Spinal accessory nerve monitoring with clinical outcome measures

Ear, Nose & Throat Journal, August, 2006 by Robert L. Witt, Theresa Gillis, Robert Pratt, Jr.

Abstract

We conducted a prospective study of 11 patients to (1) determine the feasibility of electrophysiologic monitoring of the spinal accessory nerve (SAN) during modified radical neck dissection, (2) determine whether a threshold increase in current is required to stimulate the SAN by comparing the amount of current on initial identification of the SAN and the amount of current after completion of the dissection prior to closure, and (3) determine whether clinical outcome measures of shoulder syndrome at 72 hours and 45 days postoperatively are affected by a threshold increase. We found that 3 of 11 patients (2 7.3%) experienced significant threshold increases (>0.4 mA) on completion of the dissection. Of 8 patients who completed a shoulder syndrome evaluation, 3 (37.5%) had scapular winging, mild to moderate pain, and less than 90% of shoulder abduction. Two of 3 patients with shoulder syndrome had a threshold increase on electrophysiologic monitoring. We conclude that electrophysiologic monitoring of the SAN is feasible. It did not identify a threshold increase in more than 70% of patients. Electrophysiologic integrity of the SAN did not completely correlate with clinical outcome measures for shoulder syndrome.

Introduction

A significant number of articles has been published on electrophysiologic monitoring of (1) the facial nerve during otologic and parotid surgery and (2) the recurrent laryngeal nerve during thyroid and parathyroid surgery. However, information is limited on electrophysiologic monitoring of the spinal accessory nerve (SAN) during modified radical neck dissection.

The major morbidity associated with modified radical neck dissection and selective neck dissection is "shoulder syndrome," which is caused by surgical trauma to the SAN. Shoulder syndrome includes pain, weakness, and deformity of the shoulder-girdle mechanism. Clinical parameters of the shoulder-girdle mechanism that can be measured are shoulder shrug weakness, limitations in shoulder-abduction and/or shoulder-flexion active range of motion, scapular winging at rest, and pain, typically in a characteristic location across the upper border of the trapezius muscle. Trapezius weakness is evidenced by lateral winging, which is differentiated from the medial winging seen in weakness of the serratus anterior muscle.

Objective information on the results of SAN-sparing neck dissections (modified and selective neck dissections) is important because shoulder syndrome secondary to SAN trauma is the most common morbidity of neck dissection. Debate continues regarding the role of neck dissection, particularly following chemoradiation treatment.

We conducted a study to (1) determine the feasibility of electrophysiologic monitoring of the SAN during modified radical neck dissection, (2) determine whether a threshold increase in current is required to stimulate the SAN by comparing the amount of current on initial identification of the SAN and the amount of current after completion of the dissection prior to closure, and (3) determine whether clinical outcome measures of shoulder syndrome are affected by a threshold increase.

Patients and methods

We conducted a prospective study of 11 consecutively presenting patients--aged 39 to 77 years (mean: 62)--who underwent modified (zones 1 through 5 with preservation of the SAN but sacrifice of the sternocleidomastoid muscle and jugular vein) radical neck dissection performed by a single surgeon (R.L.W.) at a single institution. Selective and radical neck dissections were not included in this series.

Electrophysiologic recording of the amount of current on initial identification of the SAN was compared with the amount of current recorded at the completion of the procedure. Clinical correlation measured parameters of shoulder syndrome (shrug, flexion, abduction, winging, and pain) at 72 hours and 45 days. Patients underwent a complete shoulder-girdle evaluation by a physiatrist (T.G.) who specializes in the rehabilitation of head and neck cancer patients.

Patients received no formal physical therapy instruction between the initial and follow-up evaluations. All were instructed to limit their reach to no higher than shoulder height and to avoid carrying more than 5 lbs with the affected arm. Postoperative discharge information included instructions for gentle neck range-of-motion exercises, pectoral stretches performed in a supine or reclined position with the arm abducted less than 90[degrees], and scapular retraction exercises.

Functional evaluations were scheduled to be performed by the physiatrist within the first 72 hours postoperatively and at approximately 45 days postoperatively. The physiatrist was blinded to the results of the electrophysiologic monitoring threshold data.

Pain. The physiatric evaluation included a subjective rating of pain on a scale of 0 (no pain) to 10 (worst pain imaginable). Patients were specifically asked to describe the pain along the superior border of the scapula in the affected shoulder.

Scapular winging. Patients were examined while they were in resting and active scapular positions and during shoulder range-of-motion activities. The presence of scapular winging (i.e., lateral displacement and caudal rotation of the glenoid of the scapula) was assessed with the affected arm at rest and with the patient seated. Scapular winging was rated on a scale of 0 to 3, with 0 indicating no significant displacement or no asymmetry with the contralateral scapula, 1 indicating trace or minimal displacement, 2 indicating moderate displacement, and 3 indicating severe displacement.

Shoulder shrug. Strength in the upper trapezius was assessed by shoulder shrug and rated on a scale of 0 to 5, with 0 indicating no active muscle contraction, 1 indicating trace contraction, 2 indicating weak contraction manifested by an inability to raise the scapula against gravity, 3 indicating contraction sufficient to raise the scapula against gravity only, 4 indicating an ability to raise the scapula against some resistance by the examiner, and 5 indicating an ability to raise the scapula against substantial resistance by the examiner.