"Periodic" seizures

To describe regularly recurring ictal phenomena as recorded in a single patient whose seizure disorder related to a left temporal cavernous angioma.

Seizures were recorded by left temporal subdural strip electrodes which were bilaterally placed because of ambiguous seizure origin and right temporal memory dysfunction at Wada testing. Seizure length, interseizure intervals, and interseizure onset intervals were visually assessed. The coefficient of variation was used as an estimate of variability in seizure periodicity.

Mean seizure durations varied from 68 to 95 s; coefficients of variation varied from 0.08 to 0.18, values similar to other periodic biological phenomena. Mean daily seizure intervals varied from 96 to 152 s with coefficients of variation ranging from 0.12 to 0.35. Interseizure onset intervals had smaller coefficients of variation (0.03-0.20). Manifestations of these simple partial seizures included a rising epigastric sensation and nausea.

Previously described periodic EEG phenomena are interictal events or appear with peripheral events of similar cadence. Therefore, we remain unaware of any documentation of periodic ictal electrographic events. The restricted propagation and duration of these recorded seizures may have simplified their pathophysiology allowing a stereotyped involvement of excitatory and inhibitory mechanisms producing the periodicity.