Significance of epileptiform discharges in patients without epilepsy in the community

To determine the frequency of recording epileptiform discharges (EDs) in patients without epilepsy in the community and to assess their risk of seizure disorders subsequently developing.

We identified all outpatient and inpatient EEGs that were recorded in persons residing in Rochester, Minnesota, from 1979 to 1988. Patients with a history of unprovoked seizure disorders before the index EEG were excluded. Periodic lateralized EDs (PLEDs) were not evaluated, because of their well-established association with seizure disorders.

Five hundred twenty-one patients in the community had no history of unprovoked seizure disorders before their EEG. Sixty-four (12.3%) patients had EDs; neither isolated unprovoked seizure nor epilepsy developed during 230.8 person-years of follow-up. Forty-seven (73.4%) of the 64 patients had acute or progressive cerebral disorders when EEG detected EDs. Seizures that were acutely provoked by the underlying disorder (enlarging brain tumor, cerebral infarct, or bilateral subdural hematoma, in one patient each) subsequently developed in three (6.3%) of the 64 patients. Seizures of any type did not develop in the 17 patients without acute or progressive cerebral disorders.

In a community setting, EDs are sometimes observed in patients without epilepsy. However, nearly three fourths have underlying acute or progressive cerebral disorders. Acutely provoked seizures may develop in a small proportion of patients. Although none of our patients developed isolated unprovoked seizures or epilepsy, a longer period of follow-up is needed to determine their risks relative to the general population.