Intraoperative electrophysiological monitoring for C1-2 spinal cord stimulation

Abstract

OBJECTIVE This study is a retrospective case series involving C1-2 spinal cord stimulation in patients with complex regional pain syndrome (CRPS) under general endotracheal anesthesia. Currently, C1-2 paddle lead placement is an accepted practice, which provides effective cervical stimulation to ameliorate upper-extremity and sometimes lower-extremity symptoms experienced by patients with CRPS. However, this technique must be performed under general endotracheal anesthesia rather than in an awake or semiconscious state due to intraoperative safety concerns and patient comfort. The authors aim to provide additional data to support the following novel technique: the use of somatosensory evoked potential (SSEP) diminution data to assist with proper midline placement of C1-2 leads under general anesthesia. METHODS SSEP median nerve (MN) and posterior tibial nerve (PTN) data were collected from 6 patients undergoing placement of C1-2 leads under general anesthesia. Fluoroscopy was used as an initial guide for proper anatomical midline placement. This was followed by the activation of the spinal cord stimulator and simultaneous collection of primarily MN SSEPs as well as PTN SSEPs for physiological midline placement. Unilateral and bilateral reductions in SSEPs assisted with the correct lateralization of the lead to ensure effective postoperative coverage according to the patient's individual preoperative symptoms. RESULTS Six patients were monitored using SSEPs and repeatable, reliable MN and PTN baseline responses were obtained from all. A reduction in amplitude ranging from 5% to 87% was observed, confirming inhibition of dorsal column conduction, and an average pain relief of 63% at short-term and 64% at long-term follow-up was recorded with 6 of 6 and 5 of 6 patients responding, respectively. CONCLUSIONS Intraoperative SSEP collision study testing appears to be a safe technique to monitor placement of C1-2 paddle leads intraoperatively under general anesthesia.

Keywords: C-1; C-2; CRPS = complex regional pain syndrome; EMG = electromyography; GABA = γ-aminobutyric acid; LE = lower extremity; MN = median nerve; PTN = posterior tibial nerve; SCS = spinal cord stimulation; SSEP = somatosensory evoked potential; TO4 = train of four; UE = upper extremity; cervical; complex regional pain syndrome; paddle lead; somatosensory evoked potential; stimulation.