Neurogenic Thoracic Outlet Syndrome
Neurogenic thoracic outlet syndrome (TOS) is one of the most controversial pain disorders of the upper extremity. Difficulty arises in the effective diagnosis and then classification of the true and subjective forms of TOS. The condition itself is a clinical manifestation resulting from compression of the neurovascular bundle in the thoracic outlet. Potential sites of compression within the outlet have been identified as: the interscalene triangle, costoclavicular space and the subpectoral tunnel. True neurogenic subtypes are rare (1 per 1 million) and present with clear clinical signs of nerve compression. In contrast, subjective subtypes of neurogenic TOS tend to be the vast majority and they present with non-specific clinical findings.
Etiologically, three main causes of true neurogenic TOS can be identified. Structural abnormalities are identified in all cases and include anatomical variants of osseus, fibrous and fibro-muscular structures. Post-traumatic TOS can result from the loss of costoclavicular space as a result of damage or secondary to central sensitization or trauma-induced fibrosis. Lastly, acquired cases tend to be associated with repetitive overuse and postural dysfunction resulting in intermittent nerve compression at the thoracic outlet and/ or double-crush syndromes. Diagnosing true (neurogenic) TOS is by the presence of muscle atrophy and wasting in the lateral thenar musculature in conjunction with associated pain in the medial aspect of the upper limb.
When diagnosing subjective TOS, the Roos test and upper limb tension test can be used to recreate symptomology. Palpation and physical examination of the anterior scalene, brachial plexus and subpectoral space should all be performed to rule out myofascial referred pain. Trigger points in the scalenes (particularly anterior) can cause deep somatic pain with referred paresthesia to the hand that mimics TOS.
Treatment of TOS should always begin with conventional therapy consisting of addressing underlying postural and repetitive use conditions. For instances of true TOS surgery is almost always necessary, however subjective forms of TOS are often managed with traditional stretching and strengthening programs. Clinicians should also consider the use of manual therapy to reduce the involvement of myofascial tension and referred pain.