Significance of interictal temporal lobe delta activity for localization of the primary epileptogenic region

Because interictal temporal lobe delta activity (TLDA) has been described i n 30 to 90% of patients with temporal lobe epilepsy (TLE) but has not been investigated in patients with extratemporal epilepsy, we sought to determin e the localizing significance of TLDA. We compared the presurgical interict al scalp EEG results of 47 consecutive patients who received extratemporal resection (40 frontal and 7 parietal-occipital) for intractable epilepsy wi th 43 consecutive patients who received anterior temporal lobectomy. We def ined lateralized TLDA as runs of lower than 4-Hz waveforms that were easily distinguished from the background rhythms and were maximal at electrodes T 4, F8, and T6 or T3, F7, and T5. The lateralized TLDA was subcategorized as temporal intermittent rhythmic delta activity (TIRDA) or temporal intermit tent polymorphic delta activity (TIPDA). A chi-square test was used to dete rmine the association of the lobe of the epileptogenic zone with TIRDA and TIPDA. We found TIRDA in 12 (28%) and TIPDA in 8 (19%) patients in the temp oral lobe group, and TIRDA in 2 (4%) and TIPDA in 9 (19%) patients in the e xtratemporal group. TIRDA was strongly associated with TLE (p < 0.003), whe reas TIPDA occurred at an equal rate in both groups. Similar to anterior te mporal epilepsy, lateralized TIPDA is present in up to 20% of patients with extratemporal epilepsy. The presence of TIRDA strongly suggests TLE but ma y infrequently occur in extratemporal epilepsy. Caution should be used when using lateralized TLDA as a presurgical localizing finding.