Enhancing diagnostic accuracy using a side-to-side cross-sectional area ratio for the diagnosis of unilateral ulnar mononeuropathy at the elbow

Introduction Neuromuscular ultrasonography (NMUS) is a valuable adjunct to electrodiagnostic testing for the diagnosis of entrapment neuropathy. The aim of this study was to determine whether diagnostic accuracy of NMUS could be enhanced in patients with unilateral ulnar mononeuropathy at the elbow (UNE) by utilizing side-to-side ulnar nerve cross-sectional area (CSA) ratios. Methods Retrospective case-control analysis of unilateral UNE cases identified cutoff values for elbow segment ulnar nerve maximum CSA (MCSA) of the symptomatic/asymptomatic limb (M ratio), as well as side-to-side ratios comparing MCSA with ipsilateral CSA at the Guyon canal (E/G), middle forearm (E/F), and middle humerus (E/H). Diagnostic accuracy values were calculated. Results The optimal M-ratio cut-off was 1.22 (sensitivity, 92.9%; specificity, 97.8%; accuracy, 95.4%). Optimal cutoffs for inter-E/G, -E/F, and -E/H ratios were 1.07 (sensitivity, 98%; specificity, 78%; accuracy, 87.7%), 1.11 (sensitivity, 95%; specificity, 80%; accuracy, 87.2%), and 1.18 (sensitivity, 95%; specificity, 93%; accuracy, 94%), respectively. Discussion The M ratio and inter-E/H ratio exhibited high diagnostic accuracy for unilateral UNE. Prospective studies are needed to compare the accuracy of the new measures with a single MCSA measurement.

Automated summary

NMUS is a valuable adjunct for diagnosing entrapment neuropathy. Utilizing side-to-side ratios can enhance diagnostic accuracy for unilateral UNE. The M ratio and inter-E/H ratio show high diagnostic accuracy and may be useful in prospective studies for comparison with single MCSA measurement.