To diagnose brachial plexopathies is often challenging for neurologists. The complexity in anatomy of brachial plexus may preclude easy understanding of the anatomic localization, and the clinical features of plexopathy may mimic myelopathies, radiculopathies or neuropathies, which are more common disorders. Furthermore, imaging studies such as MRI or CT have limited utility for localization of disorders. In such situations, electrodiagnostic tests are most useful for determining localization of plexopathies. Nerve conduction studies (NCSs) and needle electromyography will contribute to localization in the brachial plexus and to the differential diagnosis. Especially, the sensory nerve conduction studies (SCSs) are promising, because sensory nerve action potential (SNAP) amplitude will decrease in plexopathies due to Wallerian degeneration of the postganglionic sensory fibers. Another advantage of SCS is the higher sensitivity in a chronic disease process, in which the compound muscle action potential might be preserved due to reinnervation. For the electrodiagnosis using SCSs, a criterion to consider an interside difference exceeding 50% as abnormal has been widely employed, which has not been actually verified. We have investigated the validity of this hypothesis and established the control values. Four cases of plexopathies have been also presented.
