Test-retest reliability of combined sensory index: Implications for diagnosing carpal tunnel syndrome

When compared to single nerve conduction tests, the combined sensory index (CSI) has been shown previously to have superior sensitivity and specificit y for diagnosing carpal tunnel syndrome. The CSI is the sum of (1) median-u lnar ring finger antidromic latency difference at 14 cm (ring-diff); (2) me dian-radial thumb antidromic latency difference at 10 cm (thumb-diff); and (3) median-ulnar midpalmar orthodromic latency difference at 8 cm (palm-dif f). To evaluate the reliability of single nerve conduction tests (ring-diff , thumb-diff, and palm-diff) vs. a combined summary variable (CSI), we cond ucted a prospective study during which the same investigator performed test and retest sessions on one hand of 32 subjects. Results showed that the CS I had the highest test-retest reliability (Spearman rho = 0.95), when compa red with ring-diff, thumb-diff, and palm-diff (Spearman rho = 0.67, 0.75, a nd 0.74, respectively). Therefore, we propose the use of the CSI as not onl y an accurate but also a reliable method for diagnosing carpal tunnel syndr ome. (C) 2000 John Wiley & Sons, Inc.