Breach rhythm-induced asymmetric post-arousal hypersynchrony mimicking ictal EEG in coma.

Objective: To highlight the risk of misinterpreting stimulation-related EEG patterns as seizures in the ICU, and to illustrate how awakening hypersynchrony and breach rhythm can mimic a focal seizure, leading to an erroneous diagnosis of nonconvulsive status epilepticus (NCSE). Method: A single patient case observation of a 17-year-old male with a severe traumatic brain injury, resulting in a left depressed skull fracture and coma. A continuous EEG was analyzed during repeated auditory/somatosensory stimulations. Pharmacologic reactivity was assessed with IV clonazepam. Results: Several episodes of awakening hypersynchrony were initially misinterpreted as subclinical focal seizures, leading to a diagnosis of NCSE. The EEGs displayed asymmetrical, sharply contoured rhythmic delta waves after stimulations, showing evolution and lasting more than 10 s. These delta waves demonstrated reactivity to IV-clonazepam, resulting in an improved EEG. Although no clinical improvement was observed, the patient returned to sleep immediately. The EEGs were reinterpreted as representing arousal reactions during the awakening process. The asymmetry of the rhythmic delta waves corresponded to a breach rhythm. Conclusion: In comatose or sedated ICU patients, stimulation-induced rhythmic delta waves with apparent evolution, and even benzodiazepine responsiveness, may represent normal arousal phenomena amplified by a breach rhythm rather than ictal activity.