Abstracts

Rationale: EEG is our best diagnostic biomarker for epilepsy, but the sensitivity of the test is low and patients with epilepsy very often have negative EEGs. In order to identify what the likely diagnostic yield would be for an EEG ordered at a new patient visit, we prospectively collected the results of clinical EEGs on new outpatients and compared the yield to the gold standard of epileptologist diagnosis. Methods: As part of an ongoing IRB approved epilepsy biomarker study at the Penn Epilepsy Center, a tertiary care referral center, all available relevant clinical data was collected on 240 consecutive outpatients. A gold standard diagnosis was determined by 3 epileptologists independently studying all available retrospective data and 6 months of prospective data including the EEG report. If there was no unanimity, the majority vote determined the diagnosis. EEG results were abstracted for inter-ictal epileptiform activity and for captured events. An EEG was considered positive if there were spikes, sharp waves, spike and wave complexes, polyspike and wave, photoparoxysmal response or temporal intermittent rhythmic delta activity. Events were considered epileptic only if the EEG showed epileptiform changes during the event. Results: 240 patients were seen from 2/2014 to 9/2015. 98 had no outpatient EEG collected in the 6 months after enrollment. 1 EEG was technically inadequate and could not be assessed. Thus, 141 patients were available for analysis. The median age of the patients was 41 (range 18-81) and 48% were female. 12% were EEGs that were longer than 1 hour, typically 24-48 hours. The epileptologists diagnosed 107 with epilepsy and 34 as having non-epileptic events. The sensitivity of the first EEG was 27% and the specificity was 100%. 43% were generalized discharges and 57% were focal discharges. There were 6 EEGs with seizures (6% of the epilepsy patient EEGs). There were 3 non-epileptic events on EEG done on non-epileptic patients (9%) and 2 non-epileptic events on epileptic patients (2%). Conclusions: In this study, the prospective sensitivity of an outpatient EEG done after an initial visit to a tertiary care referral center was 27% for epilepsy patients. In non-epileptic patients, a non-epileptic event was seen in 9% of cases. In aggregate, the EEG provided some diagnostic value for up to 32% of new patients. These values are slightly lower than a recent larger prospective study of consecutive EEGs, which showed a sensitivity for adults with a seizure-specific diagnosis of 33.6%. This could be a result of our current study having a smaller sample, but more likely reflects the inclusion of a higher average severity of epileptic seizure patients in the published sample. Funding: NIH SBIR. 1R43NS079029-01A1. Proof of Principle for a Diagnostic Blood Test of Recurrent Seizures.