Pain-related evoked potentials: a comparative study between electrical stimulation using a concentric planar electrode and laser stimulation using a CO2 laser.

OBJECTIVE: To compare the pain-related evoked potentials (PREPs) obtained by superficial electrical stimulation using a concentric planar electrode to those obtained by CO2 laser stimulation. METHODS: In 12 healthy subjects, PREPs, sympathetic skin reflexes (SSRs), motor reaction times (mRTs), and the conduction velocity (CV) of the recruited nerve fibres were assessed in response to electrical and laser stimulation. RESULTS: In response to superficial electrical stimulation, PREP latencies and mRTs were shorter, while PREP amplitude tended to be increased. By contrast, SSR amplitudes and latencies and estimated CVs of the stimulated nerve fibres did not differ between electrical and laser stimulation. Fifteen minutes after PREP recordings, the residual pain intensity and the degree of unpleasantness were higher for laser stimulation than for electrical stimulation. In addition, CO2 laser stimuli induced dyschromic spots on the skin. For these reasons, all subjects declared that they would prefer superficial electrical stimulation rather than CO2 laser stimulation if they had to perform PREPs again. CONCLUSIONS: The estimated CVs of the recruited nerve fibres and the localized pinprick sensation felt by the subjects suggest that small-diameter fibres in the A-delta range, conveying "first-pain" information, were stimulated in response to superficial electrical stimulation as for laser stimulation. Superficial electrical stimulation using a concentric planar electrode could be a valuable alternative to laser stimulation for assessing PREPs in the practice of clinical neurophysiology.

A reappraisal of the value of lateral spread response monitoring in the treatment of hemifacial spasm by microvascular decompression.

BACKGROUND: Lateral spread response (LSR) to the electrical stimulation of a facial nerve branch is a specific electrophysiological feature of primary hemifacial spasm (HFS). The curative treatment of HFS is based on surgical microvascular decompression (MVD). However, the outcome of this procedure is not always satisfactory. OBJECTIVE: To evaluate the correlation between intraoperative LSR changes and the short- and long-term postoperative clinical outcome following MVD. METHODS: Thirty-two consecutive patients with primary HFS treated by MVD performed with intraoperative LSR monitoring were retrospectively included. The patients were assessed for the presence of HFS and surgical complications at 1 day, 1 month and 6 months after surgery. The long-term clinical result was assessed between 1 and 10 years (mean 5.4 years) using a self-report questionnaire. RESULTS: Patients were divided into three groups based on intraoperative LSR changes: (1) in 15 patients, LSRs were present before incision and disappeared after MVD (47%); (2) in nine patients, LSRs were present before incision but persisted despite MVD (28%); (3) in eight patients, LSRs were absent before surgery and remained so after the procedure (25%). Intraoperative LSR abolition during the MVD procedure correlated with HFS relief in the long term (p<0.0001, Fisher exact test), but not on the first day after surgery (p = 0.3564). CONCLUSIONS: Monitoring MVD by recording LSRs intraoperatively could be of value not only to indicate the resolution of the vasculonervous conflict at the end of surgery, but also to predict a successful clinical outcome in the long term after the surgical intervention.

[Electrophysiological monitoring of cranial motor nerves (V, VII, IX, X, XI, XII)]. / Evaluation électrophysiologique des nerfs crâniens moteurs (V, VII, IX, X, XI, XII).

In various neurosurgical operations, there is a risk of cranial nerve lesion that can be avoided or minimized with intraoperative electrophysiological monitoring. Regarding motor function of the cranial nerves, stimulodetection techniques are used, including electrical stimulation of nerve trunks and electromyographic recording of evoked motor responses. These techniques can be used for monitoring the trigeminal nerve (Vth cranial nerve), facial nerve (VIIth), glossopharyngeal nerve (IXth), pneumogastric nerve (Xth), spinal accessory nerve (XIth), and hypoglossal nerve (XIIth), in particular during surgical removal of tumors of the cerebellopontine angle or skull base. When beginning an operation, electrical stimulation is only used to identify the nerve structures. As removal of the tumor progresses, the goal is to verify that a surgical injury to the nerve is avoided by looking for the absence of any change regarding amplitude, morphology, and latency of motor responses. Intraoperative electromyographic monitoring can also be applied during the surgical treatment of primary hemifacial spasm by microvascular decompression. An effective decompression is usually associated with the disappearance of "lateral spread" motor responses to facial nerve branch stimulation. Therefore, the intraoperative disappearance of the lateral spread responses can be considered a predictive factor of good postoperative clinical outcome, even if this assertion remains a matter of debate.