THE UTILITY OF VARIOUS SENSORY NERVE-CONDUCTION RESPONSES IN ASSESSING BRACHIAL PLEXOPATHIES

To determine which sensory nerve conduction studies (S-NCS) are helpfu l in detecting supraclavicular axon loss brachial plexopathies, we sel ected 53 cases (of 417 reviewed) in whom complicating factors were abs ent and which, by needle electrode examination findings, involved only a single ''truncal'' element (upper, middle, or lower) of the brachia l plexus, Extensive S-NCS included: median, recording thumb (Med-D1), index (Med-D2), and middle fingers (Med-D3); ulnar, recording fifth fi nger (Uln-D5); dorsal ulnar cutaneous, recording dorsum of the hand (D UG); radial, recording base of thumb; and both medial and lateral ante brachial cutaneous (MABC, LABC), recording forearm. Except for the med ian sensory fibers, the ''cord'' elements traversed by the sensory fib ers assessed during the S-NCS listed above are anatomically defined (i .e,, the sensory fibers enter the brachial plexus at only one cord), I n regard to the median sensory fibers, however, there are two possible pathways through the infraclavicular plexus: (1) the lateral cord and /or (2) the medial cord, Because the lower trunk is only accessible vi a the medial cord, any sensory fibers found to be traversing the lower trunk had to first traverse the medial cord. Similarly, those travers ing the upper and middle trunks must first be a component of the later al cord. The frequency that the various S-NCS responses were abnormal (unelicitable, below laboratory normal value, or less than or equal to 50% of the contralateral response) for a given brachial plexus elemen t lesion was as follows: (1) upper trunk (UT): 25 of 26 Med-D1, 25 of 26 LABC, 15 of 26 radial, 5 of 26 Med-D2, 2 of 26 Med-D3; (2) middle t runk (MT): 1 of 1 Med-D3; (3) lower trunk (LT): 25 of 26 Uln-D5, 22 of 23 DUC, 11 of 17 MABC, 3 of 23 Med-D3. With lower trunk brachial plex opathies, both ''routine'' (Uln-D5) and ''uncommon'' (DUC; MABC) S-NCS are abnormal. With upper trunk brachial plexopathies, in contrast, on ly the ''uncommon'' S-NCS (Med-D1; LABC) are consistently affected. Th e ''routine'' median S-NCS recording digit 2 (Med-De) is far less reli able than the median S-NCS recording digit 1 (Med-D1) in detecting upp er trunk axon loss brachial plexopathies. Additionally, the various pa thways traversed by the fibers contributing to the individual S-NCS re sponses can be predicted, an important point when the full extent of a brachial plexus lesion is sought. (C) 1995 John Wiley and Sons, Inc.