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Changes in nerve conduction velocity across the elbow due to experimental error
Mark E Landau1, Myrna I Diaz, Kristen C Barner
1Department of Neurology, Walter Reed Army Medical Center, 6900 Georgia Avenue, Washington, DC 20307, USA. mark.landau@na.amedd.army.edu
Muscle & Nerve
|November 27, 2002
Summary
Measurement errors in nerve conduction velocity (NCV) calculations can lead to inaccurate diagnoses of ulnar nerve mononeuropathy at the elbow (UNE). Errors alone can account for diagnostic criteria discrepancies, questioning NCV
Area of Science:
- Neurology
- Neurophysiology
- Clinical Electrophysiology
Background:
- Ulnar nerve mononeuropathy at the elbow (UNE) diagnosis often relies on a >10 m/s decrease in across-elbow nerve conduction velocity (NCV) compared to the forearm segment.
- Nerve conduction velocity calculations are susceptible to inherent errors in distance and latency measurements.
Purpose of the Study:
- To quantify the experimental error in NCV calculations due to measurement inaccuracies.
- To assess the impact of these errors on the diagnostic criterion for UNE.
Main Methods:
- Twenty electromyographers recorded ulnar compound muscle action potential latencies.
- Forearm and across-elbow distances along the ulnar nerve were measured.
- Experimental error in NCV was calculated using established equations.
Main Results:
- Mean forearm segment distance was 212.5 ± 2.1 mm; mean elbow segment distance was 86.7 ± 4.2 mm.
- Measurement error alone can result in a 14 m/s difference for an NCV of 55 m/s.
- Significant interobserver variability exists in elbow segment distance measurements.
Conclusions:
- Measurement errors, particularly in distance, can significantly impact NCV calculations.
- The across-elbow NCV segment's value as a sole diagnostic criterion for UNE is questionable due to measurement variability.