Gray-Scale and Power Doppler Ultrasound Findings Predictive of Cubital Tunnel Syndrome Severity

Background: The use of ultrasound in the diagnosis of cubital tunnel syndrome (CuTS) is an attractive alternative to electrodiagnostic (EDX) studies, but its utility is binary with poor severity correlation. We hypothesize that increasing ulnar nerve cross-sectional area (CSA) and power Doppler measurement of intraneural vascularity may predict the extent of disease. Methods: We identified 20 elbows from patients with a history of CuTS and 20 elbows in 10 asymptomatic controls. Electrodiagnosis was performed for symptomatic patients. Gray-scale ultrasound and power Doppler ultrasound were performed to measure CSA and intraneural vascularity in all participants. Functional measures, Boston Carpal Tunnel Questionnaire (BCTQ), and Patient-Reported Outcomes Measurement Information System surveys were also completed. Results: A strong positive correlation was found between CSA and motor nerve conduction velocity (MNCV) decrease between elbow and forearm, which increased when BCTQ >2 was used as a screening criterion. Increased CSA also demonstrated a high positive predictive value (PPV) in predicting MNCV changes, but poor ability to predict axonal loss. In contrast, power Doppler ultrasound demonstrated 100% PPV and 94% negative predictive value (NPV) in predicting severe CuTS (defined as compound motor action potential [CMAP] amplitude <6 mV and electromyography [EMG] findings). Conclusions: Cross-sectional area is a sensitive method for identifying changes in MNCV and amplitude but does not stratify disease severity, as defined by diminished CMAP amplitude and/or evidence of denervation on EMG. The presence of increased intraneural vascularity is relatively sensitive but highly specific for axonal loss. The combination of nerve CSA, BCTQ screening, and power Doppler ultrasound may provide an alternative means for CuTS assessment.