Vagus nerve stimulation in refractory epilepsy: SPECT activation study.

Area of Science:

• Neuroscience
• Neurology
• Medical Imaging

Background:

• Refractory epilepsy affects numerous patients, with left-sided vagus nerve stimulation (VNS) offering a viable treatment option.
• The precise mechanism by which VNS alleviates seizures remains incompletely understood.
• Investigating acute VNS effects is crucial for understanding its therapeutic action in epilepsy.

Purpose of the Study:

• To investigate the acute effects of initial VNS on cerebral blood flow in patients with refractory epilepsy.
• To elucidate the neurophysiological mechanisms underlying VNS efficacy using SPECT imaging.
• To correlate VNS-induced brain activity changes with seizure reduction.

Main Methods:

• A perfusion activation study using SPECT was conducted on twelve patients with refractory complex partial seizures (CPS) +/- secondary generalization (SG).
• Regional cerebral blood flow (rCBF) was assessed using a (99m)Tc-ethyl cysteinate dimer activation study before and immediately after initial VNS.
• Semiquantitative analysis and voxel-by-voxel analysis (statistical parametric mapping) were employed to analyze SPECT images.

Main Results:

• VNS demonstrated a range of seizure frequency changes, from 100% decrease to 0%.
• A consistent decrease in activity was observed in the left thalamus (ratio stimulator on/off = 0.94 +/- 0.04; P = 0.005).
• SPECT analysis revealed significant deactivation in the left thalamus, extending to the ipsilateral hippocampus, with no correlation to seizure reduction.

Conclusions:

• Acute VNS may reduce seizure onset or propagation by inhibiting the thalamic relay center.
• SPECT imaging is a valuable tool for studying the cerebral physiopathologic effects of VNS in epilepsy.
• Further research is needed to reconcile findings with PET data and explore temporal effects of VNS-induced hemodynamic responses.