Thoracic Outlet Syndrome: Diagnosis [Clinical Review Discussion]

Thoracic outlet syndrome is the center of a raging controversy in the healthcare field.  Vanti et al stated “Thoracic outlet syndrome (TOS) has been one of the most debated clinical topics over the last 120 years” (1).  Some experts feel it is over-diagnosed (2) while others think it is under-diagnosed (3).  The fact that 120 TOS surgeries were performed at the Mayo Clinic over a 34 year period while in less than half of that time a single Colorado thoracic surgeon performed 1400 TOS surgeries is indicative of the controversy relating to TOS (4).  Cherington in an editorial states the disputed form of TOS “in which no objective clinical, radiologic or electrodiagnostic abnormalities are documented, is the most commonly diagnosed and surgically treated form of TOS” (5).  This form of TOS represents 85% (1) to 95% (6) of all TOS cases.  Based on a large majority of opinions TOS is almost always a clinical diagnosis without confirming objective evidence.

Thoracic outlet syndrome (TOS) results from compression of the neurovascular structures as they pass through the thoracic outlet, primarily the interscalene triangle, the costo-clavicular space and the subpectoral tunnel.  Some authors also include the area anterior to the humeral head, passageway for the median nerve roots and the axilla (1).  Thoracic outlet syndrome is usually categorized as follows (7):

1. Neurogenic TOS:  Represents up to 95% of all TOS cases and has two subcategories.
   
   a.  True Neurogenic TOS:  Patients present with subjective symptoms which can be confirmed by objective testing.  According to Burke this form is “as rare as rocking-horse manure” (8)
   
   b.  Disputed Neurogenic TOS:  Patients present with subjective complaints which cannot be objectively confirmed,  The subjective symptoms often include upper extremity heaviness, fatigability, neck, face and shoulder pain and extremity paresthesias. These cases represent up to 99% of neurogenic TOS.
   
2. Venous TOS:  These cases are characterized by swelling of the upper extremity, heaviness, pain with activity and paresthesias.  They represent 2 to 3% of TOS cases.
   
   
3. Arterial TOS:  This is the least common form and represents less than 1% of TOS patients.  Pain, paresthesias, cyanosis, fatigability, coldness and color changes are common presentations.  Arterial TOS is often asymptomatic until an embolism occurs. 

The difficulty in diagnosis of TOS by provocative tests is demonstrated in the high number of positive results in asymptomatic populations.  Rayan et al found 91% of normal volunteers had a positive response to at least one of three provocative tests (hyperabduction, Adson’s and costo-clavicular tests) (9).  A 1980 photoplethysmographic study found 60% of a normal population, when tested with provocative maneuvers, had arterial obstruction (10).

The reader should be aware that generally less than 5% of patients with TOS can be identified with provocative testing.  The overwhelming majority must be diagnosed based on history and complaints after ruling out other causes.  Thoracic outlet syndrome is primarily an exclusion diagnosis. It should be noted that carpal tunnel syndrome (CTS) often manifests similar symptoms as TOS.  Nord et al found that many of the TOS tests also test positive in patients with CTS.  This results in a high false positive rate for TOS in many patients with CTS (11).  This is troublesome since the first step in the diagnostic process is often to rule out CTS (12;13). 

The typical TOS patient is female, between 20 and 50 years old, has a history of neck trauma and complains of arm pain and paresthesias (14).