The role of the EEG in epilepsy of long duration

Although the electroencephalogram's (EEG's) relevance in the initial work-up of individuals with epilepsy is well-defined, its role in epilepsy of long duration remains uncertain. A literature survey revealed eight studies that had evaluated epileptiform patterns (EPs) in series of patients but none of these were derived from outpatients presenting for regular follow-up. Such EEG results are crucial for determining disability benefits that are often denied to people with normal records. We therefore randomly surveyed 100 adult outpatients attending the seizure follow-up clinic at Cook County Hospital. An EP was detected in 33 patients, 36 had normal records, and 31 had non-EP abnormalities. The presence of an EP was significantly related to an etiology of head injury, duration of epilepsy, age of onset before age 20 years, and receiving more than one antiepileptic drug (AED). The presence of an EP did not correlate with seizure frequency, seizure type, or presence of a neurological deficit. A prior EEG increased the proportion with an EP only to 41%. The relatively low proportion of people who demonstrated an EP suggests that (a) the presence of an EP on an EEG should not be a factor in deciding about disability benefits for individuals with epilepsy, and (b) that use of an EP as an eligibility criterion for entry into a research series is likely to generate a select group of patients, thus making it difficult to generalize results.