What is the best study to diagnose thoracic outlet syndrome (TOS)?

Best Diagnostic Study for Thoracic Outlet Syndrome

Catheter venography is the gold standard for diagnosing thoracic outlet syndrome (TOS), particularly venous TOS, as it can demonstrate narrowing of the subclavian vein, venous collateral vessels, and total occlusion that may only be present during stressed positions. 1

Diagnostic Approach by TOS Type

The diagnostic approach varies based on the type of TOS:

Venous TOS (vTOS)

1. Duplex ultrasound - First-line imaging test

   • Evaluates venous thrombosis and patency
   • Can assess cross-sectional area of costocervical space with provocative maneuvers
   • Cost-effective ($200-500) 1
   • Non-invasive initial screening tool

2. Catheter venography - Gold standard

   • Shows narrowing of the subclavian vein
   • Identifies venous collateral vessels
   • Detects total occlusion of the subclavian vein
   • Can reveal findings only present during stressed positions 1

Neurogenic TOS (nTOS)

1. MRI of the brachial plexus

   • High-resolution T1-weighted and T2-weighted sequences
   • Should be performed in both neutral and arms-abducted positions
   • Necessary for accurate diagnosis 1
   • Costs approximately $1000-2000 1

2. Electrodiagnostic studies

   • Medial antebrachial cutaneous (MABC) sensory nerve action potential testing is particularly valuable
   • Has shown abnormal results in all tested patients with true neurogenic TOS 2
   • Should be included as a screening method 2

Arterial TOS

1. Systolic blood pressure measurement

   • A difference of more than 25 mmHg between arms is considered significant
   • Indicates potential arterial compression 1

2. Chest radiography

   • Identifies osseous abnormalities (cervical ribs, first rib anomalies)
   • Relatively inexpensive ($50-200) 1
   • Should be included in initial workup

Diagnostic Algorithm

1. Initial screening:

   • Chest radiography to identify bony abnormalities
   • Duplex ultrasound with provocative maneuvers
   • Blood pressure measurement in both arms

2. Advanced imaging based on suspected TOS type:

   • Venous TOS: Proceed to catheter venography
   • Neurogenic TOS: MRI of brachial plexus + electrodiagnostic studies
   • Arterial TOS: CTA or catheter angiography

Important Clinical Considerations

• TOS is not a diagnosis of exclusion; there should be evidence of a physical anomaly that can be corrected 3
• Clinical testing alone has poor accuracy 1, with sensitivity and specificity issues 4
• Delayed diagnosis beyond 14 days can significantly worsen outcomes 1
• The estimated prevalence of symptomatic TOS is only 10 per 100,000 people 1, making it a relatively rare condition

Pitfalls to Avoid

• Relying solely on clinical examination for diagnosis, as it has poor accuracy 1, 4
• Failing to perform imaging in both neutral and stressed positions, as some findings may only be present during provocative maneuvers 1
• Neglecting to consider MABC nerve conduction studies, which have shown high sensitivity in true neurogenic TOS 2
• Overlooking the need for advanced imaging (MRI) in cases of suspected neurogenic TOS 1

While multiple diagnostic modalities are available, catheter venography remains the gold standard for definitive diagnosis of TOS, particularly venous TOS, with MRI being essential for neurogenic TOS and appropriate electrodiagnostic studies serving as valuable adjuncts to imaging.