Abstracts

Few studies provide data about experience with modifying antiepileptic drug (AED) regimens in patients treated with vagus nerve stimulation (VNS). Since most patients continue to have seizures to some extent after VNS, it is helpful to know if AED changes, in particular reduction of medication, is a realistic goal. We present data on clinical experience of AED regimens in patients prior to VNS implant and after 4 years of treatment with VNS. 42 patients underwent VNS implant for medically intractable seizures at the University of Michigan between January, 1999, and May, 2001. Patients with consistent follow up for 4 years post implant were included in this retrospective analysis. 9 patients were excluded for inadequate follow up due to: VNS turned off (2), lost to follow up (4), VNS explanted due to discomfort (1), and death (2). The 33 patients ranged in age from 15 to 57 at implant. 13% were female. 23 (70%) had focal epilepsy (FE), 2 (6%) had primary generalized epilepsy (PGE), and 8 (24%) had symptomatic generalized epilepsy (SGE). Mean number of AED[apos]s pre VNS implant was 2.2, range 1-4 (FE), 2.5, range 2-3, (PGE), 2.5, range 1-4 (SGE), and at 4 years after VNS was 2.6, range 0-5, (FE), 3.5, range 3-4, (PGE), 3.2, range 2-5, (SGE). At 4 years of VNS treatment, 11 patients had added one AED, 6 patients had added 2 AEDs, and 3 patients had reduced one AED, compared to number of AED[apos]s pre-implant. One patient discontinued AED[apos]s without medical advice. 3 patients with [gt]75% decrease in seizure frequency were offered AED reduction and declined. 9 patients changed AED[apos]s during the 4 years but total number of AED[apos]s remained the same (except for cross-over intervals). At 4 years of VNS, compared to pre-implant, 6 patients had 25% decrease in seizure frequency 4(FE), 2(SGE). 10 patients had 50% decrease in seizure frequency, 8(FE), 2(SGE) and 7 patients had 75% decrease in seizure frequency 5(FE), 1(PGE), 1(SGE). 2 patients were seizure free 1(FE), 1(PGE) and 8 experienced no change in seizure frequency 5(FE) 3(SGE). In the majority of patients in this series, AED[apos]s stayed the same, or increased at 4 years after treatment with VNS, as compared to pre implant, even though seizures were reduced with VNS, overall. Decrease in seizure frequency at 4 years after VNS related more to benefit noted from VNS, as increasing numbers of AED[apos]s did little to improve seizure control in most patients. Few patients were able to reduce AED[apos]s, or were reluctant to do so. This information can be important in counseling patients about expectations for continuation of AED[apos]s after treatment with VNS. These results also reflect the extremely refractory nature of epilepsy in patients treated with VNS.