Ultrasonography Findings in Severe Carpal Tunnel Syndrome
Gideon Nkrumah, OD; University of Pittsburgh, Pittsburgh, PA; John R. Fowler, MD; Department of Orthopaedic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA
Background: Nerve conduction studies (NCS) have the advantages of supplying objective evidence of nerve compression and the ability to “grade” the severity based on the degree of slowing. Increasing severity of CTS as graded by NCS has been demonstrated to predict the speed and completeness of recovery after carpal tunnel release.1 While ultrasound (US) measurement of the cross-sectional area (CSA) of the median nerve at the wrist has been demonstrated to have similar diagnostic accuracy to NCS in specific clinical scenarios,2,3 it is unclear if US can be used to “grade” CTS severity in a similar manner to NCS.
Purpose: The purpose of this study is to compare the CSA of the median nerve in patients with “severe” CTS on NCS to patients with “non-severe” CTS on NCS. The null hypothesis is that there is no difference in CSA between these two groups.
Methods: Patients with clinical signs and symptoms of CTS were prospectively enrolled in the study. Patients with prior carpal tunnel release, history of cervical radiculopathy, polyneuropathy, and diabetes were excluded. The senior author measured the cross-sectional area (CSA) of the median nerve and the patient was then referred to a certified electrodiagnostician who performed EMG/NCS according to the standards of the AANEM. The Boston Carpal Tunnel Questionnaire (BCTQ) and CTS-6 diagnostic tool. were completed for each patient. Severe CTS was defined based on “no response” for either the distal motor latency (DML) and/or distal sensory latency (DSL) on NCS. CSA of the severe and non-severe group were analyzed together with BCTQ and CTS-6 scores.
Results: A total of 274 wrists were enrolled in the study. The mean CSA in the non-severe group was 10.0 mm2, compared to 12.7 mm2 in the severe group, P =0.05. The mean FSS in the non-severe group was 2.15, compared to 2.50 in the severe group, P =0.05. The mean SSS in the non-severe group was 2.67, compared to 3.06 in the severe group, P =0.05. The mean CTS-6 in the non-severe group was 12.4, compared to 15.9 in the severe group, P =0.05. Receiver Operator Curves (ROC) showed CSA was the most accurate variable to predict severe CTS.
Conclusions: Patients with severe CTS using NCS criteria have an elevated median nerve CSA compared to patients with non-severe CTS using NCS criteria. US was a better predictor of severity (based on NCS) than CTS-6 and BCTQ.
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