Abstracts

RATIONALE: Vagus nerve stimulation (VNS) is a widely used procedure for the treatment of medication-resistant epilepsy. During VNS, collateral spread of the applied current is practically inevitable, with the potential of stimulating other neural structures in the vicinity of the vagus nerve. Since the currents applied during VNS are very small, the probability of collateral stimulation appears to be low. However, we found several patients that were reporting very specific signs and symptoms that could be best explained by this phenomenon. We reviewed our experience with collateral stimulation during VNS therapy.
METHODS: The medical records from 78 patients on VNS for the treatment of epilepsy were reviewed looking for signs or symptoms consistent with collateral stimulation of adjacent nerves. These symptoms had to occur exclusively during [dsquote]ON[dsquote] periods of stimulation. A detailed description was obtained and, whenever possible, the patients were examined while experiencing the symptoms. A neuroanatomical correlation of the symptoms was attempted based purely on the clinical findings. No neurophysiologic techniques were used in this study.
RESULTS: Eight patients were found to have signs or symptoms consistent with collateral stimulation. Clinical manifestations (probable nerve/muscle involved) were as follows: twitching or spasm of muscles in the left supraclavicular region (ansa cervicalis/infrahyoid muscles, or ventral rami of spinal nerves/longus colli, longus capitis, scaleni): 5 cases; left upper abdominal twitching, jerky respiration (phrenic/hemidiaphragm): 3 cases; left shoulder twitching, abduction (upper trunk of brachial plexus or suprascapular/deltoid or supraspinatus): 1 case; left upper extremity tingling (upper trunk of brachial plexus): 1 case. Range of VNS settings at the time of the symptoms was 1-2.25 mA, 30 Hz and 250-500 [mu]sec.
Symptoms were present during every [dsquote]ON[dsquote] period in only 1 patient. They were triggered by a certain posture (head turning to left or left lateral decubitus) in 5 patients. Symptoms were relieved by a change in head/neck position in 4 patients. Reduction of the output current resolved the symptoms in 2 patients, the rest did not require any specific intervention.
CONCLUSIONS: Symptoms attributable to collateral activation of adjacent neural structures are relatively common during VNS. The two most common presentations were activation of muscles in the left supraclavicular region and the left hemidiaphragm. Symptoms were mild or moderate and rapidly resolved when the output current was reduced. In most patients, symptoms were only observed when the stimulation occurred while in a certain head, neck or body posture. Most patients did not require any specific adjustment of the VNS settings and were able to control the problem by avoiding those specific postures. A spontaneous, gradual improvement with time was seen in most patients.
(Disclosure: Honoraria - Cyberonics)