The present study by Graham emphasizes that although electrodiagnostic testing is the gold standard test in the evaluation of a patient with suspected carpal tunnel syndrome, it may not always add value to a diagnostic workup. Dr. Graham has argued elsewhere that "the absence of consensus on the best diagnostic criteria for [carpal tunnel] syndrome is related to a general reliance on the results of electrodiagnostic testing as a diagnostic gold standard1." This investigation identified a group of patients for whom electrodiagnostic testing does not substantively contribute to the diagnosis. Said another way, if the diagnosis was made by clinical criteria, then electrodiagnostic testing was confirmatory at best. However, insufficient focus was given to the role of electrodiagnostic testing in supporting or refuting the findings of the clinical instrument, the CTS-6, in the following areas: predicting surgical outcomes, evaluating the need for revision surgery, and managing patients with Workers' Compensation claims.
It is true that an accurate diagnosis is the first step in an evidence-based approach to carpal tunnel syndrome. The author's strict adherence to these methods is to be commended, and the rational approach to defining this syndrome is worth emulating. However, the CTS-6 has not been independently validated in the clinical setting. The fact that the study was conducted at a tertiary care center and all patients were referred for the evaluation of "any upper-extremity peripheral nerve problem" may enhance the pretest probability since the majority of nerve problems were carpal tunnel syndrome. Hence, there remains the necessity of validating this clinical instrument in the community setting. We eagerly await the results of the study "under development" that would assess a prototype instrument and point system for use by primary care physicians.
In the meantime, it is difficult to match the author's own citation of 97% specificity for the "stringent" electrodiagnostic testing diagnostic criteria and the 92% sensitivity for the "lax" criteria when considering other tests or questionnaires such as the CTS-6. The present study also identifies patients with a pretest probability between 0.60 and 0.80 for whom electrodiagnostic testing has its most valuable role. Other investigators support the conclusion that electrodiagnostic testing may be useful in cases in which the diagnosis is unclear2. Likewise, electrodiagnostic testing is quite valuable when a patient has persistent symptoms after surgery. The ability to compare a postoperative study to a preoperative study can help to determine whether or not revision surgery is necessary. The critical confirmatory role of electrodiagnostic testing in the diagnostic workup leading to revision carpal tunnel surgery has been discussed by Luria et al. and others3,4.
This investigation contrasts sharply with the experience in some regions of the United States, where up to two-thirds of workers are covered by a state Workers' Compensation, and population-based studies are possible. Storm et al. observed that in 1999, more than one-third of Medicare patients undergoing carpal tunnel release in Washington state had an "inappropriate electrodiagnostic workup before the surgery"5. Storm et al. arrived at the opposite conclusion to Dr. Graham's. They argued that policy makers should consider "mandating an appropriate electrodiagnostic test before approving carpal tunnel release." Moreover, Jarvik et al. demonstrated that electrodiagnostic testing adds value beyond its diagnostic role in carpal tunnel syndrome and serves as a prognosticator of outcomes in cases of Workers' Compensation. Specifically, median-ulnar sensory latency difference serves as a predictor of surgical benefit6. The present investigation does not indicate whether the CTS-6 would predict outcomes.
Until these issues are fully explored and answered, electrodiagnostic testing remains the most important diagnostic and prognostic tool for carpal tunnel syndrome.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.
1. Graham B. The diagnosis and treatment of carpal tunnel syndrome. BMJ. 2006;332:1463-4.
2. Jordan R, Carter T, Cummins C. A systematic review of the utility of electrodiagnostic testing in carpal tunnel syndrome. Br J Gen Pract. 2002;52:670-3.
3. Luria S, Waitayawinyu T, Trumble TE. Endoscopic revision of carpal tunnel release. Plast Reconstr Surg. 2008;121:2029-36.
4. Rigler I, Podnar S. Impact of electromyographic findings on choice of treatment and outcome. Eur J Neurol. 2007;14:783-7.
5. Storm S, Beaver SK. Giardino N, Kliot M, Franklin GM, Jarvik JG, Chan L. Compliance with electrodiagnostic guidelines for patients undergoing carpal tunnel release. Arch Phys Med Rehabil. 2005;86:8-11.
6. Jarvik JG, Comstock BA, Heagerty PJ, Haynor DR, Fulton-Kehoe D, Kliot M, Franklin GM. Magnetic resonance imaging compared with electrodiagnostic studies in patients with suspected carpal tunnel syndrome: predicting symptoms, function, and surgical benefit at 1 year. J Neurosurg. 2008;108:541-50.