When to use the combined sensory index.

A recently developed electrodiagnostic technique, the combined sensory index (CSI), has been recommended for its greater sensitivity in diagnosing carpal tunnel syndrome (CTS). The CSI requires a greater number of procedures and therefore involves greater time, cost, and patient discomfort than does conventional electrodiagnostic testing. The CSI is composed of three commonly used electrodiagnostic techniques. There is a close correlation between the components of the CSI, and in most cases, all three components of the CSI are in agreement. We performed a study to develop and validate an algorithm that could be used to identify subsets of patients with CTS in whom CSI testing is particularly useful. Subjects were consecutive outpatient veterans referred by a heterogeneous group of specialists and generalists for electrodiagnostic evaluation of paresthesias in a median distribution with nocturnal exacerbation of symptoms. The CSI served as our gold standard. Using our simple algorithm, we found that in approximately 95% of cases, it was unnecessary to perform the CSI. This management strategy improves patient comfort and reduces electrodiagnostic cost while identifying the minority of patients for whom the CSI is indicated.