Second lumbrical and mixed nerve segmental conduction studies in carpal tunnel syndrome.

OBJECTIVES

We report the findings of 20 patients with carpal tunnel syndrome (CTS) who had segmental motor studies to the second lumbrical (2L) and mixed nerve action potential (MNAP) across the carpal tunnel.

METHODS

This was a prospective study of 20 patients randomly selected who had clinical and electrophysiologic evidence of CTS using standard techniques. Six CTS patients had studies pre- and post-surgical release.

RESULTS

Mean 2L motor amplitude reduction across the carpal tunnel was 55.19% ± 6.6% in patients (controls = 15.9% ± 9.4%). Mean motor velocity across the carpal tunnel was 23.4 ± 7.05 m/s versus 46.45 ± 6 m/s in controls. Mean reduction of the MNAP amplitudes was 79.0% ± 23% versus 20% ± 15% in controls. The mean MNAP velocity was 12.3 ± 13.1 m/s versus 48.35 ± 5.18 m/s in controls. The 6 surgical cases showed improvement in amplitude reduction and velocity at 2-6 months consistent with preoperative severity.

CONCLUSIONS

These studies show that segmental conduction studies to the 2L and MNAP can demonstrate conduction block that improves with decompression.