Wrist Circumference-Dependent Thresholds for the Median Nerve in Carpal Tunnel Syndrome: A Cross-Cohort Comparison.

Background: Considerable between-center variability exists in the upper limit of normal (ULN) for the cross-sectional area (CSA) of the median nerve (MN) used to support the diagnosis of carpal tunnel syndrome (CTS). Objective: To evaluate whether a Dutch wrist circumference-dependent (WCD) equation for the ULN of MN CSA provides comparable classification of abnormal CSA in Italian and Dutch CTS populations. Methods: Wrist circumference (WC) and MN CSA were measured in 55 Italian (85 wrists) and 175 Dutch (175 wrists) patients with CTS. Abnormal wrists were identified using three thresholds: ULN9 (9 mm 2 ), ULN11 (11 mm 2 ), and a WCD equation ( y = 0.88 * x - 4, with y as ULN in mm 2 x as WC in cm). Findings were compared with electrodiagnostic results. Results: No significant differences in WC or MN CSA were observed between groups. The proportion of abnormal wrists in the Italian and Dutch populations, respectively, was 83.5 and 78.3% (ULN9, p = 0.321), 49.4 and 50.3% (ULN11, p = 0.895), and 61.1 and 55.4% (WCD, p = 0.379). Among 12 Italian patients with small wrists, abnormal results were found in 75.0% (ULN9), 25.0% (ULN11), and 66.7% (WCD). All Italian patients had abnormal electrodiagnostic testing results, compared with 66.3% of Dutch patients ( p < 0.0001). Conclusion: The WCD ULN for MN CSA yielded similar results in Italian and Dutch patients with CTS, and may be particularly useful in individuals with smaller wrists.