Purpose: The clinical significance of occipital intermittent rhythmic delta activity (OIRDA) on the electroencephalogram has not been fully established. Recent studies suggest that this pattern occurs almost exclusively in children and is probably of epileptic origin in most cases. We sought to characterize the electrographic features and clinical correlates of occipital intermittent rhythmic delta activity.
Methods: A review of 697 consecutive pediatric electroencephalograms detected occipital intermittent rhythmic delta activity in 24 studies. Mean patient age was 7.96 years.
Results: Recent convulsions and absence seizures constituted the main indications for the study. Concomitant, independent epileptiform activity was noted in half of the cases. This activity was focal in all but one case. Conversely, in most cases of absence seizures, epileptiform activity intermixed with occipital intermittent rhythmic delta activity. Furthermore, the frequency of the occipital rhythmic discharges in studies of children with absences was generally faster (3-4 Hz) than in localization-related epilepsy (2-3 Hz). Most patients were awake when occipital intermittent rhythmic delta activity occurred. Chronic encephalopathy was seen in one child only. Analysis of neuroimaging studies in eight cases revealed no structural pathology associated with occipital intermittent rhythmic delta activity.
Conclusions: Occipital intermittent rhythmic delta activity is probably an epileptiform pattern, although it is noted occasionally in encephalopathic children. Its electrographic characteristics appear to differ between localization-related epilepsy and primary generalized epilepsy, particularly absence seizures.