Cervical rib and median sternotomy-related brachial plexopathies: a reassessment

The objective of this study was to identify electrodiagnostic and anatomic distinctions between true neurogenic thoracic outlet syndrome and median sternotomy-related brachial plexopathy, in reference to the pattern of abnormality of the medial antebrachial cutaneous sensory nerve conduction study (NCS) response.

Neurogenic thoracic outlet syndrome and sternotomy-related brachial plexopathy are both lower trunk brachial plexopathies, but their clinical and electrodiagnostic presentations are distinct. The anatomic differences distinguishing these disorders from each other, and from other lower trunk brachial plexopathies, have not been defined.

We compared the medial antebrachial cutaneous sensory nerve action potential amplitude with the median motor, ulnar motor, and ulnar sensory NCS amplitudes in 10 patients with neurogenic thoracic outlet syndrome and in 14 patients with sternotomy-related brachial plexopathy.

In the 10 patients with neurogenic thoracic outlet syndrome, the medial antebrachial cutaneous amplitude was most affected, followed in decreasing order of involvement by the median motor, ulnar sensory, and ulnar motor amplitudes. Conversely, in the 14 patients with sternotomy-related brachial plexopathy, the ulnar sensory and motor amplitudes were the most affected responses. Medial antebrachial cutaneous NCS changes closely paralleled median motor response changes.

The medial antebrachial cutaneous sensory response is sensitive in the diagnosis of neurogenic thoracic outlet syndrome. Our data suggest that medial antebrachial cutaneous nerve fibers are closely associated anatomically at the T1 root level with median motor fibers innervating the thenar muscles. Neurogenic thoracic outlet syndrome shows predominant damage in the T1 distribution, whereas sternotomy-related brachial plexopathy shows predominant damage in the C8 distribution, suggesting that these lesions are localized at the level of the anterior primary rami of the cervical roots, and not in the lower trunk of the brachial plexus.