Determination of Electrophysiologically Moderate and Severe Carpal Tunnel Syndrome: Ultrasonographic Measurement of Median Nerve at the Wrist.

OBJECTIVE

To establish the cutoff value of cross-sectional area (CSA) of the median nerve at the wrist, for determination of electrophysiologically moderate and severe carpal tunnel syndrome (CTS).

METHODS

The prospective study was conducted among patients suspected of having CTS. A total of 106 patients (185 symptomatic wrists) received nerve conduction study (NCS) and ultrasonography. To establish a cutoff value, various diagnostic properties were calculated across a range of the CSA.

RESULTS

A mean±standard deviation of CSA of the median nerve of normal and mild, moderate and severe CTS was 9.4±2.1, 12.0±2.7, 13.8±4.7, and 15.4±4.1 mm, respectively. The positive relationship between CTS severities and CSA was observed (rs=0.56). A 14 mm CSA had sufficient power to rule in moderate and severe CTS, with a specificity of 91.4% and sensitivity of 42.3%. In addition, it showed a post-test probability (positive predictive value) of 86.3% as against a pre-test probability of 56.2%.

CONCLUSION

Patients who had ≥14 mm of median nerve CSA had very high probability of moderate to severe CTS.