Correlation Nerve Conduction Studies with Findings of the Ultrasound of the Median Nerve in Patients with Carpal Tunnel Syndrome

Abstract

Background: Ultrasonography is a diagnostic resource that serves as a complement in the evaluation of patients with carpal tunnel syndrome. The correlation of ultrasonography findings with nerve conduction studies can serve to classify new phenotypes and to evaluate therapeutic responses. Objectives: To determine the diagnostic sensitivity of ultrasound, the correlation between the diameter of the nerve (CSA) against the motor and sensitive latencies, and the capacity to differentiate the mild, moderate and severe degrees of the electrophysiological classification of carpal tunnel syndrome. Methods: A cross-sectional study with prospective data collection was carried out. An ultrasonography system with a 15 MHz transducer was used. Nerve conduction studies of the median nerve were performed with conventional techniques. Data from the most symptomatic hand were used. Determination of the correlations of nerve diameter with motor and sensitive latencies of the median nerve was performed in four age groups: <40(n=11), 40-54 (n=47), 55-70 (n=42) y >70(n=27). Results : A total of 127 patients were evaluated (average age = 58.2 years: minimum = 26; maximum = 85; SD = 13.4); 109 (85.8%) were female patients. According to the electrophysiological classification, 40 (31.5%) were mild ; 60 (47.2%) were moderate ; and 27 (21.3%) were severe . Significant differences in the area of the median nerve were found between the electrophysiological types (mild, moderate and severe; p = 0.000). The diagnostic sensitivity of ultrasonography differed for each age group. In general, the diagnostic sensitivity was high in patients with severe cases and low for mild cases. The capacity for ultrasonography to classify the degrees of electrophysiological severity was different for each age group. For patients above 70 years and in the age group of 40 to 54 years, the CSA did not differentiate the electrophysiologically moderate cases from the severe ones. Conclusions: There is a well-defined and significant correlation between nerve conduction studies and median nerve diameter in patients with Carpal Tunnel Syndrome. However, it shows that the exclusive use of the ultrasonographic measurement of the cross-sectional area through the inlet of the carpal tunnel would not be enough to confirm or rule out an entrapment of the median nerve through the carpal tunnel, nor to predict in every case their electrophysiological severity.