Sensitivity and specificity of the Salzburg EEG criteria for nonconvulsive status epilepticus

The Salzburg EEG criteria for nonconvulsive status epilepticus (NCSE) have been proposed as consensus criteria for NCSE. We aimed to perform an independent study of their diagnostic accuracy.

A prospective study was carried out at Oslo University Hospital, including all consecutive patients ≥15 years old who were referred for an EEG with an explicit or implicit question of NCSE from February 2020 to February 2022. Two independent EEG readers scored the included EEGs according to the Salzburg criteria and blinded to the clinical data. The reference standard was defined as the clinical diagnosis the patient received based on all available clinical and paraclinical data. Diagnostic accuracy in identifying "certain/possible NCSE" was assessed by calculating sensitivity, specificity, positive predictive value, and negative predictive value with their 95% confidence intervals.

In total, 469 patients/EEGs were included in the study. The prevalence of NCSE according to the reference standard was 11% (n = 53). The criteria showed a sensitivity of 94% (95% CI: 92-96%), a specificity of 77% (95% CI: 73-81%), a positive predictive value of 34% (95% CI: 30-39%), and a negative predictive value of 99% (95% CI: 98-100%). False positives for "certain NCSE" (n = 16) included many serial seizures and stimulus-induced rhythmic and periodic discharges (SIRPIDs), as well as a focal cortical dysplasia. False positives for "possible NCSE" (n = 79) were mainly represented by different encephalopathies and postictality.

The low specificity of the Salzburg criteria calls for refinement before implementation into daily clinical practice.