Molecular and Clinical Elucidation of the Mechanism of Action of Steroids in Idiopathic Carpal Tunnel Syndrome.

Background Carpal tunnel steroid injection is a nonoperative intervention for the treatment for idiopathic carpal tunnel syndrome (CTS). The antifibrotic, anti-inflammatory, and antiedematous properties of steroids account for their therapeutic effects in the context of CTS; however, their relative contribution has not been clarified. Methods Fibroblasts from subsynovial connective tissues (SSCT) were intraoperatively collected from patients with idiopathic CTS and were incubated with or without the steroid triamcinolone acetonide (TA) for 1, 3, and 7 days; the expression of fibrosis-related genes and inflammatory cytokines was evaluated using quantitative reverse transcription-polymerase chain reaction. A clinical prospective study was conducted with patients who received carpal tunnel TA injections. We performed clinical and electrophysiological evaluations before and 1, 3, and 5 months after TA injection; and we compared the median nerve, flexor tendon, and SSCT areas and the median nerve flattening ratio before and 1 month after TA injection using 3-T magnetic resonance imaging (MRI). Results TA induced downregulation of the fibrosis-related genes Col1A1 (collagen type I alpha 1 chain), Col1A2, and Col3A1 but not the inflammation-related genes. The nerve flattening ratio did not change after TA injection according to the MRI-based observation of the median nerve, flexor tendon, and SSCT areas. Conclusions The therapeutic effects of injected TA are apparently mediated by its antifibrotic rather than its anti-inflammatory and antiedematous properties. TA probably alters the properties but not the morphology of SSCT. Level of evidence Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.