Abstracts

Rationale: Previous studies show the best estimate of non-convulsive seizure (NCS) prevalence is 8% in comatose patients⁸and 10-19% in ICU patients.^1,3,7 Delayed treatment of NCS may lead to an increase in mortality up to 85% if duration exceeds 20 hours.¹⁰ Refractory NCS such as non-convulsive status epilepticus (NCSE) may cause permanent neuronal damage via an increase in extracellular brain glutamate leading to brain swelling and apoptosis.⁹ The diagnosis of NCS requires continuous EEG (cEEG) availability and a high clinical suspicion of diagnosis. The diagnosis can be easily missed without cEEG, and may result in deleterious outcomes.^6,5 It is important to assess risk factors for NCS in patients presenting with AMS and to recognize when to obtain cEEG.Methods: Adult inpatients older than 18 years of age who received cEEG for more than 6 hours at our hospital for the indication of AMS between January 2006 and December 2009 were identified through the cEEG log. Anoxic patients undergoing induced hypothermia were excluded. NCS was defined as ictal episodes recurrent for at least 30 minutes without improvement in clinical status.^2,4,6 The following data was collected: age, sex, admission service, total duration of cEEG, time from EEG to detection of NCS, EEG patterns, degree of AMS, MRI/CT studies, use of AEDs, concurrent medical or neurological conditions, and eventual outcome. Results: NCS was detected in 67 of 281 or 24%; the prevalence was higher in neurosurgical and neurology services (74% combined or 50/67) compared to others. 69% (47/67) of NCS were seen in ICUs. Patients with NCS were more likely to have worse mental status with over 70% being stuporous or in a coma vs less than 50% of non-NCS patients. Patients with NCS were more likely to have a history of seizures (43%,p=0.02), intracranial tumors (30%,p=0.07), craniotomy (34%,p=0.05) (table 1). More than 90% of the patients had an MRI or/and CT. Over 50% of the NCS population showed imaging evidence of increased intracranial pressure or mass effect (p<0.001). Bilateral parietal or temporal abnormalities (as opposed to unilateral) were more than twice as frequent in NCS than non-NCS populations (table 2). of patients had an improvement in alertness to baseline while the other half died. Mean total duration of cEEG was 48 hours in NCS and 24 hours in non-NCS populations. 73% had detection of NCS within 1 hour of cEEG; Within 24 hours of cEEG, 96% of NCS diagnosis were established.Conclusions: In this study, we found prevalence of NCS in inpatients adult populations with AMS to be 24%, higher than previously reported values. As expected, the rate was increased in the ICU environment. Identified risk factors are history of seizure disorders, recent craniotomy, and aggressive intracranial tumors such as GBM. Imaging evidence of mass effect, increased intracranial pressure and bilateral parietal/temporal abnormalities may also increase risks. Mortality associated with NCS is high; however, this may depend on underlying etiology. Minimum of 24 hours of cEEG is required for an evaluation of NCS. Further prospective study to confirm these findings is warranted in the future.