Ultrasound carpal tunnel syndrome: additional criteria for diagnosis

To define the usefulness of the cross-sectional area (CSA) of the median nerve distal to the carpal tunnel in addition to other established common parameters in the diagnosis of carpal tunnel syndrome (CTS).

Forty-four wrists from 24 symptomatic CTS patients and 32 wrists from 17 asymptomatic volunteers were evaluated by ultrasound. The CSA of the median nerve was measured at four pre-selected levels, i.e., proximal, inlet, outlet, and distal to the carpal tunnel. The flattening ratio, intraneural vascularity, neural fasciculation, and retinacular palmar bowing were also assessed.

Significant differences were found between the CTS and control groups for median nerve CSA proximal and distal (p<0.001) to the tunnel as well as retinacular bowing (p<0.001). Using the receiver operating characteristic (ROC) curve, the sensitivity, specificity, and accuracy of using a cut-off of >14 mm² of CSA proximal and distal to the tunnel were 75%, 87.5%, 86.8% and 63.6%, 100%, 78.9%, respectively. Using either CSA proximal or distal to the tunnel or bowing retinaculum at the outlet >1 mm yielded a sensitivity, specificity, and accuracy of 100%, 84.3% and 93.4%, respectively.

The median nerve CSA proximal and distal to the carpal tunnel and bowing of the retinaculum at the outlet are helpful in diagnosis of CTS.