Abstracts

Rationale: To describe a variant of rhythmic delta activity encountered in the critically ill and its clinical correlates; and to compare it with focal polymorphic (i.e. arrhythmic) delta activity (PDA) and lateralized periodic discharges (LPDs, also known as PLEDs). Methods: Retrospective review of urgent EEG and continuous EEG reports from 05/01/2011 to 04/30/2012 to identify patients with lateralized rhythmic delta activity (LRDA), LPDs and PDA. Recordings, medical charts and imaging studies were reviewed. Statistical comparisons were performed with the Chi2-test or the Fisher Exact t-test. EEG readers were all familiar with the new ACNS ICU-EEG nomenclature, including use of the term "LRDA". Results: We identified 27 patients (4.7% of all patients) with LRDA. Mean age was 52+/-3.5years (4mo-87years) and 11 were female. Twenty patients were admitted to an ICU and 17 were stuporous or comatose. Nineteen had a lateralizing neurological examination, always consistent with the side of LRDA. Twenty-four had a single unilateral focus, 2 had bilateral independent RDA (BIRDA) and 1 had two ipsilateral independent foci; thus, 30 different foci of RDA were identified in these 27 patients. Eighteen were located in the frontal region, eight in the temporal region and four in the posterior region; this distribution was similar for LPDs. Most commonly, runs of LRDA consisted in 1-2c/s, 50-200µV, sinusoidal or saw-tooth monomorphic non-evolving waves and lasted less than 10s, although faster frequencies (2-3/s) and longer duration (up to 1 min) were encountered. All patients except one had an acute or remote focal brain lesion. The most common etiologies were intracranial hemorrhage, ischemic stroke, subarachnoid hemorrhage and subdural hematoma and CNS inflammatory/infectious disorder. This was overall similar to LPDs and focal PDA except that acute intracerebral hemorrhage was more frequent in the LRDA group than in the PDA group (p < 0.01). Major systemic factors (infection, metabolic imbalance) were present in half of the cases. Twenty-four patients had abnormal brain imaging. Lesions involved the cortex or subcortical white matter (18), the deep white matter (9) or deep gray structures (5). In case of a single focal lesion, it co-localized in the same region as LRDA in all but two cases (17/19); one had an ipsilateral thalamic hemorrhage and another had an extensive upper brainstem hemorrhage. Focal periodic and sporadic epileptiform discharges were found in 12/27 and 7/27 patients respectively and always co-localized with LRDA. Seventeen patients with LRDA (63%) had acute seizures during their stay; this proportion was similar to that observed with LPDs/BIPDs (28/49 or 57%) but significantly higher than with PDA (14/105 or 13%; p=0.001). Conclusions: Lateralized rhythmic delta activity encountered on the EEG in critically ill patients appears to have the same clinical significance as LPDs/PLEDs, as more than half of the patients had acute seizures. Lateralized polymorphic delta has a much lower association with seizures.