures, sleep-disorders, movement disorders, convulsive syncope) are
included.
Each EEG sample contains a sharp transient that is either epileptiform or not. EEGs were
recoded using the IFCN electrode array of 25 electrodes (including the ones in the inferior
temporal chain).
The samples were randomized twice, resulting in two series containing the same set of 100
samples, though with different codes and in different order of presentation. The raters will
inspect the two series separately. In the first session the raters will inspect samples in
sensor space, using traditional EEG montages (longitudinal and transversal bipolar; common
average) and voltage maps. For each sample, they will score the presence or absence of each
IFCN criterion. In the second session, the raters will inspect the EEG samples in source
space and voltage maps, and will conclude on the presence / absence of EDs.
The performance of these methods will be compared with unrestricted scorings based on the
experts´ evaluation.
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