What is the best injection technique for diagnosing neurogenic thoracic outlet syndrome?

Best Injection Technique for Diagnosing Neurogenic Thoracic Outlet Syndrome

Ultrasound-guided anterior scalene muscle injection with local anesthetic is the best diagnostic injection technique for neurogenic thoracic outlet syndrome (nTOS), as it confirms the diagnosis if symptoms are relieved following injection. 1, 2

Diagnostic Algorithm for nTOS

Step 1: Initial Imaging

• Begin with chest radiography to identify osseous abnormalities such as cervical ribs, first rib anomalies, and congenital malformations 3
• MRI of the chest is superior for evaluating nTOS due to its ability to delineate the brachial plexus and cervical spine 3

Step 2: Confirmatory Diagnostic Injection

• Ultrasound-guided injection technique:
  • Position patient supine with head turned away from the affected side
  • Use ultrasound to identify the anterior scalene muscle
  • Inject local anesthetic (typically 5-10 mL of 1% lidocaine) into the anterior scalene muscle
  • Positive diagnostic test: Significant relief of symptoms within minutes of injection 1, 2

Step 3: Additional Diagnostic Considerations

• If diagnostic uncertainty remains, consider:
  • Botulinum toxin injection into the anterior scalene muscle for longer-lasting diagnostic and potentially therapeutic effect 2
  • Ultrasound-guided pectoralis minor injection if retropectoralis minor space compression is suspected 2

Evidence Quality and Considerations

The American College of Radiology guidelines strongly support the use of ultrasound-guided anterior scalene muscle injection as a diagnostic tool for nTOS 3, 1. This technique has several advantages:

• Provides real-time visualization of the injection target
• Allows direct assessment of the anatomical site of compression
• Offers immediate feedback on symptom relief
• Helps predict potential response to surgical intervention 2

Common Pitfalls and How to Avoid Them

• False negatives: Ensure proper needle placement with ultrasound guidance to avoid inadequate anesthetic delivery
• Incomplete assessment: Remember that nTOS may involve multiple compression sites; consider additional injections if initial response is partial 2
• Misdiagnosis: Do not rely solely on injection response; correlate with clinical presentation and imaging findings 3
• Technical challenges: The anterior scalene is in close proximity to important neurovascular structures; ultrasound guidance is essential to avoid complications 1

Alternative Approaches

While anterior scalene muscle injection is the gold standard, other diagnostic approaches include:

• Pectoralis minor injection for cases with predominant retropectoralis minor space compression 2
• Combined injections for patients with multiple compression sites 2
• Botulinum toxin injection for both diagnostic and therapeutic purposes in selected cases 4

The diagnostic injection not only confirms nTOS but also helps predict the likelihood of success with surgical intervention, making it an essential component of the diagnostic algorithm 2, 5.