MRI criteria for diagnosis and predicting severity of carpal tunnel syndrome

To study MRI criteria for diagnosing and predicting severity of carpal tunnel syndrome (CTS).

Sixty-nine wrists in 41 symptomatic CTS patients and 32 wrists in 28 asymptomatic subjects were evaluated by MRI. Circumferential surface area (CSA), flattening ratio, relative median nerve signal intensity, and retinacular bowing were measured. CTS severity was classified as mild, moderate, or severe. Parameters for patients with and without CTS and for the three severity groups were compared. ROC curves were plotted to assess accuracy for CTS diagnosis and severity prediction.

Significant differences were found between CTS and control wrists for median nerve CSA, flattening ratio at inlet, relative median nerve signal intensity, and retinacular bowing. ROC curve analysis revealed a sensitivity, specificity, and accuracy of median nerve CSA > 15 mm² proximal to the tunnel (CSA_p) of 85.5, 100, and 90.1%. Using either CSA_p or CSA_d > 15 mm² as a diagnostic criterion, MRI could achieve a sensitivity of 100% and specificity of 94% for diagnosis of CTS while overall accuracy was 98%. Significant differences were found among the three severity groups. Sensitivity, specificity, and accuracy of prediction of severe CTS using for CSA_p > 19 mm² were 75.0, 65.9, and 69.6%, respectively.

MRI is highly accurate at diagnosing CTS and moderately accurate at determining CTS severity. We recommend using CSA > 15 mm² either proximal to or distal to the tunnel as a diagnostic criterion for CTS and CSA > 19 mm² proximal to the tunnel as a marker for severe CTS.