LUMBRICAL-INTEROSSEOUS LATENCY COMPARISON IN THE DIAGNOSIS OF CARPAL-TUNNEL SYNDROME

We examined 66 hands referred with suspected carpal tunnel syndrome (C TS) using the second lumbrical-interosseous distal motor latency diffe rence (2LI-DML) as well as standard tests. Forty-nine cases of CTS wer e diagnosed by the standard tests, 48 of whom had an abnormal median-u lnar palmar velocity comparison and 48 an abnormal 2LI-DML. The result s of these 2 tests were closely correlated. The 2LI-DML supported the diagnosis of CTS in all cases except one, where the result was borderl ine. In one suspected case the 2LI-DML was the only abnormality. In 9 severe cases no median palmar responses could be obtained but an abnor mal 2LI-DML was found. We conclude that the 2LI-DML is as sensitive as the palmar comparison and thus will support the diagnosis of CTS made by standard tests by providing an additional abnormality but that its routine use is unlikely to increase the diagnostic yield. Its value t herefore may be in mild cases where the median-ulnar palmar comparison is normal or equivocal and in severe cases where standard test respon ses are unobtainable. It has also proved useful as a quick and simple screening test for CTS on the asymptomatic side.