Clinical correlation of occipital intermittent rhythmic delta activity.

Frontal intermittent rhythmic delta activity is associated with encephalopathy, and temporal intermittent delta activity is associated with epilepsy, but the importance of OIRDA (OIRDA) is less well defined. The authors reviewed retrospectively EEGs and medical records of 77 patients with OIRDA to determine whether they had epilepsy, acute encephalopathy, or another diagnosis. They compared the incidence of epilepsy in this population with a control group of 77 patients referred for EEG, matched for age, gender, and year of EEG. OIRDA was most commonly generalized, high amplitude, saw toothed, and reactive to eye opening, and with mean frequency of 2.89 +/- 0.50 Hz. Mean age was 8.1 +/- 4.5 years. Seventy-six of 77 patients were <or= 18 years old. Seizures were present in 69 OIRDA patients but only 41 control subjects (P < 0.0001). OIRDA compared with control subjects had more patients with GTCs (34 vs. 10; P < 0.0001) and absence seizures (25 vs. 6; P < 0.0001), but an equal number had partial seizures (30 vs. 27). Only one OIRDA patient had acute encephalopathy. OIRDA patients with seizures were younger (7.6 +/- 4.7 years vs. 12 +/- 6.9 years; P < 0.01) and more likely to evolve to spike-wave activity compared with OIRDA patients without seizures. OIRDA is present almost exclusively in children and is associated with epilepsy but not acute encephalopathy. OIRDA has clinical importance distinctly different from frontal intermittent rhythmic delta activity.