Prospective Evaluation of Sensitivity and Specificity of CTS-6 for Diagnosis of Carpal Tunnel Syndrome
Brian H. Gander, MD; John R. Fowler, MD
Orthopaedic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA
Introduction: Carpal tunnel syndrome (CTS) is a compressive neuropathy and accounts for 90% of all cases of compressive neuropathy. Current AAOS Clinical Practice Guidelines give a Grade of Recommendation B to the use of electrodiagnostic studies in the setting of positive clinical or proactive. Graham et. al published a clinical diagnostic criteria for CTS where he found six clinical criteria that were statistically significant in the probability of diagnosing CTS. Subsequently, Graham demonstrated that electrodiagnostic studies do not change the likelihood of diagnosing CTS secondary to the high probability that can be estimated with CTS-6. Our prospective study aims define the diagnostic validity of CTS-6 when compared to the reference standard of electrodiagnostic testing.
Methods: Eighty-five consecutive patients over a three month period whom were referred for electrodiagnostic studies were prospectively enrolled into the study. A blinded, certified electrodiagnostic technician performed all electrodiagnostic testing. A distal motor latency > 4.2 ms or distal sensory latency > 3.2 ms was considered positive. A hand fellow, not involved in the electrodiagnostic examinations and trained to independently examine patients calculated the CTS-6 score. A score of 12 or greater was considered a positive diagnosis of CTS and less than 12 was negative. Sensitivity and specificity were calculated using electrodiagnostic testing as the reference standard.
Results: Fifty five of 85 patients tested positive for CTS with EMG/NCS and of those 49 tested positive for CTS using CTS-6. Thirty patients found not to have CTS based upon electrodiagnostic studies and 24 of those tested negative using CTS-6. The calculated sensitivity and specificity of CTS-6 was found to be 0.89 and 0.80 respectively.
Discussion: Current AAOS Guidelines give a strong recommendation to proceeding with electrodiagnostic studies in the setting of clinical finding as a confirmatory test. Graham devised a new clinical diagnostic test that challenges the routine of electrodiagnostic studies when diagnosing CTS. No prospective studies have evaluated the diagnostic validity of CTS-6 when compared to electrodiagnostic studies as the reference standard. In our study we found CTS-6 to have similar sensitivities and specificities to other confirmatory imaging tests. An accuracy of 86% for CTS-6 is respectable, but likely not high enough to suggest that CTS-6 can replace EMG/NCS. The relatively low specificity of 80% means that CTS-6 does not function as well as EMG/NCS as a good confirmatory test. The high sensitivity of 89% means that it is a relatively strong screening test.
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