A prospective study of the predictive value of electroencephalographic abnormalities for epileptic loss of consciousness.

Patients referred to a neurology clinic with their first episode of loss of consciousness were studied prospectively in order to clarify the positive predictive value of an epileptic EEG for establishing an epileptic cause of the loss of consciousness. The clinical diagnosis was categorised as epileptic or non-epileptic. The EEG was reported as epileptic or non-epileptic, but abnormal or normal, according to recognised criteria. Patients were followed for a period ranging from 1 to 18 months to assess the accuracy of the original diagnosis. A total of 38 patients were available for analysis. Thirteen patients had a clinical diagnosis of epilepsy and 25 patients had a non-epileptic diagnosis. Five patients with an epileptic history had an epileptic EEG and 2 patients with a non-epileptic history had an epileptic EEG. Non-epileptic EEG abnormalities were present in a further 4 patients with a non-epileptic history. Follow-up was achieved for 53% of patients and in none of these was the final diagnosis different from the initial one. The positive predictive value of an epileptic EEG for a diagnosis of epilepsy was 71%, and the negative predictive value of a normal EEG for a diagnosis of non-epilepsy was 74%. The positive predictive value for any abnormality in the EEG for a diagnosis of epilepsy was 45%, and the negative predictive value of an absence of any abnormality in the EEG for a diagnosis of non-epilepsy was 70%.(ABSTRACT TRUNCATED AT 250 WORDS)