Comparison of sensitivity of transcarpal median motor conduction velocity and conventional conduction techniques in electrodiagnosis of carpal tunnel syndrome.

OBJECTIVE: To compare the sensitivity of median wrist-palm motor conduction velocity (W-P MCV) with those of standard sensory conduction techniques in the electrodiagnosis of carpal tunnel syndrome (CTS).

METHODS: This study included 280 consecutively suspected CTS patients (360 hands) referred for evaluation and 150 volunteers who served as controls. We determined and calculated (1) median W-P MCV, (2) median motor distal latencies (DL) and median sensory DL for (3) thumb (D1), (4) index (D2) and (5) ring finger (D4), (6) median wrist-palm sensory conduction velocity (W-P SCV) and sensory conduction time (W-P SCT) for index finger and sensory latency differences between (7) median-radial (M-R) for thumb and (8) median-ulnar (M-U) nerves for ring finger. The normal limits were calculated from the median of normal controls +/-2.5 standard deviations. The sensitivities of each test were determined and compared.

RESULTS: Among the 360 hands with suspected CTS, 32 hands (8.9%) had normal electrodiagnostic studies and 328 (91.1%) had at least one abnormal electrodiagnostic study. Among the 328 hands with abnormalities, 234 (65%) had abnormal motor DL and 294 (81.7%) had abnormal W-P MCV. The sensitivity was 80.3% for D1, 72.5% for D2, 76.7% for D4, 86.7% for M-R (specificity, 98.7%), 87.2% for M-U (specificity, 96.7%), 80.8% for sensory W-P SCT and 73.6% for W-P SCV.

CONCLUSIONS: W-P MCV is a valuable motor conduction technique for the diagnosis of CTS and it is confirmed again that W-P MCV is equal to or more sensitive than W-P SCV and W-P SCT. Furthermore, the findings of the present study are in agreement with the conventional wisdom that internal comparison of latency differences between median and ulnar or radial nerves is the best method for a diagnosis of patients with suspected CTS. Therefore, we recommend that CTS patients be studied according to the following steps: (1) routine sensory and motor DL, (2) if step 1 is negative, then perform and determine W-P MCV or SCT. This may increase the diagnostic yield of 10%, (3) if step 2 is negative, measure the M-U or MR. These are the final and more sensitive techniques in making a diagnosis with an additional diagnostic yield of 10%.

SIGNIFICANCE: We provide the evidence of W-P MCV that could be a standard technique for electrodiagnosis of CTS. Furthermore, we make a reasonable flow chart and recommendation for electrodiagnosis of CTS for electromyographers.