Abstracts

Rationale: Pediatric Psychogenic Non-Epileptic Seizures are a common diagnosis, making up 25-40% of those seen in tertiary epilepsy centres and epilepsy monitoring units. Event capture on video EEG is often needed for a definitive diagnosis, causing delays in appropriate treatment. While PNES occurs in a “healthy” nervous system, physical differences exist between those with PNES and healthy controls; often relating to increased activation of the nervous system. Hyperventilation (HV) during an EEG is a standard protocol used to exacerbate or trigger seizures in patients with epilepsy. Interestingly, it is also known to precipitate non-epileptic seizures in patients with PNES and it may be that a similar mechanism of activation occurs.

Methods: This was a retrospective study on 89 patients between the ages of 6-18 separated into three cohorts: 1. PNES, 2. Generalized Epilepsy (GE), and 3. Healthy Controls. Using Persyst 12 Software, a Fourier Fast Transform Spectrum Analysis was used to decompose the raw EEG signal into the absolute power within the standard EEG frequency bands (delta – 0.5-4 Hz, theta- 4-8 Hz, alpha – 8-12, beta 12-30 Hz). These data were then averaged over the following time points: 1-minute pre-HV; 1, 2, and 3 minutes of HV; and 1, 2, and 3 minutes post-HV. The power spectra were normalized by the pre-HV levels for comparisons. Descriptive statistics, positive predictive value (PPV), negative predictive value (NPV), sensitivity, and specificity were calculated and the power spectra of the frequency bands were compared using a Mixed Anova with post-hoc Tukey comparisons run using SPSS (v. 27).

Results: In all groups, HV resulted in a significant power buildup (p< 0.001) at all frequencies (Figure 1A-C). Following HV, the power spectra returned to or even below pre-HV levels within 3 minutes, with one exception: in the PNES cohort, power in the beta band remained elevated above the pre-HV levels throughout post-HV recovery (Figure 1 D). Between-group comparisons showed the post-HV beta elevation in the PNES group was significantly higher than in the GE and control group for the 6-9 age group (p=0.013, p=0.003, respectively), the 10-14 age group (p=0.002, p=0.009) and the 15-18 age group (p=0.033, p=0.003). A post-HV beta elevation of >20% is strongly associated with PNES, with a PPV of 0.83 and a NPV of 0.95 (Sensitivity 0.87, Specificity 0.93, prevalence 0.26) among all the patients.

Conclusions: Delayed normalization of the elevated beta activity within the EEGs of patients with PNES may reflect excessive network activation and synchrony secondary to heightened attention and stress. What these data show is that a quantitative analysis of HV in a routine EEG can provide a biomarker of PNES. Combined with clinical examination and history, this may result in earlier treatment, preventing harm and expediting recovery.

Funding: Please list any funding that was received in support of this abstract.: Marvin Braun's Fellowship was supported by the Robert Haslam Chair in Pediatric Neurology.