Thoracic Outlet Syndrome
TOS is a non-specific diagnosis referring to compression of one or more of the neurovascular structures within the thoracic inlet. Diagnostic terminology is currently based on the structure that is compressed (eg. neurogenic TOS, venous TOS, arterial TOS, and mixed TOS), rather than the site of compression.
Neurogenic TOS is felt to comprise >95% of all TOS subtypes. Symptoms typically involve the neck and medial arm though paresthesias may also present in the lateral arm. Patients often report trauma or repetitive stress as the causative factor.
Venous TOS comprises 2-3 % of TOS subtypes. Venous TOS is also called effort thrombosis or Paget-Schrotter disease. One may detect acute swelling. cyanosis and distended superficial veins over the shoulder and chest wall, along with heaviness, paresthesias and effort dependent pain. The risk of pulmonary embolus necessitates aggressive treatment intervention.
Arterial TOS makes up less than 1% of TOS cases and results form compression of the subclavian artery. If arterial embolization occurs, patients will have hand and finger pain, paresthesias, coldness and ischemic colour changes. Abnormal ribs are noted in 74-100% of surgical cases.
Potential Neurovascular Compression Sites
- The Interscalene Triangle
Bounded by the first rib below, the anterior scalene muscle anteriorly and the middle scalene muscle posteriorly. Compression in this triangle may result from muscular injury (eg. cervical whiplash), hypertrophy (eg. repetitive overhead activity), fibromuscular bands and cervical or anomalous thoracic ribs. The subclavian vein is not contained in this triangle
- The Costoclavicular Space
As the name implies, this space is located between the clavicle and the first rib. The space is reduced during shoulder abduction as the clavicle moves inferiorly. Any of the neurovascular structures may be compressed in this region.
- The Retropetoralis Minor Space
The pectoralis minor muscle extends from the coracoid process of the scapula to ribs 3,4, 5. The volume of this space is also reduced during hyperabduction of the arm because the tendon and coracoid may create a fulcrum around which the neurovascular structures must change directions.
Clinical Diagnostics
Swelling and cyanosis due to subclavian vein obstruction will not be observed in arterial or neurogenic TOS. The following tests may duplicate symptoms and help establish the diagnosis:
1. Head rotation and side flexion may elicit symptoms down the contralateral side.
2. Abduction of the arms to 90 in external rotation will bring on symptoms within 60 seconds. In the Modified Roos version of this test, the patient is asked to additionally open and close the hands for up to 3 minutes.
3. The Modified Upper Limb Tension Test has the patient actively performing the following progressions of brachial plexus stretch:
3.i) Abduction of arms to 90
3.ii) Dorsiflexion of wrists
3.iii) Side flexion of head
Sanders et al. suggest that arterial TOS will often present with absent radial pulse at rest and will lack the scalene muscle tenderness seen with the more common neurogenic type. Absence of a cervical or anomalous first rib on X-ray will essentially rule out arterial TOS. Presence of an anomalous rib does not by any means rule out neurogenic TOS.
The success of conservative physiotherapy treatments on cervicoscapular complaints has decreased the number of surgical decompressions required. Non vascular forms of TOS should begin conservatively, though some exercise programs take 6 months to achieve results.
References:
1. Povlsen B, Belzberg A, Hansson T, Dorsi M. Treatment for thoracic outlet syndrome. Cochrane Database of Systematic Reviews 2008, Issue 3. Art. No.: CD007218.
2. Nichols AW. Diagnosis and Management of Thoracic Outlet Syndrome. Current Sports Medicine Reports, American College of Sports Medicine, 2009:240-9.
3. Sanders RJ, Hammond SL, Rao NM. Diagnosis of Thoracic Outlet Syndrome. Journal of Vascular Surgery, Sept. 2007;46:601-4.