Abstracts

Rationale: Patients are frequently referred for a routine electroencephalogram (EEG) with non-specific diagnoses with the goal of determining if the index event is epileptic in etiology. We decided to review the studies of adult outpatients referred to our electroencephalography laboratory with non-specific diagnoses. Our aim was to determine the diagnostic utility of EEG to differentiate between seizures (epileptogenic abnormalities on EEG) and non-epileptic events (normal EEG study). Methods: All routine adult EEG studies with a referring diagnosis of dizziness, vertigo, black out, loss of consciousness (LOC), fall, collapse, fainting, syncope or pre-syncope over a 2-year period (1/2007-1/2009) were reviewed by a board certified electroencephalographer for the presence of epileptiform abnormalities (sharp waves or spike wave discharges). Patient history and reason for study was determined from the referring physician’s history or directly from patient at the time of the study. EEG records of patients who underwent further long-term ambulatory or inpatient video EEG monitoring were reviewed to determine how many met the final diagnosis of seizure. Results: A total of 186 patients yielded 195 routine EEGs (pre-syncope n=6, syncope n=105, black out n=16, LOC n=30, vertigo n=9, dizziness n=21, fall n=3, collapse n=3, fainting n=2). There were 139 (71%) normal routine EEGs and 56 (29%) abnormal routine EEGs. The 56 abnormal studies occurred in the following groups: 3 (50%) pre-syncope, 31 (30%) syncope, 0 black out, 9 (30%) loss of consciousness, 2 (22%) vertigo, 5 (34%) dizziness, 2 (67%) fall, 2 (66%) collapse, and 2 (100%) fainting. Nineteen of the 56 (34%) abnormal EEGs revealed epileptiform features, while the remaining 37 (66%) exhibited non-specific features (focal or diffuse slowing). Fourteen patients (7 with normal and 7 with abnormal routine EEGs) underwent further long-term EEG evaluation. Nine patients with syncope had a long-term EEG. Three out of 4 patients who had an abnormal routine EEG for syncope had a long-term EEG that revealed epileptiform features. The fourth patient had a normal long-term EEG. Four out of 5 patients with syncope who had normal routine EEGs had normal long-term EEGs. One patient demonstrated epileptiform features. One patient with LOC and a normal routine EEG underwent long-term monitoring which was normal. One patient with collapse and an abnormal routine EEG (diffuse slowing) underwent long-term monitoring which was normal. Two out of 3 patients with dizziness had abnormal routine EEGs, but all 3 had normal long-term studies. Stratifying the data according to age revealed that 27/65 (42%) patients above the age of 60 had abnormal routine EEG studies as compared to 14/69 (20%) of patients aged 18 to 40. Conclusions: Routine EEG studies are mostly normal in young patients (18-40 years of age) who are referred to the laboratory with non-specific diagnoses. Judicious use of long-term ambulatory or inpatient video EEG monitoring may increase the diagnostic yield in patients referred with the above mentioned non-specific diagnoses.