Use of diffusion tensor imaging as a prognostic biomarker after decompression surgery for carpal tunnel syndrome

Magnetic resonance diffusion tensor imaging (MR-DTI) has been increasingly applied for carpal tunnel syndrome (CTS) diagnosis, but relatively little is known about the effect of CTS treatment on median nerve (MN) integrity and functional outcome prediction.

To assess how structural changes in MR-DTI of the MN correlates with symptom severity, functional status, and electrophysiological parameters in patients suffering from CTS before and after decompression surgery.

Nine wrists were prospectively enrolled to perform MR-DTI pre- and postoperatively. The apparent diffusion coefficients (ADC) and fractional anisotropy (FA) of the MN were examined in three different regions-distal radioulnar joint, pisiform bone, and hamate bone-and correlated with clinical and electrophysiological parameters.

Postoperatively, mean Boston Carpal Tunnel Questionnaire scores decreased 1.55 points (range = 0.08-3; P = 0.0172) and 1.01 points (-0.13 to 1.88; P = 0.0381) in the symptomatic and functional domains, respectively. Postoperative clinical improvement was reflected in proximal FA elevation (P = 0.0078), but not in diffusivity in comparison to baseline examination. Preoperative electrophysiological parameters were correlated with a reduction in the pre- (sensory latencies [rho = -0.6826; P = 0.0312]) and postoperative (motor latencies [rho = -0.7488; P = 0.0325]) distal FA values. Higher sensory amplitudes indicated higher postoperative proximal FA values (rho = 0.7618; P = 0.0280) ​​and lower postoperative proximal ADC values (rho = -0.9047; P = 0.0020).

Our study demonstrated that pre- and postoperative proximal FA values are useful biomarkers for the structural evaluation of the MN in patients with CTS. Symptomatic improvement can be better predicted by analyzing FA changes.