Hyperventilation in functional seizures: Evidence for subtypes.

PURPOSE: Functional seizures (FS) are heterogenous, with no agreed way to subdivide them. One FS subtype frequently observed during EEG is those whose seizures are provoked by hyperventilation. We wished to see whether this subtype might reflect a different seizure mechanism. METHODS: We analysed the video-EEG/ECGs of all patients with FS from two hospitals in Melbourne from 2010-6. RESULTS: We identified 120 patients during the study period, 107 of whom had usable recordings. Examining those 11 (10%) whose seizures had been induced by hyperventilation, we compared the heart rates of those where the seizure occurred during the hyperventilation, and those where they occurred afterwards. The during-hyperventilation group had a higher baseline heart rate which increased prior to their seizure; the after-hyperventilation group had a lower baseline heart rate and no pre-ictal increase. In those patients whose seizures were not hyperventilation-induced, the same two heart rate patterns could be found: those with a higher baseline heart rate showed increasing heart rate prior to seizure onset, while those with a lower baseline heart rate did not. Cluster analysis showed the sample was optimally divided into these two groups based on their pre-onset heart rate alone. CONCLUSION: Patients with FS show two distinct patterns of pre-ictal heart rate, which may reflect two distinct seizure mechanisms.

Preictal autonomic dynamics in psychogenic nonepileptic seizures.

OBJECTIVES: Psychogenic nonepileptic seizures (PNES) resemble seizures but are psychological in origin. The etiology of PNES remains poorly understood, yet several theories argue for the importance of autonomic dysregulation in its pathophysiology. We therefore conducted a retrospective study to investigate autonomic dynamics leading up to a seizure to inform their mechanistic relevance. METHODS: One hundred one patients with PNES and 45 patients with epileptic seizure (ES) were analyzed for preictal heart rate (HR) and respiratory rate (RR) at baseline and at minute intervals from 5 min to onset. RESULTS: Patients with PNES showed rising HR (p < 0.001, repeated-measures analysis of variance (ANOVA)) and rising RR (p = 0.012, repeated-measures ANOVA) from baseline to the onset of their seizures. Patients with ES did not exhibit significant preictal HR or RR increase. Patients with PNES had nonsignificantly higher preictal HR and RR than patients with ES. SIGNIFICANCE: Patients with PNES exhibit increasing autonomic arousal prior to seizure events unlike patients with epilepsy. This may reflect increasing levels of preictal anxiety, and future studies could study patients' subjective experiences of the preictal period, and more definitive measures of ventilation to see if this supported a model of PNES as "panic without panic".

The association of panic and hyperventilation with psychogenic non-epileptic seizures: A systematic review and meta-analysis.

INTRODUCTION: Psychogenic Non-Epileptic Seizures (PNES) are events that appear epileptic but are instead thought to have a psychological origin. Increased rates of several psychiatric disorders have been reported in PNES, including anxiety and panic disorders. Some theories suggest panic and/or hyperventilation have aetiological roles in PNES, though these remain unproven. METHODS: We conducted a systematic review of associations of panic and hyperventilation with PNES using Ovid Medline and PubMed, and a meta-analysis where appropriate. RESULTS: We found eighteen studies reporting rates of panic in PNES and eight studies reporting hyperventilation. The reported rate of panic attacks in PNES ranged from 17% to 83%, with physical symptoms more commonly reported, and affective symptoms less so. 'Dizziness or light-headedness' was found to be more prevalent than 'fear of dying' by random-effects meta-analysis (68% vs. 23%). A proportion meta-analysis found a weighted occurrence of 20% of panic disorder in PNES. A pooled meta-analytic rate of PNES events following voluntary hyperventilation induction was 30%, while the clinically observed rates of peri-ictal hyperventilation in PNES without induction varied from 15 to 46%. CONCLUSIONS: Previous studies have reported moderate rates of association of panic in PNES, though the proportions varied considerably across the literature, with physical symptoms more commonly reported than affective. Hyperventilation is an effective inducer of PNES events in a minority, and can be observed occurring in a minority of patients without induction. These results support an important, albeit not essential, role for panic and hyperventilation in the pathogenesis of PNES events.