Objective: To determine the diagnostic value of high-resolution sonography in ulnar neuropathy at the elbow (UNE).

Methods: Sonographic ulnar nerve diameter measurement was compared at three levels around the medial epicondyle with a criterion standard including clinical and electrophysiologic characteristics in a cohort of 123 patients presenting with clinical signs of UNE. UNE or probable UNE was diagnosed in 84 patients and a different condition in 39 patient controls. Reference values were obtained in 56 healthy volunteers.

Results: One hundred thirty-six affected arms were studied in 123 patients (UNE in 82, probable UNE in 9, and a different condition in 45 affected arms). Patients with UNE had a larger ulnar nerve diameter than patient controls (p < 0.0001). The sensitivity of sonography was 80%, specificity 91%, positive likelihood ratio 9, and negative likelihood ratio 0.2. The highest diagnostic yield was found in patients in whom electrodiagnostic studies showed signs of ulnar neuropathy but could not localize the lesion (17/20 cases, 86%) and in patients who had motor conduction velocity slowing across the elbow without conduction block (32/37 cases, 86%).

Conclusions: High-resolution sonography is an accurate and easily applied test for the diagnosis of UNE. The authors recommend its use in addition to electrodiagnostic studies because it improves the reliability of the diagnosis of UNE.