Optimal parameters and location for diffusion-tensor imaging in the diagnosis of carpal tunnel syndrome: a prospective matched case-control study.

Abstract

The purpose of this study was to determine the optimal parameters and location for diffusion-tensor imaging in the diagnosis of carpal tunnel syndrome. A single 3-T MRI (single-shot echo-planar imaging pulse sequence; b value, 1000 s/mm(2)) and nerve conduction study were performed prospectively for patients with carpal tunnel syndrome and age- and sex-matched control subjects. Fractional anisotropy, apparent diffusion coefficient, radial diffusivity, and parallel diffusivity of the median nerve were measured at the inlet, middle, and outlet of the carpal tunnel and were compared with the nerve conduction study parameters. A total of 50 patients with carpal tunnel syndrome and 50 control subjects were enrolled. Demographic data were comparable between the groups. For all three locations, mean fractional anisotropy increased significantly, and the mean radial diffusivity and apparent diffusion coefficient decreased significantly in carpal tunnel syndrome (p < 0.05). The carpal tunnel inlet had the largest and most consistent changes in diffusion-tensor imaging parameters. Fractional anisotropy measured at the carpal tunnel inlet had the highest diagnostic accuracy, as measured with ROC curves (AUC, 0.82). For a fractional anisotropy threshold of 0.44 or less at the carpal tunnel inlet, sensitivity was 72%; specificity, 82%; positive predictive value, 80%; and negative predictive value, 75%. The use of fractional anisotropy measured at the carpal tunnel inlet is optimal for diagnosing carpal tunnel syndrome.