Diagnostic value of ultrasonography using median nerve-tunnel index in patients with carpal tunnel syndrome

This study aimed to evaluate the diagnostic value of ultrasonographic median nerve cross-sectional area and median nerve-tunnel indices comparing to nerve conduction study (NCS) test in patients with carpal tunnel syndrome (CTS). eventy-one hand with clinical symptoms of CTS and fifty-five healthy hands were participated in the study. The cross sectional areas of the median nerve and carpal tunnel in proximal and distal of carpal tunnel were obtained by ultra sonography. The proximal and distal nerve/tunnel indices were obtained by calculating the ratio between the proximal and distal cross-sectional areas of the median nerve to those of the carpal tunnel. The mean of nerve-tunnel index in the distal and proximal were significantly different between patients with CTS and normal (p>0.001). The study showed no difference between the proximal and distal nerve/tunnel index and also between nerve-tunnel Index and median nerve cross-sectional area. Designated cut-off points of proximal nerve-tunnel index for mild, moderate and severe CTS was determined at 6.34, 6.36 and 6.76 with a diagnostic sensitivity of 47.4, 75.8 and 85.7%, respectively, while the cut-off point of distal nerve-tunnel Index was 6.58, 6.58 and 7.61with a diagnostic sensitivity of 47.4, 67.6 and 78.6%, respectively. The results showed that the nerve/tunnel index is not a reasonable replace for NCS technique, due to its low sensitivity and specificity, especially in mild cases. Also, our study showed no significant difference between using ultra sonography nerve-tunnel index and median nerve cross-sectional area in the diagnosis of CTS.