Clinical electroencephalography in a psychiatric service.

An audit of the use of clinical electroencephalography in a psychiatric service was carried out by examining the referrals for an EEG from the service over one year (11% of all referrals), comparing them with matched patient controls, rating the EEGs blindly and estimating the clinical value of the investigation for each patient; 37% were abnormal, 19% anomalous and 44% normal. The following two clusters of symptoms and signs were associated with EEG referral--the patients with "organic" mental state phenomena and/or CNS signs; EEG usually abnormal and the patients with behavioural changes that raise the suspicion of an organic process but, taken alone, are not compelling evidence of such (for example, impulsive behaviour, acute and atypical psychoses, perceptual or behavioural phenomena of the type associated with temporal lobe epilepsy in the absence of frank complex partial seizures); EEG usually normal or anomalous. Ninety-two percent of EEGs were judged to be of clinical value; 53% positive and 39% negative. Eight percent of referrals made no contribution to the clinical evaluation.