Sonographic examination of the median nerve has been suggested as a useful alternative to electrophysiologic study in the diagnosis of carpal tunnel syndrome. To determine its usefulness and the best diagnostic criterion, sonograms of patients with the disease were compared with sonograms of healthy subjects in a case–control study.
Patients with carpal tunnel syndrome and asymptomatic controls who were matched for age and sex were enrolled and underwent sonography of the wrists. Eight separate sonographic criteria were analyzed in each wrist. Data from the patient group and the control group were compared to establish optimal diagnostic criteria for carpal tunnel syndrome, using receiver operating characteristic analytic techniques.
Thirty-five patients with carpal tunnel syndrome and 35 asymptomatic controls were examined. Increased cross-sectional area of the median nerve was found to be the most predictive measure of carpal tunnel syndrome, proximal to the tunnel inlet, at the tunnel inlet, and at the tunnel outlet, with significant differences between patients and controls. Using a receiver operating characteristic curve, a cut-off value >0.098 cm2 at the tunnel inlet provided a diagnostic sensitivity of 89% and a specificity of 83%.
Sonographic measurement of the median nerve cross-sectional area is both sensitive and specific for the diagnosis of carpal tunnel syndrome.