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Probability of carpal tunnel syndrome diagnosis by clinical evaluation changes little with electrodiagnostic testing, data indicate

Thursday, December 18 2008 | Comments

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What's This? After a clinical diagnosis of carpal tunnel syndrome (CTS) is made with the CTS-6 aid, conducting electrodiagnostic testing provides minimal diagnostic value to the health care professional, according to a recent study.

The prospective investigation was conducted to compare the probability of a CTS diagnosis when determined by clinical evaluation or by electrodiagnostic testing.

A total of 143 patients with any upper-extremity peripheral nerve problem first underwent an assessment with the CTS-6, a validated tool that estimated the probability of CTS based on the presence or absence of 6 clinical findings (pretest probability). A blinded technician and neurologist then conducted an electrodiagnostic study, with sensory nerve conduction velocity being measured over an 8-cm segment from the proximal edge of the CT to the middle finger. Results from the electrodiagnostic assessment were classified as positive or negative according to CTS definitions that were either stringent (sensory latency, >=2.27 msec) or lax (sensory latency, >2.0 msec), yielding the post-test probability.

The data showed that the pretest probability of CTS ranged from 0.10 to 0.99 (mean, 0.81). The absolute change in probability in either direction was relatively small on the electrodiagnostic test (with the stringent definition, 0.13; with the lax definition, 0.17).

The CTS-6 and the electrodiagnostic test had a correlation of 0.91 when the stringent definition was used and 0.83 when the lax definition was employed.

The results further showed that 73% of patients had a substantial pretest probability of >=0.80; their average probability post-test changed by -0.02 with the stringent criterion and -0.06 with the lax criterion. Since the probability of the condition was already high by clinical diagnosis in most cases, the researchers explained, the second test's ability to increase the probability was limited.
 
Large changes in probability were mostly evident in patients who had a pretest probability of approximately <=0.50. In these cases, the post-test probability was below the pretest probability in 81% and 96% of patients when the lax and stringent definitions were used, respectively.

"These findings suggest that the value of electrodiagnostic testing in diagnosing carpal tunnel syndrome is probably much smaller than would be suggested by its current status in most settings in which carpal tunnel syndrome is diagnosed and treated," the study authors wrote. "Decisions regarding treatment and prognosis can likely be safely made on the basis of a clinical assessment alone, although there may be some instances in which a small increase or decrease in probability resulting from the outcome of electrodiagnostic testing may influence a clinical decision."

They added that electrodiagnostic testing seems to be most valuable in patients with a pretest probability of between approximately 0.60 and 0.80. (Graham B, et al. J Bone Joint Surg Am 2008;90:2587-2593.)

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