Abstracts

Rationale: Electroencephalographic reactivity (EEG-R) is commonly assessed in patients with disorders of consciousness. The 2021 American Clinical Neurophysiology Society (ACNS) guidelines categorize EEG-R as reactive, unreactive, or stimulus-induced rhythmic periodic, or ictal appearing discharges (SIRPIDs)-only, but without any other qualifiers to describe in detail. EEG backgrounds of healthy adults exhibit faster (e.g. theta-alpha) frequencies in the awake/stimulated state, and slower (e.g. delta-theta) frequencies in the asleep/resting state. In contrast, limited studies have shown that some sedating medications can contribute to an EEG pattern of increased slower frequencies upon stimulation. Here, we present and characterize a separate population of reactive EEGs marked by this “atypical” pattern without sedating medications that may affect the EEG background.

Methods: We retrospectively reviewed the records of adult patients with continuous EEG performed at a single center between 7/2015-6/2022. Patients whose EEG-R were described as neither “good” nor “absent”, and with increased slower frequencies were identified. Two authors reviewed their raw EEGs and collected data related to patient demographics, hospitalization, and EEG recording.


Results: Seventy patients with “atypical” EEG-R in absence of sedating medications were identified. Median age was 59 years, 50% were female, and 60% had prior neurological histories. The indication for initial hospitalization was primary neurological in 53% (most commonly ICH), non-neurological in 40% (most commonly infection), and a combination in 7%; 26% also had secondary clinical seizures. Continuous EEG monitoring was performed to evaluate altered mental status (71%) or episodes concerning for seizures (29%), most commonly ordered by intensive care units (79%). EEG monitoring lasted a median of 1.6 days. Relevant medications included anti-seizure medications (90%), opioids (46%), cefepime (26%), and dexmedetomidine (16%). The acute medical conditions during EEG included intracranial lesions (66%), infection (63%), kidney injury (40%), hepatic dysfunction (16%), other toxic/metabolic dysfunction (47%), and intubation (43%). The awake EEG background consisted of delta-theta (93%) or delta-only (7%) frequencies, compared to the sleep background of theta-delta (67.1%), delta-theta (31.4%), or theta (1.4%). The “atypical” reactivity was marked by increased semirhythmic delta and decreased faster frequencies (60%), increased semirhythmic delta activity only (34%), or increased semirhythmic delta and theta activity but no other faster frequencies (6%). Concurrent SIRPIDs were present in only 46%. The 30-day outcome included discharged alive (54%), remain hospitalized (33%), or death (13%), with 86% survival at hospital discharge.


Conclusions: We hereby propose an addition to the ACNS terminology, called “atypical” EEG-R, characterized by increased delta activity with or without diminished faster frequencies, which can be a marker of encephalopathy. Patients with this EEG-R pattern often have toxic/metabolic pathologies with good prognosis.


Funding: None