Abstract Details

Title Epileptic Negative Myoclonus with Lateralized Periodic Discharges: Insights into Pathophysiology

Topic Epilepsy/Clinical Neurophysiology (EEG)

Presentation(s) P7 - Poster Session 7 (11:45 AM-12:45 PM)

Poster/Presentation
Number 1-001

Objective To report two cases of epileptic negative myoclonus (ENM) associated with lateralized periodic discharges (LPDs).

Background Negative myoclonus is a jerky movement characterized by a sudden, brief, and involuntary interruption of sustained muscle activity, known as silent period (SP). ENM is defined by the SP being time-locked to an epileptiform discharge like a spike. ENM has been described in chronic epilepsy syndromes but not in acute neurological conditions with LPDs.

Design/Methods We analyzed the EEG and surface-EMG recordings of two patients with ENM associated with LPDs in the setting of acute pathologies (subdural hematoma and viral encephalitis).

Results

Both patients had contralateral facial clonic seizures on presentation. The facial clonic contractions were time-locked to LPDs with superimposed fast activity (LPD+F) at >2Hz frequency. As the seizures subsided by day five-six, the LPDs became blunt with a reduced frequency of 0.5-1Hz. With sustained muscle contraction, brief type I SPs were noted on sEMG electrodes of the contralateral arm. These SPs were time-locked to the LPDs. The maximum initial negativity of the LPDs localized to the parieto-central region. The LPD-SP latency varied from 20-25ms to 50-60ms.

Conclusions Our results indicate that ENM can occur in acute epileptogenic neurological insults like subdural hematoma and encephalitis with the SPs being time-locked to LPDs. The most likely generator is post-central (S1) as indicated by the localization of the LPDs and SPs being type I only. ENM tends to develop late in the course as the LPDs become less frequent and the superimposed fast activity disappears (“improved epileptogenicity”). Cortical stimulation studies have similarly shown that “low-intensity” stimulation of the peri-rolandic cortex generates inhibition in deeper cortical layers which can interrupt sustained muscle contraction. “High-intensity” stimulation produces high-frequency oscillations which activate the pyramidal tract neurons (descending I-waves), hence producing a positive twitch.

Authors/Disclosures
Neel Fotedar, MD (University Hospitals Cleveland Medical Center) PRESENTER	Dr. Fotedar has received research support from NINDS.
Persen Sukpornchairak, MD (University Hospitals Cleveland Medical Center)	Dr. Sukpornchairak has nothing to disclose.
Joshua Edmondson, MD	Dr. Edmondson has nothing to disclose.

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