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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 mm2 resulted in approximately equal sensitivity and specificity, but only moderate LRs. A cutoff of <8 mm2 had satisfactory power to rule out CTS: the fitted-negative LR was 0.13. Conversely, a cutoff of ≥12 mm2 had excellent power to rule in CTS, with a fitted-positive LR of 19.9. For nerves ≥12 mm2 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.