Improvement of diagnostic rate of carpal tunnel syndrome with additional median-to-ulnar comparative nerve conduction studies.

PURPOSE: The aim of this study is to assess whether additional median -to-ulnar comparative tests will improve the diagnostic rate of carpal tunnel syndrome (CTS).

METHODS

We recruited 248 hands of 162 CTS patients, and 166 hands of 83 controls. One hundred and sixty-eight (68%) symptomatic hands had abnormal median distal latencies or palm-wrist latencies. We performed three additional comparative tests in the remaining symptomatic hands and the non-CTS hands. The first test compared median distal motor latency (MDL) recorded from the second lumbrical muscle (2L) and ulnar distal latency recorded from interossei muscles (INT) (2L-INT). The second test compared median and ulnar antidromic sensory latencies (MS-US). And the third test compared median and ulnar nerve latencies in the palm-to-wrist segment (PM-PU).

RESULTS

In control subjects, upper limits of median-to-ulnar differences were: 2L-INT= 0.4 ms, MS-US= 0.5 ms, PM-PU= 0.4 ms. In CTS patients with normal conventional electrodiagnostic methods, MS-US difference showed the lowest sensitivity (21.3%). The diagnostic sensitivity of 2L-INT was 27.5% and PM-PU 47.5%. With PM-PU test, additional 15.3% diagnostic rate could be got.

CONCLUSION

For CTS patients with normal results from the standard methods, PM-PU is a good additional comparative test to further improve diagnostic rate.