Predicting acute denervation in carpal tunnel syndrome.

OBJECTIVE

To determine which nerve conduction parameters can predict the presence of acute denervation in carpal tunnel syndrome.

SETTING

The electrodiagnostic laboratories of a hospital and a county hospital district.

DESIGN

A retrospective review.

PATIENTS: A total of 1,590 consecutive cases from January 1992 to June 1996, diagnosed as having median neuropathy at the wrist.

MAIN OUTCOME MEASURES: Evidence of acute denervation on needle electromyography of the abductor pollicis brevis and its relationship to patient age, gender, and parameters obtained from nerve conduction studies, including median sensory latency and amplitude, and median motor latency and amplitude.

RESULTS

Logistic regression analysis identified gender, median motor latency, and median motor amplitude (all p < or = .008) as contributing to the prediction of denervation. Needle examination of the cases with a median motor amplitude <7 mV detected 95.3% (141/148) of all cases with denervation and could have spared 52% (708/1,362) of the population from a needle examination of the abductor pollicis brevis.

CONCLUSION

The median motor amplitude can predict the presence of acute denervation in the thenar muscles in median neuropathy at the wrist and possibly eliminate a painful needle examination of the median-innervated thenar muscles in over 50% of the cases.