The Significance of LRDA With Bilateral Involvement Compared With GRDA on EEG in Critically Ill Patients.

PURPOSE

Lateralized rhythmic delta activity (LRDA) is highly associated with seizures but generalized rhythmic delta activity (GRDA; symmetric by definition) has no known seizure association. A subset of LRDA includes patterns that are "bilateral asymmetric LRDA" (LRDA-ba), falling between purely unilateral LRDA and GRDA. The significance of this finding has not been previously addressed.

METHODS

Clinical, EEG, and imaging findings were reviewed in all patients with >6 hours of continuous EEG and LRDA-ba between 2014 and 2019. They were compared with a control group of patients with GRDA, matched 1:1 for prevalence, duration, and frequency of the predominant rhythmic pattern.

RESULTS

Two hundred fifty-eight patients with LRDA-ba and 258 matched controls with GRDA were identified. Statistically significant findings included that patients with LRDA-ba were more likely to have presented with an ischemic stroke (LRDA-ba 12.4% vs. GRDA 3.9%) or subdural hemorrhage (8.9% vs. 4.3%); those with GRDA were more likely to have a metabolic encephalopathy (GRDA 10.5% vs. LRDA-ba 3.5%) or "altered mental state" without clear etiology (12.5% vs. 4.3%). Patients with LRDA-ba were significantly more likely to have a background EEG asymmetry (LRDA-ba 62.0% vs. GRDA 25.6%) or focal (arrhythmic) slowing (40.3% vs. 15.5%), and acute (65.5% vs. 46.1%) or focal (49.6% vs. 28.3%) abnormalities on computed tomography scan. Patients with LRDA-ba were more likely to have focal sporadic epileptiform discharges (95.4% vs. 37.9%), lateralized periodic discharges (32.2% vs. 5.0%), and focal electrographic seizures (33.3% vs. 11.2%); however, patients with LRDA-ba alone (i.e., without sporadic epileptiform discharges or PDs) showed only a trend toward increased seizures (17.3%) compared with a matched group of patients with GRDA alone (9.9%, P = 0.08).

CONCLUSIONS

Patients with LRDA-ba had a higher proportion of acute focal abnormalities compared with a matched group of patients with GRDA. The LRDA-ba was associated with additional evidence of focal cortical excitability on EEG (sporadic epileptiform discharges and lateralized periodic discharges) and seizures but with only a trend toward increased seizures when other signs of focal excitability were absent.