Abstracts

Vagal Nerve Stimulation (VNS) is 6 years post FDA approval & enjoys acceptance as an important tool to manage medically resistant epilepsy. Enough experience exists to define the role VNS fills in comprehensive epilepsy managment.
Our epilepsy surgery experience over 6 yrs (5 yrs from FDA approval, w [gt]1 year follow up) was reviewed to understand how VNS has evolved & influenced contemporary treatment modalities. All data is prospective except long term post op data that was retrospectively collected. All underwent excepted epilepsy pre-surgical work up.
1221 consecutive epilepsy procedures, contained 296 (24%)VNS ops for 248 unique patients. Ave age VNS group = 27.1 yrs, & 145 were female. 28 patients had 1, 24 had 2, 4 had 3, & 12 had 5 or more non-VNS procedures in addition to VNS. Follow up exists for about 75% of entire series, all w [gt] 1 yr. 248 are 1st implants & 48 revisions. Revisions included 35 battery replacements & 23 removals for complications or other adversities. Complications & relative risks will be discussed. Data summary : 296/1221 (24%) of all epilepsy surgery during review period; 35/296 (12%) revisions; & 23/296 (8%) removals. Most VNS cases determined from non-inv workup : 246/296 (83%). VNS prior to therapeutic crani : 36/296 (12%). Inv proc (monitoring or therapeutic crani) followed by VNS : 12/296 (4%). Inv monitoring preceding VNS, & then followed by another therapeutic crani in 2/296 ([lt]1%). Efficacy reported using modified Engel score that assigns preop scores defined by last 2 med changes or last 1/2 yr of med therapy as the therapeutic [quot]function[quot] considered equivalent to surgery in post op score. 192/248 (77%) (48 rev or rem) had outcome available for anaylsis. Ave score pre & post implant = 3.9 (s.d. = 0.4) & 2.9 (s.d. = 0.8) respectively. Pre & post VNS score of 1/2/3/4 were 0.7/1.3/6/92% & 7/12/58/23% respectively. 50% reduced Sz freq occurred in 57%, 75% reduced in 45%, & 90% reduced in 31%. Most common morbidity is infection 1.7% & vagal nerve injury 1.7% (0.8% transient.) Comparing results to cranial surgery: 1-stage resections (primarily ant med temp lobectomy w hippocampectomy) stratified by Engel scores 1/2/3/4 respectively = 91/6/4/0% , w 76% follow up. 2-stage procedures, involving inv VEEG prior to resection, had respective outcome scores 64/14/14/8% w 81% follow up. 3-stage group had outcome of 50/19/28/3% w 76% follow up.
The comprehensive workup, involving VEEG, is recommended. Our view is that when excellent Sz control w craniotomy is possible then invasive surgical modality over VNS should be offered. Of patients selected for invasive procedures only 4.1% went on to VNS. The assumption being that VNS was appropriately selected as a management modality when a comprehensive evaluation is performed. W/out a typical workup neither VNS or invasive therapeutic procedures can be adequately prescribed. VNS appears to be filling a specific niche in the management landscape.