Abstracts

Rationale: EEG patterns seen to be induced after various tactile or even auditory stimuli were first described by Hirsch et al. in 2004 and they have been commonly found in patients undergoing continuous EEG monitoring. Despite ongoing investigations, the pathophysiology, therapeutic and prognostic significance of stimulus-induced rhythmic, periodic or Ictal discharges (SIRPIDs) continues to be complicated and unclear how it applies to specific pathologies. We aimed to investigate the clinical implications of a specific cohort of patients with acute brain injury excluding anoxic brain injury.

Methods: We conducted a single center, institutional review of 403 hospitalized patients in both the ICU and non-ICU settings from May 2016 to August 2017. The study was approved by the Massachusetts General Hospital Institutional Review Board. We included patients above the age of 18 and who received an EEG recording of 2 or more hours during a single admission. Patients who were monitored for cardiac arrest while in the hospital were excluded from the study. Demographic data including age, gender, primary admitting diagnosis, GCS score on admission, history of epilepsy, hospital length of stay, in hospital mortality, and discharge location and MRS at discharge. EEG recordings were obtained using the international 10-20 system and were reviewed for the best background activity and unilateral vs focal slowing, presence of sleep architecture, sharp waves, generalized periodic discharges, lateralized periodic discharges, generalized rhythmic delta activity, lateralized rhythmic delta activity, bilateral independent periodic discharges, seizures (electrographic and clinical) and SIRPIDs. If a cEEG was documented to having SIRPIDs, further data were collected to ascertain which type of SIRPIDs were present (i.e., SI-GPD, SI-LPD, SI-GRDA, SI-LRDA, SI-BIPD, SI-Seizures). 

Results: Total of 351 patients were included in the final analysis. SIRPIDs were identified in 82 patients (23.4%). Median age was 70 years (IQR, 60-79) and 49 (60%) were females. Patients with SIRPIDs had a median initial GCS of 12 (IQR, 6-15) and a length of stay of 12 days (IQR, 6-15). Twelve (15%) patients with SIRPIDs had the presence of a posterior dominant rhythm (PDR), thirty-one (38%) had reactivity other than SIRPIDs response and fifteen (18%) had sleep architecture. Among SIRPIDs patients, twenty-four (29%) had a burst suppression pattern and thirty-two (39%) had either a clinical or an electrographic seizure independent of SIRPIDs. On univariate and multivariate analyses, female gender, history of hypertension and history of epilepsy correlated with the presence of SIRPIDs. The presence of SIRPIDs was also associated with in-hospital mortality (OR 2.84 [1.58 - 5.09]  p=0.0007) and poor outcome classified as MRS 5 or 6 (OR 4.75  [2.74 - 8.24]  p=< 0.0001).