Role of Scalene Muscle Block in Selecting Operative Candidates Among Patients with Neurogenic Thoracic Outlet Syndrome

Abstract

Neurogenic thoracic outlet syndrome (nTOS) is a complex clinical entity subject to variable diagnostic regimens. We hypothesized that patients with a positive response, defined as relief of symptoms, following local muscle block of the anterior scalene muscle were more likely to demonstrate benefit following decompression of the thoracic outlet. Patients who underwent surgical decompression for nTOS from 2009 to 2019 at a single institution were identified. Perioperative data were collected to include symptomatology, diagnostic evaluation, intraoperative findings, and postoperative changes in functionality, symptom relief, and recurrence. Groups were then stratified based on the receipt of preoperative local anesthetic block. Univariate analysis was used to assess the impact of demographic and clinical characteristics and response to block on the likelihood of developing persistent or recurrent symptoms and need for reoperation. To explore long-term efficacy, patients were surveyed with regard to symptom relief, symptom recurrence, functionality since surgery, and overall satisfaction with operative outcome. We evaluated 45 patients (49 limbs) who underwent surgical decompression for nTOS between 2009 and 2019; 38.8% (19/49) of these cases were preceded by a scalene muscle block. The patients were predominantly female, 77.8% (35/45) with a mean age of 33.0 ± 11.3 years, and an average age at symptom onset of 25 years. The survey response rate was 68.9% with 31 of 45 patients responding. On postoperative follow up, 91.8% (45/49) of operative limbs were clinically noted to have improvement in function. Survey results demonstrated an average overall preoperative level of functionality of 4.5 ± 2.4 and postoperative level of functionality of 8.1 ± 1.9 (1 = little/no function, 10 = total/high function). NoTably, the population operated on following a positive response to preoperative scalene muscle block reported poorer preoperative functionality of the affected limb than those not screened by this protocol, 2.7 versus 5.4 (P = .0082). Postoperative functionality reported by the two groups was similar, 8.0 versus 8.1 (P = .45). Approximately half of survey respondents reported some degree of symptom recurrence after surgery, with an average time to recurrence of 2 months (range, 1-96 months). There was no difference in symptom recurrence (P = .74) or need for reintervention 4 of 49 cases (P = .80) between block and nonblock groups. Patients operated on following positive response to muscle block reported a lower long-term postoperative pain rating (2.9 vs 3.3), as well as more relief from nTOS symptoms (8.0 vs 7.7), though neither of these differences reached significance. The majority of patients undergoing surgical decompression for relief of nTOS symptoms report improvement in pain and related symptomatology, though some degree of recurrence continues to occur in nearly half of patients. The institution of a preoperative screening protocol involving temporary muscle block selects a patient population with more severe preoperative symptoms. While block protocols may provide another data point to guide patient selection, this study does not demonstrate a statistically significant difference in clinical outcomes in an initial patient group following protocol institution. Further study as additional patients are accrued under the protocol is ongoing.