Comparison of proximal and distal cross-sectional areas of the median nerve, carpal tunnel, and nerv/tunnel index in subjects with carpal tunnel syndrome

Abstract

OBJECTIVES: To provide a quantitative analysis of ultrasonographic measurements and possible pathophysiology of carpal tunnel syndrome by comparing cross-sectional areas of the median nerve, carpal tunnel, and nerve/tunnel index and the difference in ultrasonographic findings between affected and nonaffected hands and between sexes. DESIGN: Blinded comparison study. SETTING: Secondary referral and training hospital of institutional practice. PARTICIPANTS: Patients (N=51; 42 women, 9 men) with suspected carpal tunnel syndrome who underwent sonography within 1 week after the electrodiagnostic study. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Electrodiagnostic and ultrasonographic studies were conducted on both upper extremities. Cross-sectional areas of the median nerve and carpal tunnel were measured at 2 separate levels; proximal and distal cross-sectional areas of the carpal tunnel were each measured at the scaphoid-pisiform and trapezium-hamate levels, respectively. RESULTS: Comparison between normative (n=24) and abnormal hands (n=78) revealed the following: the mean proximal cross-sectional areas of the median nerve, carpal tunnel, and nerve/tunnel index of electrodiagnostically normative hands were 10.941mm(2), 192.43mm(2), and 5.635%, respectively, whereas those of abnormal hands were 13.74mm(2), 208.87mm(2), and 6.693%, respectively, showing statistically significant differences for all (P<.05). Distal measurements of the cross-sectional area of the median nerve, carpal tunnel, and nerve/tunnel index were 10.088mm(2), 150.4mm(2), and 6.762%, respectively, in normative hands, and 11.178mm(2), 149.6mm(2), and 7.493%, respectively, in abnormal hands, showing no statistically significant differences (P>.05). In women, proximal cross-sectional areas of the median nerve and nerve/tunnel index of abnormal hands showed statistically significant differences, but no ultrasonographic measurement with a statistically significant difference was observed in men. CONCLUSIONS: Compared with nonaffected hands, the proximal cross-sectional areas of the median nerve and carpal tunnel were greater, but the distal ultrasonographic measurements were not in affected hands. Ultrasonographic findings of carpal tunnel syndrome were different according to sex.