CT-measured optic nerve sheath diameter distinguishes PNES from epileptic seizures in the emergency department

To evaluate the discriminative value of optic nerve sheath diameter (ONSD) measured on non-contrast brain CT in adults presenting to the emergency department (ED) with generalized tonic-clonic seizure-like complaints and subsequently diagnosed with epileptic seizures or psychogenic nonepileptic seizures (PNES).

This single-center, retrospective study included 89 adults (40 epileptic seizures, 49 PNES) who presented to the ED with a first-time seizure-like complaint and had no prior documented history of epilepsy or antiseizure medication use at presentation. Final diagnoses were established after ED discharge based on neurology evaluation (and psychiatry when indicated), clinical semiology, and routine interictal EEG in the absence of long-term video-EEG availability. ONSD was measured by two independent emergency medicine specialists on the index non-contrast CT as the transverse diameter approximately 3 mm posterior to the globe using a standardized reconstruction series and viewing parameters.

Mean age was 42.7 ± 16.4 years and 51.7% were female. Mean ONSD was 5.91 ± 0.78 mm in the epileptic seizure group versus 4.82 ± 0.72 mm in the PNES group (p < 0.001). An optimal mean ONSD cutoff of 5.43 mm yielded 85.0% sensitivity and 85.7% specificity (AUC=0.848).

In adults presenting to the ED with seizure-like complaints, CT-derived ONSD may support early differentiation between epileptic seizures and PNES as an adjunctive parameter obtained from imaging performed for standard clinical indications. ONSD should not be used as a stand-alone diagnostic test and should be interpreted alongside clinical assessment, EEG/video-EEG when available, and psychiatric evaluation, with external validation required before routine threshold adoption.