Abstracts

Rationale: Atonic seizures are typically known to occur in generalized epilepsies. Over the last decade, focal seizures have been increasingly recognized to exhibit a similar clinical presentation, particularly when originating from the frontal lobe. Interestingly, the Primary negative motor area (PNMA), the supplementary negative motor area (SNMA), and the primary somatosensory cortex are postulated regions implicated in the pathophysiology and clinical presentation of atonic seizures.

Methods: Our objective is to describe the case of a patient with medically refractory epilepsy (MRE), who underwent Phase II stereotactic electroencephalogram (sEEG) monitoring and was found to have right focal onset seizures with ictal atonia.

Results: A 39-year-old-man right-handed man with MRE and a prior right frontal subpial transection at 10 years old presented to our outpatient Neurology clinic for evaluation of “drop attacks” with loss of awareness and no aura. On video EEG, he was found to have rhythmic sharp and slow waves with onset over right frontocentral area. Clinically, the patient exhibited an initial head drop with subtle left head version, followed by bilateral hand dystonic posturing, then followed by brief right sided myoclonic movement of his arm and leg. Each event was stereotyped, lasted ten seconds, and occurred multiple times a day.  He completed Phase I Epilepsy Surgery evaluation. Brain MRI showed changes from prior surgery and Focal Cortical Dysplasia Type II at the junction of right precentral and superior frontal gyri.  Neuropsychological evaluation and PET Scan were non-lateralizing. He underwent Phase II evaluation with implantation of 126 sEEG electrodes over the bilateral frontal superior and middle frontal gyri.  Seizure onset zone on sEEG was identified by temporal and spatial evolution over right medial motor (RMM) and hand motor (RMH) regions. There was onset of fast rhythmic activities at alpha frequencies, followed evolution into rhythmic theta activities and then by diffuse slowing over the RMM and RMH. Interestingly, three seconds after EEG onset, increased frequencies are observed over the right sensory hand (RSH) and posterior right middle frontal gyrus (RMFP), followed by ictal atonia. Due to the eloquent location of the seizure onset zone, the patient will be pursuing treatment with Responsive Neurostimulation.

Conclusions: This is an interesting case highlighting a seizure with focal onset and multiple motor manifestations. Predominant atonia which evolved later into subtle tonic and myoclonic movements involving the bilateral upper extremities. Clinicians should have a high index of suspicion for ictal atonia when the suspected onset zone is near or around the PNMA, SNMA or primary sensory cortex. Epilepsy surgery evaluation requires meticulous planning and collaboration. Further studies are needed to determine the cortical networks and incidence of ictal atonia. Although we did not study this, we suspect that ictal atonia is an under-recognized phenomenon among neurologists.

Funding: No funding to disclose