Abstracts

Rationale: FIRDA is characterized by transient intermittent rhythmic delta waves in the frontopolar regions.[1] Initially ascribed to deep or midline cerebral lesions resulting in increased intracranial pressure, this pattern has since been described in various structural abnormalities and metabolic encephalopathies.[2] [3][1] Zurek R, et al. Frontal intermittent rhythmical delta activity and anterior bradyrhythmia. Clin Electroencephalogr 1985;16:1-10.[1] Daly D, et al. The encephalogram in cases of tumors of the posterior fossa and third ventricle. EEG Clin Neurophysiol 1953;5:203-16.[1] Fariello RG, et al. Neuroradiological correlates of frontally predominant intermittent rhythmic activity (FIRDA). Electroencephalogr Clin Neurophysiol 1982;54:194-202.  Methods: We present a case of transient FIRDA observed in an adult patient who underwent SEEG with recording electrodes placed in bilateral medial frontal, parietal and temporal regions. A 23 yo RH male with chronic intractable focal epilepsy underwent SEEG using the frameless robotic stereotactic assistance (ROSA). A total of 15 (1x8 contact, 0.8mm in diameter) depth electrodes were placed bilaterally, 8 on the left and 7 on the right: Fronto-polar (FP), Anterior cingulated (AS), SMA, Insula (IN), Hippocampus (HIP), Lateral temporal lobe (LT), Angular gyrus (AN), and only the left Parietal (LP) (Image 1). Results: There were 2 electrographic seizures recorded on days 3 and 4 of recording characterized by onset in the left parietal and angular gyrus with spread to the lateral temporal and anterior cingulate electrodes, and then the left hippocampal leads. Beginning on day 8, the EEG background was interrupted by trains of diffuse, intermittent, rhythmic, delta activity (FIRDA) without evolution in frequency or distribution both in wakefulness and sleep. This activity correlated with frontal intermittent rhythmic delta activity (1.5-2 Hz),  on fronto-polar scalp electrodes (Image 2). The FIRDA was less prominent by day 10 of recording and was no longer seen by day 12. No further seizures were recorded. The patient complained of cognitive slowing and difficulty concentrating during days 8-10 of recording but denied auras or seizures. His physical exam was unchanged and lab work throughout the admission did not reveal any metabolic derangements. A head CT after electrode explantation (day 12) did not reveal any acute structural abnormalities. An MRI brain done 1 week later demonstrated new foci of susceptibility in the bilateral frontal, temporal, and parietal lobes related to recent electrode placement.Four months later, the patient underwent implantation of a responsive neurostimulator with electrodes placed in the left parietal (LP) and angular gyrus (LAN) regions. Conclusions: FIRDA was transiently observed in an adult patient who underwent SEEG with recording electrodes placed in deep midline frontal, parietal, and temporal regions, without neurologic deficits or metabolic derangements. Consistent with the initial notion, this case may suggest deep midline brain networks as the generators of FIRDA. Funding: No funding