Median nerve compression at the wrist: is it ever unilateral?

OBJECTIVE

Carpal Tunnel Syndrome (CTS) is commonly bilateral, but symptoms and EMG/NCS abnormalities may be seen unilaterally. This study was designed to determine whether there are any subclinical nerve conduction abnormalities on the "uninvolved" side.

DESIGN

Statistical analysis of electrodiagnostic data.

SETTING

Outpatient academic electrodiagnostic laboratory.

PATIENTS: Twenty-two successive patients referred for bilateral upper extremity NCS/EMG with no symptoms or physical signs of CTS and totally normal results, and ten successive patients with an EMG/NCS diagnosis of CTS on one side, and completely normal EMG/NCS on the contralateral side.

RESULTS

The median motor and sensory latencies at the wrist were significantly longer in the contralateral "uninvolved" limb than normals (median motor latency 3.75 vs. 3.30 msecs, p = 0.0005, median sensory latency 3.40 vs 3.00 msecs, p = 0.0002). Median sensory amplitude was smaller in the contralateral limb (30.5 uV vs. 41.5 uV, p = 0.0062). The (median-radial) D1 sensory latency difference was greater in the contralateral wrist (0.2 vs. 0.0 msecs, p = 0.0217). The (median-ulnar) sensory latency difference was not significantly increased (0.15 vs. 0.10 msecs, p = 0.2020).

CONCLUSIONS

The contralateral limbs of patients with unilateral CTS show significant differences from normals in 4 out of 5 nerve conduction parameters. There is evidence of frequent subclinical median nerve compression in this group.