A study indicates that seizure control improves in patients with epilepsy when vagus nerve stimulation (VNS) increases blood flow in the thalamic areas of the brain.
VNS causes activation of synaptic activities at multiple sites in the brainstem and both cerebral hemispheres. The results of the study confirm earlier evidence that showed that altered thalamic processing contributes to the anti-seizure effects of VNS.
"The study results are significant because they show that if patients respond to VNS therapy in the short-term they will continue to respond favorably over the long-term," said Thomas R. Henry, Neurology, Emory University. "In addition, these results also suggest that if patients undergoing VNS therapy show bilateral thalamic activation in the short-term, we can accurately predict long-term seizure control-something that has not been possible up until now."
The study involved 11 patients with partial epilepsy who were uncontrolled with AEDs and who had complex partial and general tonic clonic seizures. During one year of VNS, seizure control improved in most patients compared to baseline seizure rates, with a reduction of up to 91 per cent.
Each patient had brain flow imaging with positron emission tomography after three months of VNS. Imaging compared VNS-on versus VNS-off states and showed numerous sites of brain activity with VNS on. Among those sites, only the right and left thalami (which may manage excitability of the cortex in the people with epilepsy) were significantly associated with greater seizure reduction.
"Our study shows that VNS may benefit other blood functions," stated Henry. "Blood flow activations in frontal cortex and subcortical sites may alter attention, memory and mood. These activations may not serve to control seizures but might benefit depression and memory impairment."
VNS stimulates the limbic region of the brain that is responsible for mood, motivation, sleep, appetite, alertness and seizures. A stopwatch-sized generator - the Neurocybernetic Prosthesis (NCP) System - implanted just under the skin in the left chest area delivers pre-programmed, mild, intermittent electrical pulses to the left vagus nerve, 24 hours a day.
VNS with the Cyberonics NCP System was approved in 1997 for use as an adjunctive therapy in reducing the frequency of seizures in adults and adolescents over 12 years of age with medically refractory partial onset seizures. In addition, the NCP System is currently approved for epilepsy in all the member countries of the European Union, Canada, Australia and other markets. VNS with the Cyberonics NCP System was also recently approved for sale in the European Union and in Canada as a treatment of depression in patients with treatment-resistant or treatment-intolerant major depressive episodes including unipolar depression and bipolar disorder (manic depression).