Diagnostic Accuracy of Scalene and Pectoralis Minor Muscle Blocks for Thoracic Outlet Syndrome: A Systematic Review and Meta-Analysis

Abstract

Background

Thoracic outlet syndrome (TOS) is a complex neurovascular condition that remains challenging to diagnose, particularly neurogenic TOS (nTOS), which comprises most cases. While vascular TOS has clear diagnostic criteria, nTOS diagnosis relies on clinical assessments, imaging, and electrophysiologic studies. Scalene and pectoralis minor muscle blocks have been proposed as diagnostic tools, but their accuracy remains uncertain.

Objective

This systematic review and meta-analysis assesses the pooled sensitivity, specificity, and diagnostic accuracy of scalene and pectoralis minor blocks for TOS.

Methods

A systematic literature search was performed across PubMed, Embase, Scopus, Cochrane Library, Web of Science, and Google Scholar following PRISMA guidelines. Studies evaluating the diagnostic accuracy of these blocks for TOS were included. The QUADAS-2 and Newcastle-Ottawa Scale were used for quality assessment. A meta-analysis using RevMan and STATA assessed pooled sensitivity, specificity, and diagnostic odds ratios (DORs).

Results

Of the 180 reports yielded by the search, 12 studies met inclusion criteria (950 patients). Pooled sensitivity for scalene and pectoralis minor blocks was 87% (95% CI: 83%-90%), while specificity was 34% (95% CI: 26%-43%). The diagnostic odds ratio was 3.98 (95% CI: 2.50-6.34). Substantial heterogeneity was observed (I² = 68%, P < 0.001), attributed to variations in injection protocols, outcome definitions, and patient selection.

Conclusion

Scalene and pectoralis minor blocks have high sensitivity but low specificity for TOS diagnosis. Their use as stand-alone diagnostic tools is limited. However, they may be valuable within a multimodal diagnostic framework integrating clinical evaluation, imaging, and electrophysiologic testing.