Criteria for defining interictal epileptiform discharges in EEG: a clinical validation study

Objective: To define and validate criteria for accurate identification of
EEG interictal epileptiform discharges (IEDs) using: (a) the six sensor
space criteria proposed by the International Federation of Clinical
Neurophysiology (IFCN), and, (b) a novel source space method. Criteria
yielding high specificity are needed because EEG “over-reading” is a
common cause of epilepsy misdiagnosis. Methods: Seven raters reviewed EEG
segments containing sharp waveforms from 100 patients with and without
epilepsy. Clinical diagnosis gold standard was video-EEG recording of
habitual paroxysmal events. Raters reviewed in three separate rounds, in
randomized order: 1) in sensor space, presence/absence of each IFCN
criterion was scored; 2) in source space, sharp transients were classified
as epileptiform or non-epileptiform; 3) in sensor space, sharp transients
were classified unrestricted by any criteria (expert scoring). Results:
Cut-off values of 4 and 5 criteria in sensor space, and analysis in source
space, provided high accuracy (91%, 88% and 90%, respectively), similar to
expert scoring (92%). Two methods had specificity exceeding the desired
threshold of 95%: using 5 IFCN criteria as cut-off, and analysis in source
space (both 95.65%); sensitivity of these methods was 81.48% and 85.19%.
Conclusions: Presence of 5 IFCN criteria in sensor space and analysis in
source space are optimal for clinical implementation. By extracting these
objective features, diagnostic accuracy similar to expert scorings is
achieved. Classification of evidence: This study provides Class III
evidence that IFCN criteria in sensor space and analysis in source space
have high specificity (>95%) and sensitivity (81-85%) for
identification of IEDs.