A comparison of the ultrasonographic median nerve cross-sectional area at the wrist and the wrist-to-forearm ratio in carpal tunnel syndrome

Background: Electrophysiologic (EDX) study is the most valuable method in grading the severity of carpal tunnel syndrome (CTS), but it is invasive and painful. We evaluated the efficacy of ultrasound for this purpose. Materials and Methods: Eighty-one wrists of 52 consecutive patients with clinical evidences of CTS, confirmed and graded by EDX as mild, moderate, and severe, were examined by ultrasonography. Cross-sectional area (CSA) of the median nerve was measured at the distal wrist (CSA-D), and proximal forearm (CSA-P), and wrist-to-forearm ratio (WFR) was calculated for each hand. Results: The mean CSA-D was 0.12 cm2 ± 0.03, 0.15 cm2 ± 0.03 and 0.19 cm2 ± 0.06 and the mean WFR was 2.77 ± 1.14, 3.07 ± 1.07 and 4.07 ± 1.61 in mild, moderate and severe groups respectively. WFR showed significant differences between the severe and none severe CTS groups (P < 0.001), but there was no significant difference between mild and moderate CTS groups (P < 0.381). CSA-D showed a significant difference between all groups (P < 0.0001). In the Receiver Operating Characteristic curve analysis, the optimal cut-off value of the CSA-D and WFR for detecting severe CTS were 0.15 (area under the curve 0.784, 95% confidence interval (CI): 0.662-0.898, P < 0.001, sensitivity of 68.2% and specificity of 70.9%) and 3 (area under the curve 0.714, 95% CI: 0.585-0.84, P = 0.001, sensitivity of 68.2% and specificity of 64.8%) respectively. All values were superior in CSA-D. Conclusion: Ultrasonography, can be complementary but not conclusive to the classification of CTS severities. CSA-D and WFR both increased in proportion to CTS severity, but neither parameter exhibited excellent performance in grading the severities.