Sensitivity, specificity, and variability of nerve conduction velocity measurements in carpal tunnel syndrome

OBJECTIVE: To explore the diagnostic values of 8 commonly used electrodiagnostic techniques for measuring median nerve conduction velocity (NCV) in carpal tunnel syndrome (CTS). DESIGN: Sensitivity and specificity analyses. SETTING: A hospital-based electrodiagnostic laboratory. PARTICIPANTS: Forty-four normal hands and 136 symptomatic hands. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: (1) Long-segment studies: antidromic wrist-to-digit sensory NCV without subtraction, (2) short-segment studies: transcarpal palm-to-wrist mixed NCV without subtraction, and (3) 2 segment studies: antidromic transcarpal sensory NCV with subtraction (differential calculation from wrist-to-digit and palm-to-digit segments). Both onset and peak latency values were obtained for calculating the NCV. Sensitivity, specificity, and coefficient of variance were calculated for each NCV study. RESULTS: The short-segment, onset latency-based transcarpal mixed NCV yielded the highest sensitivity (75%). CONCLUSIONS: Results from measurement of a single, short-nerve segment tended to be superior to results obtained by either long-segment studies or differential subtraction between 2 segments of the same nerve in the electrodiagnosis of CTS. Explanations for our results are offered from both electrophysiologic and statistical perspectives.