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

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).

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.

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.

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).

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.