P09-T An extraordinary EEG phenomenon misdiagnosed as nonconvulsive status epilepticus: Subclinical ictal discharges interrupted by verbal stimuli

Abstract

Background Triggering or modulation of seizures and rhythmic EEG patterns by external stimuli are well-known but an exclusive stopping effect by sound was not reported before. Here, we report a peculiar manifestation of stimulus-related ictal discharges, namely, subclinical ictal discharges interrupted by sudden verbal stimuli. Case The patient is a 20-year-old woman with recurrent febrile seizure history between the age of 4 months to one year and marked psychomotor developmental delay of unknown cause. She also had brief episodes of staring and sometimes bilateral tonic-clonic seizures. Neurological examination revealed strabismus and microcephaly. Brain MRI did not show any abnormality. At age of 8 years, self-mutilating and agitated behaviors were noted. First EEGs revealed bifrontal 2.5–3.5 Hz spike and waves with impaired background activity. Video-EEG showed frequent patterns of long-lasting (10–60 s) bilateral paroxysmal high-voltage slow waves with occasional spikes, misdiagnosed as non-convulsive status epilepticus. However, no apparent clinical change was noted by the technician, physician and mother during these subclinical ictal EEG recordings. Interestingly, these epileptic discharges were abruptly interrupted with sudden verbal stimuli. Lysosomal enzyme activities and metabolic screening tests were unremarkable. Molecular genetic investigations for ring 20 chromosome analysis and SLC2A1 gene analysis were also unremarkable. Her seizures were partly controlled with levetiracetam, valproic acid and primidone. Conclusion We report the “reverse” type of stimulus-induced, rhythmic, periodic or ictal discharges (SIRPIDS), that is stopped by the external sound in a patient with developmental delay. External modulation of ictal-appearing EEG patterns may show clues for hidden mechanisms of epileptogenesis.