Objective: To describe the diagnostic value of pallidal local field potentials in distinguishing movement disorder from seizure in a complex phenotype.

Background: Sensing-capable deep brain stimulation (DBS) systems offer a unique opportunity to study patient-level patterns of abnormal, synchronized oscillations, which have been shown to play a pathological role in various movement disorders. We present a 22-year-old patient with PDE2A mutation, characterized by paroxysmal kinesigenic dyskinesia, epilepsy, and generalized dystonia, status post sensing-capable DBS of the bilateral globus pallidus interna (GPi). The patient developed phenotypically new paroxysmal events of involuntary mouth opening, neck extension, rightward head turn, and leg extension lasting one minute with decreased awareness but no loss of consciousness or urinary or fecal incontinence. Event frequency ranged from several to up to 20 daily. Determining the etiology based on semiology alone was challenging given the patient’s complex history and phenotype.

Method: The medical record was reviewed, including developmental history, genetic testing, and DBS interrogation. Two hours of baseline video electroencephalography (vEEG) was obtained, followed by simultaneous vEEG and real-time sensing of GPi local field potentials (LFP) at 14.65 Hz.

Results: Baseline vEEG demonstrated generalized background slowing, with left frontal and midline delta focal slowing, and independent sleep-activated bifrontal epileptiform discharges. There were no electroclinical events during the baseline study. Simultaneous vEEG and LFP recording captured three representative events. vEEG showed no ictal correlates despite partial loss of awareness. Each event was associated with a ~30-fold increase in LFP power at onset, followed by rapid return to baseline after clinical resolution.

Conclusion: In a patient with both hyperkinetic movement disorders and seizures, recording GPi LFPs facilitated characterization of phenotypically new events. Identifying the underlying neurophysiology was crucial in guiding therapy toward suppression of abnormal LFP bursts with single-threshold adaptive DBS. This case highlights that LFP data may be used to differentiate basal ganglia processes from cortical hyperexcitable ictal activity in paroxysmal phenomena.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/simultaneous-eeg-and-pallidal-local-field-potential-recording-in-the-diagnosis-of-paroxysmal-movements-in-a-patient-with-pde2a-mutation/