The cognitive evoked potential in epilepsy patients.

The P3 component to an auditory "oddball" stimulus was compared between 30 epilepsy patients and 27 age-matched normal controls. The P3 latency was significantly increased in the patients, but an increase beyond 3 standard deviations on two trials occurred in only 10 percent of the total sample and 13 percent when the age was restricted to less than 50 years. There were no significant differences in latencies for different seizure type or anticonvulsant levels. The best relationship on neuropsychologic performance was with the Trails B test. Since the exact latency of the P3 peak is at times difficult to determine and may involve arbitrary choices, it is proposed that when the test is used for clinical diagnostic purposes of dementia, the interpretation be limited to those instances where the P300 peak is either clearly normal or clearly present but prolonged beyond 3 standard deviations from age-matched normals. In the first instance, significant cognitive impairment is unlikely while it becomes very probable in the latter instance.