13. Comparison of digits 2 and 3 sensory studies in patients with carpal tunnel syndrome

Abstract

Introduction According to AANEM guidelines, an initial step in the electrodiagnostic study for carpal tunnel syndrome (CTS) is the recording of median sensory response across the wrist. Although any median nerve innervated digit can be studied, digit 2 is most common. Objective The current prospective study was undertaken to determine differences between median nerve sensory parameters following stimulation of digit 2 and 3 in patients presenting with clinical CTS. Methods We prospectively studied 211 wrists in 158 patients with clinically definite CTS defined as nocturnal and/or activity-related sensory symptoms, sensory deficits in the median nerve distribution, or weakness and/or atrophy of median-innervated thenar muscles. Electrophysiological studies were conducted using standard techniques based on the AANEM practice parameters. Specifically, orthodromic sensory studies were performed following stimulation of both digit 2 and 3. Comparison sensory studies with the radial nerve were performed with stimulation at digit 1. Median motor studies were also performed. A cohort of normal patients were also recruited and studied. Results Sensory conduction velocity (SCV) following digit 3 stimulation (32.3 ± 14.5m/s) was significantly slower ( P 0.001) when compared to digit 2 (35.1 ± 14.1m/s) in all severity groups, although the difference was most pronounced in patients with mild compared to those with severe CTS ( p =0.005). 5% of the total cohort had normal digit 2 SCV, but abnormal digit 3 SCV. In our cohort of normal wrists, there was no significant difference between digits 2 and 3 SCV and sensory amplitude. Conclusion Orthodromic median nerve sensory studies following digit 3 stimulation are significantly more abnormal compared to digit 2 stimulation in patients with CTS, and may be more sensitive for the diagnosis of CTS, particularly in mild cases.