Ultrasonography (US) has shown increased cross-sectional area of the median nerve in carpal tunnel syndrome (CTS). Knowledge of the normal distribution of the areas is a prerequisite to evaluate pathology. Presently, the distribution of cross-sectional areas of the median nerve was explored in patients with rheumatoid arthritis (RA).
The median nerves of patients with RA having no symptoms or signs of CTS were examined with bilateral US at the entrance of the carpal tunnel.
A total of 154 patients with RA were included. The median nerve was divided in 11.7% of the hands. The mean (SD) cross-sectional areas of the undivided median nerves were not significantly different on either sides (8.3 (1.5) mm(2) on the right side and 8.3 (1.4) mm(2) on the left side). The areas of the examined 308 median nerves ranged from 5.0 to 12.8 mm(2), with the 97.5 centile being 11.1 mm(2). Areas >10.0 mm(2) were found in 10% of the patients.
The mean cross-sectional areas of the median nerve in patients with RA were similar to those reported in healthy controls. However, 10% of the patients had values that overlap with areas commonly reported in patients with mild idiopathic CTS.