Purpose: Local steroid injection is an effective treatment modality for carpal tunnel syndrome. This study aimed to investigate the success rate of ultrasonography-guided local steroid injection and determine the prognostic value of the cross-sectional area (CSA) of the median nerve for steroid injection.

Methods: We retrospectively evaluated 40 patients with carpal tunnel syndrome whose median nerve CSA was >15 mm² (large-CSA group; n = 16) or ≤15 mm² (small-CSA group; n = 24). The CSA was measured using ultrasonography, and all the patients were treated with ultrasonography-guided corticosteroid injection. Demographic characteristics, symptoms, initial QuickDASH score, Boston Carpal Tunnel Questionnaires, and results of the nerve conduction study were assessed at baseline. Treatment success was defined in this study as the absence of symptom recurrence within the entire follow-up period.

Results: The treatment success rate was 45% (n = 18) after an average follow-up of 16 months. Overall, 11 patients (28%) underwent carpal tunnel release on an average of 11 months after steroid injection. The large-CSA group showed a significantly worse grade of electrodiagnostic testing at baseline than did the small-CSA group; however, there was no significant difference in final Boston Carpal Tunnel Questionnaires symptom score (1.7 vs 1.8, respectively) and the rate of continued treatment success at the last follow-up (42% vs 50%, respectively). The proportions of patients who required carpal tunnel decompression were 29% and 25% in the small-CSA and large-CSA groups, respectively.

Conclusions: Local steroid injection for carpal tunnel syndrome has an overall success rate of 45% after a mean follow-up of 16 months. Preinjection CSA was not associated with whether the steroid injection was considered successful. This indicates that increased median nerve CSA does not preclude the possibility of symptomatic relief after a local steroid injection.

Type of study/level of evidence: Therapeutic IV.

Keywords: Carpal tunnel syndrome; cross-sectional area; median nerve; sonography; steroid injection.