Nonconvulsive Status Epilepticus: Validating the Salzburg Criteria Against an Expert EEG Examiner.

Purpose: Rapid and correct diagnosis of nonconvulsive status epilepticus (NCSE) is crucial for optimal treatment. However, electroencephalographic diagnosis can be challenging. Salzburg Consensus Criteria (SCC) have been proposed to facilitate correct diagnosis, but their validity needs to be further established.

Methods: We retrospectively reanalyzed the first EEG in adult patients (n = 284) referred under the suspicion of NCSE at our institution in 2014. Nonconvulsive status epilepticus or possible NCSE was diagnosed according to the SCC by an examiner specifically trained in SCC and was compared with the original diagnosis made by an expert EEG examiner, which in this context served as the reference standard, to assess the validity of the criteria. Furthermore, the clinical outcome for patients not diagnosed using SCC (false-negatives) was examined.

Results: Nonconvulsive status epilepticus or possible NCSE was diagnosed in 40 patients by the inexperienced reader using the SCC, blinded to other clinical data, and in 47 patients by the experienced reader, not blinded to the clinical data, who did not use SCC. There were eight false-negatives, one false-positive, 39 true-positives, and 236 true-negatives. Concordance between SCC and the reference standard was high (k = 0.88 [95% confidence interval, 0.80 to 0.96]). Four of the eight false-negatives suffered from anoxic encephalopathy. The remainder had a history of epilepsy and returned to preictal functional state.

Conclusions: The SCC for NCSE implemented by an inexperienced EEG reader, blinded to all other data, yielded results highly concordant with the evaluation of EEG by an experienced reader. False-negative diagnoses were associated with postictal states or anoxic encephalopathy.