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The term thoracic outlet syndrome (TOS) refers to a heterogeneous group of disorders, all of which have in common compression of one or more neurovascular elements at some point within the thoracic outlet. Of the five disorders comprising this group, four have all of the features expected of a syndrome—a recognized constellation of clinical features; an anatomic derangement accounting for these features; and a method of testing that identifies the anatomic derangement. Consequently, their recognition and management are relatively straightforward. Conversely, one of these five disorders (nonspecific TOS) lacks these correlations, which has generated considerable debate in the literature and caused some experts to doubt its existence altogether. The primary focus in this study is on the neurologic forms of TOS. However, for completeness and a better understanding of these neurologic manifestations, the vascular forms are also reviewed. Muscle Nerve 45: 780–795, 2012

Droopy shoulder has been proposed as a cause of thoracic outlet syndrome. Two patients developed manifestations of neurovascular compression upon arm abduction, associated with unilateral droopy shoulder and trapezius muscle weakness caused by iatrogenic spinal accessory neuropathies following cervical lymph node biopsies. The first patient developed a cold, numb hand with complete axillary artery occlusion when his arm was abducted to 90 degrees. The second patient complained of paresthesias in digits 4 and 5 of the right hand, worsened by elevation of the arm, with nerve conduction findings of right lower trunk plexopathy (low ulnar and medial antebrachial cutaneous sensory nerve action potentials). Spinal accessory nerve grafting (in the first patient) coupled with shoulder strengthening physical exercises in both patients resulted in gradual improvement of symptoms in 2 years. These two cases demonstrate that unilateral droopy shoulder secondary to trapezius muscle weakness may cause compression of the thoracic outlet structures.

This review is an objective critique of the thoracic outlet syndrome, with emphasis on the need to separate true neurogenic and vascular syndromes from nonspecific ones. Major controversies in the diagnosis and management of thoracic outlet syndromes are discussed, with an analysis of major pitfalls encountered in the diagnosis and treatment of patients with nonspecific syndromes. Recommendations to improve diagnostic methods in patients with chronic neurovascular abnormalities in the upper extremities are outlined.