Strategies for analyzing nerve conduction data: superiority of a summary index over single tests.
We compared three strategies for diagnosing carpal tunnel syndrome: using a single test; requiring one, two, or three of three tests to be abnormal; or utilizing a single summary variable incorporating data from three tests. Sixty-five hands of subjects without clinical carpal tunnel syndrome (CTS) were compared with 66 hands with clinical CTS. Three latency differences were measured: median-ulnar (8 cm) midpalmar orthodromic (palmdiff); median-ulnar ring finger (14 cm) antidromic (ringdiff); and median-radial thumb (10 cm) antidromic (thumbdiff). The combined sensory index (CSI) was the sum of these three differences. Sensitivity for the tests was palmdiff 69.7%, ringdiff 74.2%, thumbdiff 75.8%, and CSI 83.1%. Specificity was 95.4-96.9%. Requiring one, two, or three of three tests to be abnormal yielded sensitivities of 84.8%, 74.2%, or 56.1%, respectively, but specificities of 92.3%, 98.5%, and 100%, respectively. We conclude that a combined index improves diagnostic classification over use of single test results.
Rehabilitation Medicine, Harborview Medical Center, Seattle, Washington 98104, USA.
L R
LR
Robinson
P J
PJ
Micklesen
L
L
Wang
D002349:Carpal Tunnel Syndrome / Q000175:diagnosis*; D016002:Discriminant Analysis; D006225:Hand / Q000294:innervation; D006801:Humans; D009431:Neural Conduction / Q000502:physiology*; D009482:Neurophysiology / Q000379:methods*; D011446:Prospective Studies; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D012680:Sensitivity and Specificity