JBJS - 2026-03-24 - Journal Article
MRI Assessment of Median Nerve Size in Patients with Proximate Electrodiagnostic Studies.
Liu WC, Wung CH, Simeone FJ, Eberlin KR, Chen NC
Topics
Key Takeaway
MRI-measured median nerve CSA at the carpal tunnel inlet (cutoff 11.3 mm²) achieves only poor-to-fair diagnostic accuracy for CTS (AUC 0.67, sensitivity 74%, specificity 60%), limiting its utility as a standalone diagnostic tool.
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Summary
This study evaluated whether MRI-measured median nerve CSA at three wrist levels (DRUJ, inlet, outlet) correlates with EDX-confirmed CTS diagnosis in patients who underwent both studies within 90 days. Only inlet-level CSA differed significantly between EDX-positive and EDX-negative groups (14.4 vs. 11.1 mm², p=0.007); DRUJ and outlet measurements were non-significant. The optimal inlet cutoff of 11.3 mm² yielded an AUC of 0.67 with 74% sensitivity and 60% specificity, indicating poor-to-fair diagnostic performance.
Key Limitation
The retrospective design with only 76 wrists provides insufficient power to stratify diagnostic accuracy by EDX severity grade (mild, moderate, severe), which is the clinically relevant subgroup where imaging adjuncts would most likely be applied.
Original Abstract
BACKGROUND
Carpal tunnel syndrome (CTS) diagnosis has traditionally relied on electrodiagnosis (EDX) to confirm the diagnosis and to assess severity. Ultrasound has shown potential in measuring median nerve cross-sectional area (CSA) for CTS diagnosis, and magnetic resonance imaging (MRI) can be used for wrist soft-tissue evaluation. This study explored the correlation between CTS diagnosis and median nerve CSA measured on MRI at different wrist levels.
METHODS
A retrospective review of an electronic medical record database identified patients who underwent both wrist MRI and EDX within a 90-day interval between January 2000 and December 2022. Median nerve CSA was measured on axial T2-weighted images at 3 levels: proximal to the carpal tunnel inlet (the distal radioulnar joint [DRUJ]), the inlet, and the outlet. Continuous variables are presented as means ± standard deviations. A logistic regression model was constructed to evaluate the diagnostic accuracy of median nerve CSA, at the 3 anatomical levels, in identifying CTS. Empirical cut point estimation determined optimal cutoffs and corresponding areas under the receiver operating characteristic curve (AUCs).
RESULTS
Sixty-eight patients (76 wrists; mean age, 51.4 ± 14.2 years; male-to-female ratio, 26 to 50; 59 White patients, 8 Hispanic patients, and 1 Asian patient) were included. The mean median nerve CSA in the EDX-negative group compared with the EDX-positive group was 10.6 ± 3.4 versus 11.7 ± 4.0 mm2 (p = 0.248) at the DRUJ level, 11.1 ± 3.1 versus 14.4 ± 5.1 mm2 (p = 0.007) at the inlet level, and 9.8 ± 2.4 versus 11.0 ± 5.2 mm2 (p = 0.833) at the outlet level. The inlet CSA cutoff for CTS was 11.3 mm2 (AUC = 0.67), with a sensitivity of 74% and a specificity of 60%.
CONCLUSIONS
MRI-based measurements of median nerve CSA, particularly at the inlet level, suggest that relying solely on CSA measurements may not be an optimal diagnostic strategy for CTS in patients with equivocal clinical symptoms. Even with MRI and highly standardized measurement protocols, only poor-to-fair diagnostic accuracy was achieved. This study raises questions about the diagnosis of CTS based on CSA measurements.
LEVEL OF EVIDENCE
Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.