Frequency of neurogenic thoracic outlet syndrome in patients with definite carpal tunnel syndrome: an electrophysiological evaluation in 100 women.

OBJECTIVE: The aim of this work was to evaluate the frequency of lower brachial plexus lesions as true neurogenic thoracic outlet syndrome (NTOS) in women with carpal tunnel syndrome (CTS).

METHODS: This was a prospective and descriptive study. The CTS was clinically and electrodiagnostically defined in each patient. The conduction of ulnar and medial antebrachial cutaneous nerves (MABCN) was bilaterally studied to evaluate the function of lower brachial plexus. One hundred women with 176 median nerve lesions at wrist were studied. Patients with ulnar nerve lesion at elbow or wrist were excluded. The sensory nerve action potential (SNAP) of ulnar nerve was abnormal when the interside amplitude ratio was greater than 1.66 or when its amplitude was smaller than 8 microV. The SNAP of MABCN was abnormal when the interside amplitude ratio was greater than 1.66 with both techniques (antidromic and orthodromic) or when its amplitude was smaller than 8 and 6 microV for non-obese patients, respectively, less and more than 60 years old.

RESULTS: The mean SNAP amplitude of ulnar and MABC nerves was normal compared with control subjects, and none of the 100 women with CTS had an abnormal interside amplitude ratio for one or both nerves. In 7-10 cases, all of which were either obese or elderly patients, SNAP amplitude of MABCN was decreased, but the interside amplitude ratio remained normal.

CONCLUSIONS: On the basis of tests considered quite sensitive (70%) and specific (100%), the occurrence of true NTOS is lower than 1/100 in woman with definite CTS.

SIGNIFICANCE: These results demonstrate that there is no appreciable link between CTS and true NTOS. There is no need for the systematic MABCN testing had in CTS patients.