Thoracic Outlet Syndrome
Thoracic outlet syndrome (TOS) is a poorly characterized disease entity with a wide differential diagnosis. First coined in 1956 by Peet et al, TOS can be categorized as vascular (arterial or venous) or neurogenic (NTOS). Although vascular-related TOS pathology is intuitively easier to understand and document because of more definitive imaging findings and symptoms, there remains significant controversy as to even the existence of NTOS.
The anatomic issue in TOS occurs as the result of compression of the neurovascular bundle (brachial plexus, subclavian artery, and subclavian vein) at the transition between the neck and axilla just above the first rib. Neurogenic TOS is much more common than vascular TOS, with most single center series reporting ratios of 20 to 1. Symptoms of NTOS referable to the upper extremity occur because of compression of the lower trunk of the brachial plexus caused by a cervical rib or band and enlarged scalene muscles.
Classically described or “true” NTOS with strict diagnostic criteria was outlined by Gilliatt et al in 1974 , but unfortunately, most reported series of NTOS to date rarely meet these criteria. Symptoms typically include arm discomfort, paresthesias of the inner surface of the hand and forearm, and weakness and atrophy of the thenar and intrinsic hand muscles of the affected side. Distinct anatomic and electrophysiologic findings include low compound muscle action potentials in the thenar and intrinsic muscles, abnormal sensory conduction of the ulnar nerve, prolonged F-wave latency of the ulnar nerve, and abnormal sensory conduction of the medial antebrachial cutaneous nerve.