Diagnosis of Cubital Tunnel Syndrome Using Ultrasound – A Retrospective Comparison to Electrophysiologic Studies
Thomas John Carroll, MD1; Alexander Chirokikh, BS1; Courtney Jones, PhD, MPH2; Eric Logigian, MD1; Constantinos Ketonis, MD, PhD2
1University of Rochester, Rochester, NY; 2University of Rochester Medical Center, Rochester, NY
Introduction: The purpose of our study is to determine the utility of ultrasound (US) in the diagnosis of cubital tunnel syndrome (CuTS) as characterized by increased cross-sectional area (CSA) of the ulnar nerve around the elbow. We hypothesize that CSA ?10 mm2 will be highly sensitive and specific for diagnosing CuTS, while also detecting some patients with early clinical symptoms CuTS with negative electrodiagnostic studies (EDX) results.
Materials & Methods: This is a retrospective study of patients presented to a large academic institution that were clinically diagnosed with CuTS and underwent both EDX and US testing. Clinical exam findings, age, gender, and duration of symptoms were recorded, as well as EDX data and CSA measurements stratified by anatomic site around the elbow. Statistical analysis of the EDX and CSA data was conducted using unpaired T-test, Chi-square, and one-way ANOVA testing.
Results: A total of 89 patients and 115 nerves were included. In this cohort, 57% of patients were female and 43% male with mean age of 58.8 ± 14.1. Mean duration of symptoms was 25.9 ± 51.4 months. Average CSA at the medial epicondyle was 14.36 ±1.01 mm2, proximal to the elbow was 9.39 ±0.71 mm2 and distal to the elbow was 8.96 ±0.84 mm2. Maximal CSA was highly correlated with disease severity as determined by EDX: mild (12.92 ± 2.1 mm2), moderate (14.78 ± 3.4 mm2), and severe (18.03 ± 2.9 mm2), p<0.001. Using a cutoff of CSA ? 10 mm2 (US+) demonstrated a sensitivity of 0.97 and specificity of 0.83 in predicting decreased motor velocity (< 50 m/s). Compared to EDX+/US+, patients with EMG-/US+ showed proportionally higher rates of ulnar sensory loss (p<0.04) with similar rate of positive Tinel, elbow tenderness, atrophy, and ulnar motor weakness. EMG+/US+ patients showed proportionally higher rates of positive Tinel sign and ulnar weakness.
Conclusion: US is a highly sensitive test used in the diagnosis of cubital tunnel syndrome that may be able to better identify patients with early stages of CuTS with negative EDX. Increased ulnar nerve CSA correlates with increased motor conduction velocity of <50 m/s, and it is most commonly the largest at the medial epicondyle. Maximum CSA is highly correlated with EMG severity score. Patients with US +/ EDX -, have proportionally higher rates of ulnar sensory loss. EMG+/US+ patients showed proportionally higher rates of positive Tinel sign and ulnar weakness.
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