Comparison of motor conduction techniques in the diagnosis of carpal tunnel syndrome.

Objective: To compare the sensitivities of motor wrist-to-palm (W-P) conduction velocity and two median-ulnar motor latency differences with that of sensory W-P conduction velocity in the diagnosis of carpal tunnel syndrome (CTS).
Methods: This study included 116 consecutive patients with CTS (160 hands) referred for evaluation and 100 volunteers who served as controls. Median motor and sensory nerve responses with wrist and palm stimulation allowed for the determination of motor and sensory W-P CV (W-P MCV and SCV). Two motor distal latency (MDL) differences between the median-thenar and ulnar-hypothenar (M-U) muscles and between the median-second lumbrical and ulnar-interossei muscles (2L-INT) were measured and calculated. The mean values of controls plus or minus 2.5 SD served as the normal limits.
Results: Among the 160 hands with suspected CTS, 11 (6.88%) had normal electrodiagnostic studies and 149 (93.1%) had at least one abnormal electrodiagnostic study. Among the 149 hands with an abnormality, 139 (86.88%) had abnormal W-P MCV and 129 (80.63%) had abnormal W-P SCV. The sensitivity for 2L-INT was 77.5%, and it was 70% for M-U, 68.75% for median MDL, and 73.75% for sensory distal latency. Combining W-P MCV and W-P SCV allowed for the detection of abnormalities in 147 hands (91.88%) and yielded a markedly improved diagnostic rate compared with W-P SCV alone.
Conclusion: Motor W-P conduction study is more valuable and no more difficult than sensory W-P conduction study for the diagnosis of CTS. In patients with suspected CTS in whom the results of conventional nerve conduction studies are normal, studying both motor and sensory W-P conduction increases the diagnostic yield.