High-resolution MRI predicts steroid injection response in carpal tunnel syndrome patients

Objectives To correlate median nerve T2 signal and shape at the carpal tunnel with steroid injection (SI) response in carpal tunnel syndrome (CTS) patients. Methods One hundred and sixty-three CTS wrists of 92 consecutive patients who were scheduled to undergo SI were prospectively evaluated with 3-T magnetic resonance imaging (MRI) and a nerve conduction study. All patients underwent axial high-resolution T2-weighted MRI (in-plane resolution of 0.25x0.25 mm). The CTS wrists were classified into three groups according to the nerve T2 signal and the flattening ratio at the hook of hamate level: group 1, high and oval; group 2, high and flat; group 3, low and flat. Clinical response to SI was evaluated at 6 months after injection. Results One hundred and thirteen of the 163 wrists (69.3 %) responded well to SI. The percentage of improvement was 81.7 % (49/60) in group 1, 69.9 % (51/73) in group 2, and 43.3 % (13/30) in group 3 (P < 0.01). On stepwise logistic regression analysis high-resolution MRI was the only significant independent factor for SI response in CTS patients (P < 0.01). Conclusions High-resolution MRI correlates well with SI response in CTS patients and seems useful for predicting SI response. Key Points MRI may help determine appropriate care in carpal tunnel syndrome. MRI helps in therapeutic decision-making whenever steroid injection is considered. T2 signal decrease of the median nerve correlates with poor outcome. T2 signal decrease of median nerve may reflect fibrosis and amyloid deposition.