Test-retest reliability of combined sensory index

The H reflex from the abductor brevis hallucis muscle in healthy subjects

In order to evaluate the clinical applicability of a neurophysiological technique, information is required about the effect of technical and subjective factors on the measured parameters, and whether these measures are reliable. The reliability of measurement of a given parameter is inversely related to the variability shown by a set of measurements of that parameter made on the same subject under similar conditions. Reliable measures are fundamental to the clinical utility of any technique. We evaluated the reliability using the intraclass correlation coefficient (ICC), and assessed both single-point and test-retest normal limits for H-reflex parameters of abductor brevis hallucis (ABH). The H reflex from the ABH muscle was recorded in 36 of 43 subjects, but could not be elicited in 7 of 11 subjects who were >60 years of age. The Hmax latency increased as height increased, whereas Hmax amplitude and Hmax/Mmax amplitude ratio decreased as age and height increased. The Hmax latency and Hmax/Mmax amplitude ratio, but not Hmax amplitude, proved to be reliable. The usefulness of the H reflex from ABH in the evaluation of S2 radiculopathies is described.

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.