Electroclinical Characteristics and Prognostic Significance of Postanoxic Oral Automatism: A Case Series and Literature Review.

Background and objectives: Postanoxic myoclonus is a well-recognized phenomenon after cardiac arrest and often indicates poor prognosis. Other spontaneous movements, such as tonic eyelid opening, have also been documented, but spontaneous chewing movements remain poorly characterized. The aim of this study was to systematically analyze the electrophysiologic features of postanoxic chewing movements, propose a standardized nomenclature, discuss potential pathophysiology, and evaluate their prognostic significance.

Methods: We retrospectively reviewed clinical data from post-cardiac arrest patients who exhibited suspicious chewing movements during continuous video-EEG (vEEG) monitoring between January 2021 and December 2024. Chewing movements were analyzed for duration, frequency, and correlation with EEG findings. Demographic, clinical, management, and outcome data were also collected. A thorough literature review was conducted.

Results: Twelve patients (mean age: 62.3 ± 10.5 years) who experienced out-of-hospital cardiac arrest exhibited repetitive chewing movements. Detailed analysis of video recordings and bedside observations identified these movements as rhythmic tongue elevations against the upper palate with minimal jaw activity, producing chewing artifacts on EEG. These episodes lasted 4-5 seconds and were periodic in 2 patients. Video-EEG revealed that in 8 patients, the movements followed EEG bursts by 1-1.5 seconds, whereas in 4 patients, they occurred spontaneously without corresponding cortical activity. The movements were transient, with a median duration of 24 hours, and resolved within 72 hours despite persistent burst-suppression patterns. Brain MRI in 3 patients demonstrated diffuse anoxic/hypoxic cortical injury with relative brainstem preservation. All patients died after cardiac arrest, with a median survival of 5 days.

Discussion: We propose the term postanoxic oral automatism (PAOA) to describe a distinct, transient oral motor phenomenon characterized by repetitive, chewing-like tongue movements in comatose patients after cardiac arrest. Unlike previous reports confined to burst-suppression EEG patterns, our findings show that PAOA can occur in both burst-suppression and background-suppression EEG backgrounds. These movements likely result from disinhibition of brainstem central pattern generators responsible for rhythmic orofacial activity and may signify severe cortical dysfunction. Although PAOA is associated with poor prognosis, its independent predictive value remains unclear.