Sonographic Grading of Carpal Tunnel Syndrome
Jesse D Kaplan, MD, University of California, Irvine, Orange, CA and John Fowler, MD, Orthopaedic Surgery and Sports Medicine, University of Pittsburgh, Pittsburgh, PA
Carpal tunnel syndrome is the most common compression neuropathy with over 500,000 carpal tunnel releases performed annually in the United States. Currently there is no consensus of how to objectively diagnose carpal tunnel syndrome. Ultrasound measurement of the cross-sectional area of the median nerve at the carpal tunnel inlet has been shown to be a cost effective and efficient technique with comparable sensitivity and specificity to nerve conduction studies. One concern is there are not established cutoff values to stratify the severity of compression. Therefore, the purpose of this study is to define the median nerve cross-sectional areas that correlate with increasingly severe carpal tunnel syndrome.
Materials and Methods:
Patients with carpal tunnel symptoms were prospectively enrolled and assembled in an institutional database. Information collected included demographic data, CTS-6 scores, ultrasound measurements and nerve conduction studies. Ultrasound measurements of the median nerve cross-sectional area were obtained at the level of the carpal tunnel inlet. A CTS-6 score of greater than 12 was used for carpal tunnel syndrome diagnosis. Severity was graded based on a positive CTS-6 score and secondarily by nerve conduction studies. Stepwise analysis with area under the curve and the youden index were used to define median nerve cross-sectional area cutoff values correlating to different levels of severity.
Three hundred and eight patients were included in the final analysis. Patients with CTS-6 scores of zero and normal electrodiagnostic studies had a mean median nerve cross-sectional area of 8.13 mm2. Patients with mild carpal tunnel syndrome had a mean cross-sectional area of 10.29 mm2 while those with moderate and severe disease were 11.88 mm2 and 14.23 mm2 respectively. A cutoff value of 10 mm2 for mild severity had 85.5% sensitivity and 73.0% specificity. For moderate severity, a cutoff value of 11 mm2 had 85.4% sensitivity and 65.8% specificity. Lastly for severe carpal tunnel syndrome, a cutoff value of 12 mm2 had 69.2% sensitivity and 65.7% specificity.
Ultrasound measurement of the cross-sectional area of median nerve in conjunction with clinical evaluation can be used to confirm and grade carpal tunnel syndrome. Those patients with clinically evident carpal tunnel syndrome and enlarged median nerve cross-sectional area on ultrasound can be counseled and treated based on increasingly severe disease.
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