The value added by electrodiagnostic testing in the diagnosis of carpal tunnel syndrome

There is no clear-cut consensus on the best diagnostic criteria for carpal tunnel syndrome. The objective of this study was to compare the probability of carpal tunnel syndrome being present following electrodiagnostic testing with the probability of it being present after the diagnosis was established on the basis of a clinical evaluation alone.

The study sample included patients with any peripheral nerve diagnosis who had been referred to the electrodiagnostic laboratory of an academic health-care center. The probability of carpal tunnel syndrome before electrodiagnostic testing (pretest probability) was estimated with use of the CTS-6, a validated clinical diagnostic aid that is used to estimate the probability of carpal tunnel syndrome on the basis of the presence or absence of six clinical findings recorded as part of the history or noted on physical examination. All patients then underwent a standard electrodiagnostic assessment of the median nerve by a neurologist blinded to the result of the CTS-6 evaluation. Sensory nerve conduction velocity was used to classify the result of the electrodiagnostic testing as either positive or negative for carpal tunnel syndrome with use of two different criteria (one stringent and one lax) derived from the literature. The main outcome measure was the difference between the pretest and posttest probabilities of carpal tunnel syndrome.

One hundred and forty-three patients were studied. The pretest probability of carpal tunnel syndrome ranged between 0.10 and 0.99 (mean [and standard deviation], 0.81 +/- 0.22). Seventy-three percent of the patients had a pretest probability of at least 0.80. The average change in probability for these patients was -0.02 when the stringent electrodiagnostic criterion was used and -0.06 when the lax criterion was used. With either electrodiagnostic criterion, the majority of the large changes in probability were for patients for whom the pretest probability was < or =0.50. The probability of carpal tunnel syndrome was lowered after the electrodiagnostic testing in most of these cases.

For the majority of patients who are considered to have carpal tunnel syndrome on the basis of their history and physical examination alone, electrodiagnostic tests do not change the probability of diagnosing this condition to an extent that is clinically relevant.