Can thoracic outlet syndrome (TOS) cause syncope?

Can Thoracic Outlet Syndrome Cause Syncope?

Yes, thoracic outlet syndrome (TOS) can cause syncope, particularly in cases of vascular TOS where subclavian artery compression leads to impaired cerebral blood flow, especially during upper extremity movement or exercise.

Mechanisms of Syncope in TOS

Syncope related to TOS can occur through several mechanisms:

1. Vascular Mechanisms:

   • Subclavian steal syndrome - retrograde flow in the vertebral artery causing diminished cerebral blood flow 1
   • Arterial compression during arm movement leading to cerebral hypoperfusion 2
   • Impaired cerebral blood flow during provocative positioning 1

2. Neurologic Mechanisms:

   • Vasovagal response triggered by pain or compression of neural structures 1
   • Baroreceptor activation in the aortic arch or carotid sinus 1

3. Cardiac Mechanisms (less common):

   • Arrhythmias triggered by autonomic nervous system dysfunction 1

Diagnostic Approach for TOS-Related Syncope

Key Clinical Findings

• Positional Triggers: Syncope occurring during upper extremity exercise or specific arm positions 1
• Associated Symptoms: Upper extremity pain, numbness, tingling, weakness, swelling, discoloration 2
• Blood Pressure Differences: A systolic blood pressure difference >25 mmHg between arms is significant 2
• Provocative Maneuvers: Symptoms reproduced with arm abduction or overhead positioning 2

Diagnostic Testing

• Duplex Ultrasound: Evaluates vascular compression with provocative maneuvers 2
• MRI with Dynamic Positioning: Essential for visualizing compression that may only be evident during arm abduction 2
• MR Angiography/Venography: Assesses subclavian vessel compression in neutral and abducted positions 2
• Chest Radiography: Identifies osseous abnormalities like cervical ribs 2

Management of TOS-Related Syncope

Conservative Management (First-Line)

• Physical Therapy: Targeted exercises to strengthen supporting muscles 2
• Postural Correction: Addressing contributing factors 2
• Activity Modification: Avoiding provocative positions 2

Surgical Management

Indicated when conservative measures fail or in cases with significant vascular compromise:

• Thoracic Outlet Decompression (TOD):

  • Complete first rib resection
  • Scalene muscle transection
  • Neurolysis/venolysis/arteriolysis as needed 3

• Surgical Approaches:

  • Transaxillary approach
  • Supraclavicular approach
  • Paraclavicular approach (primarily for venous TOS) 3

Post-Surgical Rehabilitation

• Early Phase: Passive and assisted mobilization of the shoulder immediately post-surgery 2
• Later Phase: Resistance strength training starting at 8 weeks postoperatively 2

Clinical Pearls and Pitfalls

• Diagnostic Challenge: TOS is often underdiagnosed with an estimated prevalence of only 10 per 100,000 people 2
• Delayed Diagnosis: Diagnosis delayed beyond 14 days significantly worsens outcomes 2
• Subclavian Steal: Syncope associated with upper extremity exercise in subclavian steal syndrome may warrant surgery or angioplasty 1
• Surgical Complications: Include injury to subclavian vessels, brachial plexus injury, hemothorax, and pneumothorax 4
• Multidisciplinary Approach: Management requires coordination between vascular surgeons, neurologists, and rehabilitation specialists 5

Differential Diagnosis

When evaluating syncope in a patient with suspected TOS, consider other causes:

• Cardiac arrhythmias
• Structural heart disease
• Orthostatic hypotension
• Vasovagal syncope
• Neurological disorders 1

TOS-related syncope should be suspected particularly when symptoms occur with arm positioning or exercise and are accompanied by other upper extremity neurovascular symptoms.