Abstracts

RATIONALE: Temporal, intermittent, rhythmic, delta activity (TIRDA) is an interictal electroencephalographic pattern which has been strongly correlated with an increased risk of seizures. There has been little specific information regarding lateralization, MRI correlates or relationship to temporal, intermittent, polymorphic, delta activity (TIPDA). Therefore, we investigated these features in a large, outpatient population.
METHODS: Consecutive, adult EEGs were analyzed for the presence of intermittent rhythmic or polymorphic temporal delta activity from May 1997 to May 2001. TIRDA was defined as at least one, [gt]/=3 second interval of intermittent ([lt]80% of total record), 4 Hz activity with a predictable, regularly recurrent,temporal and morphological pattern and with maximal activity at FT9/10, F7/8, T7/8 or P7/8. TIPDA was defined as for TIRDA except for having an unpredictable, irregularly recurrent, temporal and morphological pattern.
RESULTS: A total of 4,411 EEGs were performed within a 4-year interval and reviewed. TIRDA was found in 37 patients (38 records) (0.9%). Exclusive, left-sided TIRDA was present in 26/37 (70%) patients, 9/37(24%) had right-sided TIRDA, and 2/37(6%)had bilaterally independent TIRDA. Temporal epileptiform discharges were concordant(same side as TIRDA)in 51%, discordant in 6% and absent in 43%. A single seizure or a single episode of status epilepticus was present in 5(14%) patients, 23(62%) had more than one seizure, 4(11%) had no evidence of a seizure disorder, and for 5(14%)patients there was insufficient clinical data to determine the presence of seizures. Of those patients with available clinical information, 88% had status, a single seizure or recurrent seizures. Concordant MRI lesions were present in 13 (2 tumors, 8 hippocampal sclerosis, 3 encephalomalacia) and one had a lesion contralateral to the TIRDA (hippocampal neuroepithelial cyst). Extra-temporal lesions were present in 10 patients. Normal MRIs were found in 3 patients and 10 patients did not have an MRI. Among those patients with an MRI, 48% had a concordant, temporal lobe lesion. During the same time interval 151 patients had TIPDA, of which 109(72%) were left and 42(28%) were right.
CONCLUSIONS: These findings confirm the high incidence of seizures in patients with TIRDA. A significant number of cases of TIRDA did not have a temporal lobe, structural abnormality. The finding of a strikingly asymmetric lateralization (left [gt] right) of TIRDA and TIPDA has not been previously reported. In our series, a relatively high percentage of patients did not have co-existing epileptiform discharges. This information may assist in the analysis and interpretation of EEGs showing isolated, temporal lobe, delta activity.