Diagnostic value of sonography in patients with suspected carpal tunnel syndrome: A prospective study

Abstract

Objective: To determine the diagnostic value of sonography in patients with suspected carpal tunnel syndrome (CTS). Methods: We conducted a prospective study of 110 wrists in 74 consecutive patients with suspected CTS who had been referred to a tertiary care center. We determined the largest cross‐sectional area of the median nerve at the carpal tunnel. Because of the lack of a universally accepted reference standard, we first examined the association of sonography with nerve conduction. Then, we compared sonography with a reference standard based on the combination of nerve conduction studies and signs and symptoms. Sonography and reference standard tests were performed independently and interpreted under blinded conditions. Based on a fitted receiver operating characteristic curve, we estimated likelihood ratios (LRs) and posttest probabilities for different cutoffs. Results: There was a high concordance between sonography and nerve conduction. Based on the combined reference standard, a cutoff of 10 mm 2 resulted in approximately equal sensitivity and specificity, but only moderate LRs. A cutoff of <8 mm 2 had satisfactory power to rule out CTS: the fitted‐negative LR was 0.13. Conversely, a cutoff of ≥12 mm 2 had excellent power to rule in CTS, with a fitted‐positive LR of 19.9. For nerves ≥12 mm 2 and a pretest probability of 70% expected in patients with suspected CTS in tertiary care, we found a posttest probability of CTS of 98%. Conclusion: Depending on setting and purpose, different cutoff values for the largest cross‐sectional area may be used to accurately rule in or rule out CTS. Using sonography as a first‐line test may cost‐effectively reduce the number of nerve conduction studies in patients with suspected CTS. A large‐scale, randomized controlled trial is required to determine the effects of sonography on clinical outcomes, the number of nerve conduction studies performed, and the total cost.