Insufficient efficacy of vagus nerve stimulation for epileptic spasms and tonic spasms in children with refractory epilepsy.

BACKGROUND: Vagus nerve stimulation (VNS) leads to palliation of refractory seizures. Epileptic spasms (ES) and tonic spasms (TS) appear in children with West syndrome and symptomatic generalized epilepsy. Both types of spasms are often characterized by truncal muscular contractions and ictal electroencephalography (EEG) findings comprising the contiguous phases: phase 1) 15-20 Hz, spindle-like fast activity (occur in 70%), 2) diffuse polyphasic δ/θ waves (100%), and 3) electrodecremental activity (70%). Here, we examined the effect of VNS on these spasms that are uniformly associated with the EEG and electromyogram changes.

METHODS: A consecutive series of 32 patients satisfied the inclusion criteria consisting of 1) medically refractory epilepsy, 2) VNS implantation between 2010 and 2015, 3) implantation of VNS before the age of 20 years, and 4) follow-up >2 years. From this cohort, 16 patients had spasms (ES/TS group), whereas the remaining 16 had partial seizures with or without secondary generalization (PS/SG group). We compared seizure outcomes between the two groups, and also determined the factors predicting these outcomes within the ES/TS group.

RESULTS: The outcomes after 2 years of implantation, defined using the McHugh classification, were as follows: II (for 2 patients), III (5), and V (9) in the ES/TS group; and I (3 patients), II (6), III (2), IV (1), and V (4) in the PS/SG group. The ES/TS group had significantly worse outcomes than the PS/SG group (p = 0.024, Mann-Whitney U test). Multivariate ordinal logistic regression analysis revealed that shorter mean durations of ictal events were associated with better seizure outcomes following VNS implantation (p = 0.007).

SIGNIFICANCE: Only 13% of the patients in the ES/TS group had seizure reductions of greater than 50%. VNS was less effective for the treatment of patients with ES/TS than for those with PS/SG and those described in previous studies.