Abstracts

Rationale: Patients implanted with vagal nerve stimulator (VNS) have had about 50% reduction in frequency of seizures in approximately 3 years of implantation. End of battery life (EOBL) is defined when generator no longer delivers any output which denotes needing replacement and this is preceded by end of effective stimulation (EOES) which can be defined as period of days to months during which patients may feel irregular stimulation, no stimulations or loss of VNS induced side effects with impairment in seizure control. Replacement of VNS should be considered when approaching EOES and delay in replacement should be prevented as it can cause permanent loss of control in seizure control. We present 2 cases with seizure exacerbation prior to battery depletion in whom seizure control was achieved by early VNS replacement.

Methods: A retrospective chart review was performed of 2 patients who had seizure exacerbation prior to the expected EOES date.

Results: Case 1: 63-year-old male with history of medically refractory multifocal epilepsy with onset shortly after birth. His seizures failed to respond to more than 10 antiepileptic drugs (AEDs) over years. Subsequently, he had VNS placement in 2014 with decrease in seizure frequency and had battery replacement in 2018. In 8/2020, he presented with seizure exacerbation and upon VNS interrogation, his generator was noted to have low battery life at 11-25%. He underwent battery replacement in 10/2020. Over the next few weeks, he had approximately 50% decrease in clinical seizure frequency.

Case 2: 25-year-old male with history of intellectual impairment, Lennox Gastaut Syndrome, cerebral palsy, hydrocephalus with ventriculoperitoneal shunt. His seizure onset was at age of 2 months, has had multiple seizure types including generalized tonic clonic, atonic, atypical absence and myoclonic seizures; failed multiple AEDs and his medication regimen optimized with 6 AEDs without complete seizure control. He had VNS placement in 2002 with improvement in seizure control and had battery replacement in 2017. In 3/2021 he presented with increase in seizure frequency and prolongation of seizures. His shunt was determined to be working well but VNS battery was low at 11-25%. His VNS was replaced without any change in medications. Shortly after the VNS replacement, he had an improvement in seizure frequency returning back to his prior established baseline frequency.

Conclusions: Our report suggests that some patients are more sensitive to VNS battery depletion and may present with worsening in seizure control before the expected EOES date. There are no specific guidelines regarding when the VNS generator battery should be replaced; however, prompt recognition of EOES is essential since delay in replacement can cause permanent loss of seizure control. Future studies may be useful in predicting who are more susceptible for worsening in seizure control and may be a candidate for battery replacement before any sign of EOES.

Funding: Please list any funding that was received in support of this abstract.: N/A.