Diagnostic value of sonography in patients with suspected carpal tunnel syndrome: a prospective study.
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 > or =12 mm(2) had excellent power to rule in CTS, with a fitted-positive LR of 19.9. For nerves > or =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%.


CONCLUSIONS
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.
Ziswiler
Hans-Rudolf
HR
Department of Social and Preventive Medicine, University of Berne, Finkenhubelweg 11, Berne 3012, Switzerland.
Reichenbach
Stephan
S
Vögelin
Esther
E
Bachmann
Lucas M
LM
Villiger
Peter M
PM
Jüni
Peter
P
D000328:Adult; D000368:Aged; D002349:Carpal Tunnel Syndrome / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D009431:Neural Conduction; D011336:Probability; D011446:Prospective Studies; D012372:ROC Curve; D012680:Sensitivity and Specificity; D014463:Ultrasonography / Q000592:standards