Abstracts

Rationale: The literature for Deep Brain Stimulation (DBS) for Parkinson’s disease contains numerous case reports and a case series that describe a rare phenomenon of transient lesional symptoms due to inflammation surrounding the DBS electrodes in the post-operative period. These patients experienced headaches, diplopia, word-finding difficulties, gait difficulties, and encephalopathy 4-8 days post-operatively. Responsive Neuro-Stimulation (RNS) implantation is a relatively new treatment for patients with medically-refractory focal epilepsy and this phenomenon has not yet been reported for RNS.  We share the first probable case of RNS electrode-induced peri-operative inflammatory reaction that resulted in a transient constellation of neurological signs and symptoms, including seizure freedom and inability to make new memories. Methods: Case report and literature review. Results: A 36 year old right-handed man with severe medically-refractory bilateral mesial temporal lobe epilepsy underwent an uncomplicated implantation of RNS with bilateral hippocampal depth leads and was discharged home in excellent condition on stable medications. 12 days postoperatively, he presented with new onset diplopia, encephalopathy, ataxia, tremor, apraxia, short-term memory impairment, and visual hallucinations. Anticonvulsant levels were within therapeutic ranges. Infectious and metabolic work-up was unremarkable. Head CT demonstrated new hypodensities in the bilateral occipital lobes concerning for new edema vs artifact. The patient was treated with high-dose steroids with complete resolution of presenting symptoms within one week of presentation. CT at the time of discharge showed marginal improvement of presenting CT changes. MRI was not performed because it is not yet FDA-approved for RNS. During the week-long symptomatic period, the patient reported no seizures and there was a dramatic reduction in RNS detections of epileptiform activity to nearly-zero (from an average of 40+ per day).  After discharge, seizure burden increased back to baseline without return of the symptoms prompting his postoperative admission. Conclusions: To date, there have been no published reports of lead-related edema or inflammation in the peri-operative period related to RNS placement. Lead edema and inflammation related to DBS implantation has been sporadically described in the movement disorder literature and also has been rarely described in the intracranial electrocorticography literature, although the pathophysiological mechanisms are not well understood. Animal models indicate that electrode implantation causes structural immunologic changes which likely have an effect on neuron function. Acute astrocytic reaction is followed by gliosis which surrounds the electrodes, ultimately causing alterations in electrical impedance. Neurostimulation causes both acute and long term changes in neuron behavior and neural network modulation through GABA-mediated mechanisms, neurotrophic factor upregulation, and gene expression. It is unclear in the case patient how the electrode related cortical inflammatory reaction disrupted these mechanisms and led to the temporary decrease in seizure burden. Funding: No funding was received in support of this abstract.