[The value of motor latency difference measurements between the second lumbrical muscle and second interosseous muscle in the diagnosis of carpal tunnel syndrome].

The aim of the study was to evaluate the sensitivity of a new electrophysiological test determining the difference between distal motor latencies of the second lumbrical and the second interosseous muscles (2LIDML test) in patients with carpal tunnel syndrome (CTS). We examined 161 nerves of 100 patients with clinical CTS symptoms, including 68 women and 32 men, aged from 20 to 84, as well as 60 nerves in the healthy control group. The 2LI-DML test examination results were compared with standard test results and an additional D4M-D4U test. The 2LI-DML test is based on the comparison between the median motor distal latency in the motor fibres, at the distance wrist-second lumbrical muscle, and the ulnar nerve latency, at the distance wrist-second interosseous muscle, maintaining identical distances during nerve stimulation and placing the recording electrode between the second and third metacarpal. The mean latency difference in 2LI-DML test in the control group was 0.15 ms + 0.12 (mean +/- SD), while the upper range limit was established at 0.4 ms (mean + 2SD). Abnormal 2LI-DML test result was found in 89% of patients, that of D4M-D4U in 88% of patients, and that of standard tests in 74% of patients. Our evaluation of results demonstrates that the 2LI-DML test is a very sensitive and useful method for the diagnosis of a severe damage of median nerve, when the application of standard methods does not allow to obtain sensory and motor responses.