Abstracts

Rationale: Objective: To prospectively identify parameters of autonomic nervous system (ANS) which might identify seizures from pseudoseizures. Background: Distinguishing pseudoseizures from true epileptic phenomena can be difficult even in cases with constant monitoring. As dysfunction of the autonomic nervous system have been reported in patients with epilepsy we wondered if a baseline assessment of the ANS would help distinguish between these two conditions. Methods: As part of an ongoing study of ANS function in patients with epilepsy we prospectively evaluated 66 adult patients admitted for video EEG monitoring. Nine adults were excluded due to disorders that are know to affect ANS function such as diabetes and cardiac abnormalities. Of the remaining 57 patients 23 were male and 34 female (ages ranging from 18-82 years, mean=36). Baseline HR and respiratory rhythms were recorded for 5 minutes. Simple measures of heart rate variability were used. In addition spectral analysis gave low and high frequency components of cardiac variability (LF and HF). Normalized values (LFnu and HFnu) were also calculated (eg. LFnu = LF/(LF+HF)). We also looked at measures combining both heart and respiratory variability, Lfa and Rfa as calculated by ANSAR, considered to be correlates of sympathetic and parasympathetic tone respectively. Patients were categorized into event types : generalized (9), multifocal (2) or focal (13) seizures, pseudoseizures (13), spells (8) and undetermined (12). Spells were defined as non-epileptic events with an underlying physiologic basis such as myoclonus or syncope. Results: Our data showed no primary measurement to be helpful in distinguishing pseudoseizures from real seizures. However the ratio of sympathetic to parasympathetic function (LFa/RFa), and normalized LFnu showed a statistically significant increase in values in patients with real seizures compared to pseudoseizures. When focal and generalized seizures were separated, this effect was found to be specific for generalized seizures. A regression analysis using both parameters to predict pseudoseizures vs generalized seizures showed an R-Sq = 44.7% (p = .009). Conclusions: Measurement of interictal ANS tone in adult patients appear significantly effective in differentiating pseudoseizures from generalized seizures and spells. Interestingly, it was not effective in differentiating pseudoseizures from focal seizures. To our knowledge, this is the largest study of this kind to date looking at ANS and epilepsy as per the literature.