Responsive Neurostimulation System
Patients with medically refractory temporal lobe epilepsy (TLE) are candidates for neuromodulation procedures. While vagus nerve stimulation (VNS) was historically the procedure of choice for this condition, the responsive neurostimulation system (RNS) has come into favor for its more targeted approach.
This treatment was approved by the U.S. Food and Drug Administration (FDA) in 2013.
Neuromodulation such as vagus nerve stimulation (VNS) and responsive neurostimulation (RNS) are safe and effective strategies for medically intractable epilepsy secondary to complex partial seizures, but researchers have yet to compare their efficacies.
Wang et al. retrospectively reviewed the records of all patients with TLE who underwent VNS or RNS placement at our institution from 2003 to 2018. The primary outcome was change in seizure frequency. Other outcomes included Engel score, change in anti-epileptic medications, and complications.
Twenty-three patients met inclusion criteria; 11 underwent VNS and 12 underwent RNS. At baseline, the 2 groups were statistically similar regarding age at surgery, epilepsy duration, and preoperative seizure frequency. At last follow-up, both groups displayed reduced seizure frequency (mean reduction of 46.3% for the VNS group and 58.1% for the RNS group, p = 0.49). Responder rate, Engel score, and change in medications were statistically similar between groups. Compared to 0.0% of the VNS group, 13.3% of the RNS group experienced infection requiring re-operation.
Despite their different mechanisms, VNS and RNS resulted in similar response rates for patients with TLE. We suggest that VNS should not be excluded as a treatment for patients with medically refractory TLE who are not candidates for resective or ablative procedures 1).
The goal of a study of Ellens et al. was to compare VNS and RNS efficacy at reducing seizure frequency and complication rates in subjects with medically intractable epilepsy secondary to complex partial seizures.
This is a retrospective chart review of 30 patients with medically intractable complex partial epilepsy, who underwent either VNS or RNS placement at a single institution between June 2012 and January 2016. There was a mean follow-up of 19 months. Seizure frequency reduction and complications were identified.
The median seizure frequency reduction was similar for VNS (66%) and RNS (58%). There was no major morbidity or mortality, and the frequency of minor complications was similar between VNS (15%) and RNS (18%).
They found that VNS and RNS reduced the median seizure frequency similarly with no difference in morbidity or mortality. Further prospective studies are warranted as VNS and RNS therapy improves over time 2).
Boon et al., conducted a systematic review on the currently available neurostimulation modalities primarily with regard to effectiveness and safety.
For vagus nerve stimulation (VNS), there is moderate-quality evidence for its effectiveness in adults with drug-resistant partial epilepsies. Moderate-to-low-quality evidence supports the efficacy and safety of deep brain stimulation (DBS) and responsive neurostimulation (RNS) in patients with DRE. There is moderate-to-very low-quality evidence that transcranial direct current stimulation (tDCS) is effective or well tolerated. For transcutaneous vagus nerve stimulation (tVNS), transcranial magnetic stimulation (TMS) and trigeminal nerve stimulation (TNS), there are insufficient data to support the efficacy of any of these modalities for DRE. These treatment modalities, nevertheless, appear well tolerated, with no severe adverse events reported.
Head-to-head comparison of treatment modalities such as VNS, DBS and RNS across different epileptic syndromes are required to decide which treatment modality is the most effective for a given patient scenario. Such studies are challenging and it is unlikely that data will be available in the near future. Additional data collection on potentially promising noninvasive neurostimulation modalities like tVNS, TMS, TNS and tDCS is warranted to get a more precise estimate of their therapeutic benefit and long-term safety 3).
Jobst BC, Kapur R, Barkley GL, Bazil CW, Berg MJ, Bergey GK, Boggs JG, Cash SS, Cole AJ, Duchowny MS, Duckrow RB, Edwards JC, Eisenschenk S, Fessler AJ, Fountain NB, Geller EB, Goldman AM, Goodman RR, Gross RE, Gwinn RP, Heck C, Herekar AA, Hirsch LJ, King-Stephens D, Labar DR, Marsh WR, Meador KJ, Miller I, Mizrahi EM, Murro AM, Nair DR, Noe KH, Olejniczak PW, Park YD, Rutecki P, Salanova V, Sheth RD, Skidmore C, Smith MC, Spencer DC, Srinivasan S, Tatum W, Van Ness P, Vossler DG, Wharen RE Jr, Worrell GA, Yoshor D, Zimmerman RS, Skarpaas TL, Morrell MJ. Brain-responsive neurostimulation in patients with medically intractable seizures arising from eloquent and other neocortical areas. Epilepsia. 2017 Jun;58(6):1005-1014. doi: 10.1111/epi.13739. Epub 2017 Apr 7. PubMed PMID: 28387951.