The Best Cutoff Point for Median Nerve Cross Sectional Area at the Level of Carpal Tunnel Inlet

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy. It accounts 90% of all entrapment neuropathies all over the world. Ultrasound is a non-invasive, cost effective and available para-clinical method which could be applied for CTS diagnosis. Cross-sectional area of the median nerve at the level of the inlet is considered as a diagnostic criterion in CTS cases. In this study, thirty-eight patients with electrophysiologically confirmed idiopathic CTS and 22 healthy controls were enrolled. Seventy-one affected nerves and 42 unaffected nerves were evaluated within 14 days after electrophysiological examination. The largest cross-sectional area (CSA) was measured at the level of the carpal tunnel inlet and the maximum nerve perimeter was also recorded by means of the software. Mean CSA and perimeter were 14.02 ± 4.5 mm2 and 1.7±0.28m in all patients and 8.2±2.1 mm2, 1.3±0.19 m in controls (P<0.001, P<0.001). Mean CSA and Perimeter were significantly different between patient's groups and control. The best cut off point for CSA of the tunnel inlet was 10.5 mm2 with sensitivity and specificity of 80% and 76% (AUC (Area under the Curve) = 0.9, P<0.001). The best cut off point for inlet perimeter was 1.44 m with sensitivity and specificity of 85% and 77 % (AUC=0.87, P<0.001). Our findings showed that median nerve CSA at carpal tunnel inlet could be used as the diagnostic criteria for CTS.