Utilization of below-the-hairline EEG in detecting subclinical seizures

Nonconvulsive status epilepticus (NCSE) is a serious condition commonly considered when evaluating a patient with altered mental status, and an electroencephalogram (EEG) is necessary for diagnosis. Neurology house staff often must make this diagnosis at times when no EEG technologist is available. We report our experience with abbreviated, emergency below-the-hairline EEGs (BTH-EEG) performed by neurology residents at our institution over a 1-1/2 year period. We analyzed demographic and clinical data in relation to whether or not an ictal or periodic pattem was identified, and these results were compared to follow up EEGs. Thirty-nine studies were identified, ranging in duration from 3 min-13 hrs. Mean and median age of patients included was 53 (range 25-81 yrs); 21 were female. Seven of 39 BTH-EEGs showed at least one electrographic seizure, 9 more showed periodic discharges. Follow-up EEGs showed electrographic seizures in 6 of 39 patients, including 3 of the 7 with ictal BTH-EEG, and an additional 3 whose BTH-EEGs showed periodic lateralized discharges but no organized seizures. All 7 patients with ictal BTH-EEGs survived to discharge, vs. 23 of the remaining 32. We conclude that in selected cases, BTH-EEG is useful in detecting seizures and/or other epileptiform patterns. In our series, when NCSE was in question, the BTH-EEG showed these patterns 41% of the time. The BTH-EEG is a fast, non-invasive, inexpensive tool that may save valuable time, especially when no other viable option is immediately available. This technique may be applicable more broadly, not just limited to centers with neurology residents.