Medial antebrachial cutaneous nerve conduction in true neurogenic thoracic outlet syndrome.

Thoracic outlet syndrome (TOS) and its diagnosis have been topics of controversy, fueled in part by the lack of an objective test for early diagnosis. True neurogenic TOS results in diagnostic EMG findings only in its later stages. We describe a series of patients in whom the diagnosis is supported by changes in the medial antebrachial cutaneous (MAC) nerve at or before the development of these typical EMG findings in median and ulnar nerves.