Abstracts

Rationale: Ictal central apnea (ICA) is seen in around half of patients with focal epilepsy typically before the electrographic seizure onset. ICA has been described to be more common in temporal than extratemporal epilepsy (1). The observation of ICA being a feature of epilepsies from the temporal lobe is consistent with previous human stimulation studies pointing out amygdala, hippocampus and mesial temporal pole as the symptomatogenic zone for ICA (2,3). We examine the incidence and characteristics of ICA in patients with mesial temporal lobe epilepsy (mTLE) and the apnea's relationship with the EEG seizure onset and the first clinical sign of the seizure. To our knowledge, this is the first reported study looking solely at patients with mTLE.  Methods: A retrospective review of 13 consecutive adult patients with mTLE, either confirmed by MRI and/or invasive EEG, admitted to our epilepsy monitoring unit. Video EEG, nasal airflow, thoraco-abdominal excursions via respiratory inductance plethysmography, and capillary oxygen saturation were analyzed.All patient had a clinical semiology and neurophysiologic findings congruent with mTLE. Patients with multifocal or bitemporal were excluded. Patients with multiple epileptogenic lesions that may provide ambiguity of seizure onset or dual pathology (e.g. concomitant heterotopias or diffuse cortical dysplasia) were excluded.Central apnea (absence of thoracic-abdominal breathing movements) was defined as >1 missed breath and apnea lasting >5 seconds, during non-convulsive seizures or the pre-convulsive phase of a bilateral convulsive seizure (1). Onset of ICA as compared to EEG seizure and first clinical signs were determined by looking at the first seizure in each patient during the EMU recording that had plethysmography tracings without artifact.  Results: Thirteen (females, n=8) patients were included in this study. The mean age was 44.5 [26-70] years. The incidence of ICA in the first recorded seizure was 92% (12/13 patients). Median apnea duration was 45 seconds [5-102]. ICA preceded EEG seizure onset in 46% (6/13 patients). The median time that the ICA preceded EEG seizure onset was 9 seconds [4-31]. ICA was seen before other clinical signs in 38 % (5/13 patients).77% (10/13) of patients showed hypoxemia (SpO2 <95%). 60% (6/10) and 20% of those patients had a moderate (75-89%) and severe hypoxemia (<75%), respectively. An example of an ICA preceding EEG seizure onset is provided in Figure 1.  Conclusions: Ictal apnea characteristics in our cohort are consistent with the findings previously reported in the literature about temporal lobe epilepsies (1). Patients with unilateral mesial temporal lobe epilepsy (e.g. hippocampal sclerosis) have a high incidence of ICA likely related to involvement of mesial temporal structures in particular the amygdala in respiratory control.ICA precedes both EEG as well as clinical seizure onset on scalp recordings in a substantial number of patients. Plethysmographic respiratory monitoring in regular clinical practice has localizing value during surface recordings associated with mTLE. It appears paramount to monitor respiration during invasive recording to confirm that the recorded intracranial seizure onset precedes onset of the first clinical signs.Limitations of our study include the observational and retrospective nature of a study in a small select group of patients (i.e., lesional mTLE). Breathing analysis through polygraphic recordings was limited to thoraco-abdominal movement and measurement of nasal airflow which is often subjected to multiple types of artifact, including from movement, talking, eating, which may prevent the detection of ICA and underestimate the incidence.(1) Vilella L, Lacuey N, et al. Incidence, Recurrence, and Risk factors for peri-ictal Central apnea and sudden unexpected death in Epilepsy. Front. Neurol. 2019; 10:166(2) Lacuey N, Hampson JP, et al. Limbic and paralimbic structures driving ictal central apnea. Neurology 2019 11:10.1212(3) Nobis W, Schuele S, et al. Amygdala-Stimulation-Induced Apnea is Attention and Nasal-Breathing Dependent. Ann Neurol 2018; 83:460-471  Funding: National Institute of Neurologic Disorders and Stroke (NINDS) Centers without Walls for Collaborative Research in Epilepsy: SUDEP (UO1). Grant No: RFA-NS-14-004