Electrodiagnostic Findings Using Radial Motor Segmental Conduction Study and Inching Test in Patients with Radial Neuropathy

ABSTRACT Objective The aim of this study was to characterize the electrodiagnostic findings of radial neuropathy using motor segmental conduction study (RMSCS), and to determine the utility of subsequent inching test in precise lesion localization. Design Twenty-three patients with radial neuropathy were evaluated using RMSCS with three-point stimulation. The pathomechanism of the lesions according to the RMSCS was classified into three groups: conduction block (CB), mixed lesion (combination of CB and axonal degeneration), and axonal degeneration. Inching test was performed in patients with CB to localize the lesion site, and needle EMG identified the most proximal radial nerve-innervated muscles affected. Results Out of twenty-three cases, the RMSCS demonstrated probable partial CB in 10, mixed lesions in 2, and axonal degeneration in 10. One case could not be categorized with RMSCS alone. As determined by RMSCS and inching test, the most common cause of CB was compression, while the most common cause of axonal degeneration was iatrogenic. In the CB group, the lesion locations identified by RMSCS and inching test were consistent with needle EMG localization. Conclusion The combined RMSCS and inching test technique can precisely localize radial motor nerve injuries and provide detailed information on electrodiagnostic characteristics of radial mononeuropathy.