The value of special motor and sensory tests for the diagnosis of benign and minor median nerve lesion at the wrist.

Four special tests to assess benign and minor median nerve lesion at the wrist (MLW) were evaluated in 40 controls and three groups of 25 carpal tunnel syndrome with different degrees of orthodromic sensory conduction velocity (OSCV) slowing. The motor tests were the median-ulnar distal latency difference of the thenar muscles and the second lumbrical-interossei distal latency difference. They were abnormal in only 20% and 4% of patients, respectively, in group 1 (OSCV > 45 m/s), in 56% and 60% in group 2 (45 m/s > OSCV > 40 m/s), and were both abnormal in 96% of patients in group 3 (OSCV < 40 m/s). The two sensory tests were the median-ulnar orthodromic sensory latency difference of the fourth digit and the centimetric technique; they were abnormal in 80% and 96% (group 1) and in 96 and 100%, respectively (group 2). All things considered, only the sensory tests showed a satisfactory efficacy to assess benign and minor MLW, because the motor tests reached a positivity of 96% only in group 3.