Abstracts

RATIONALE: Recurrent subclinical seizures represent a problematic form of epilepsy. Their clinical significance is not always apparent and when treatment is considered, clinicians lack details regarding stability of subclinical epileptiform discharges over time. Data regarding recurrence and potential for exacerbations can improve quality of care by identifying patients likely to benefit from extended followup and provide objective evidence of severity that clinicians can use in formulating treatment plans. The objective of this study was to examine serial EEGs from patients with frequent subclinical seizures and to track fluctuations in patterns of distribution and severity of discharges over time.
METHODS: We are conducting an ongoing study of acute and chronic effects of recurrent frontally predominant subclinical seizures on cognitive functions. Inclusion criteria for this study were: 1) At least two consecutive years of followup with EEGs; and 2) Frontal lobe involvement with electrographic seizures (i.e, events not accompanied by readily apparent clinical activity). Quantitative estimates of severity were obtained by determining the total amount of time/EEG with epileptiform discharges. Qualitative techniques were used to identify shared patterns of change due to small sample size and varying numbers of EEGs/patient.
RESULTS: Six patients met inclusion criteria. Followup covered 4-13 years (mean: 7 years). EEGs/patient ranged from 8-25 (mean: 14). 5/6 patients (83%) shared a primary ictal pattern of generalized 2-3 Hz fronto-temporal (FT) predominant spike and slow wave discharges (SWDs); 1/6 patients (17%) had rhythmic sharp 5-6 Hz theta involving fronto-centro-temporal regions bilaterally. 2/5 patients (40%) with 2-3 Hz FT SWDs as their primary ictal pattern presented initially with a different pattern: 8-10 Hz SWDs or 1-4 Hz SWDs. With extended followup, 4/6 patients (67%) added patterns (e.g., 25-30 Hz polyspike waves). Most EEGs (76%) had epileptiform bursts from 1-50 seconds. Ictal activity varied greatly, ranging from 0-88% of time/EEG. Using burst duration as a marker, patients were stratified into two [dsquote]tiers[dsquote]: 5/5 patients (100%) with bursts [gt]2 seconds had large fluctuations in severity while the patient with only 1-2 second duration bursts never exceeded 2% of time/EEG as nonconvulsive seizures. 3/6 patients (50%) were treated for nonconvulsive status epilepticus (NCSE) and 2/6 patients had EEGs suggestive of NCSE but cognitive deficits were not shown. The pattern of [approximately] 3 Hz SWDs worsened by hyperventilation (resembling absence seizures) suggested treatment that suppresses T-calcium type channels might help. Valproic acid or lamotrigine in 4/6 patients (67%) with these discharges did reduce SWD severity.
CONCLUSIONS: FT predominant subclinical seizures, as 2-3 Hz SWDs, persist and often recur even after near complete suppression. Extended followup with EEGs may capture changes in ictal patterns supporting specific treatment interventions. Chronic exposure to FT predominant subclinical seizures may be a risk factor for NCSE. Further studies on this issue are needed.