[Diagnostic value of somatosensory evoked potentials (SEP) in lesions of the brachial plexus (author's transl)].

Simultaneous recording of SEP from the contralateral scalp, the lower neck (C 7) and Erb's point following median or ulnar nerve stimulation may be helpful in the localisation of lesions of the brachial plexus and associated spinal roots. In lesions proximal to the dorsal root ganglia, the potential recorded from Erb's point (EP), as well as the first component of the neck-SEP ("NSEP 1", "N 9") are normal, whereas the following components of the cervical response ("NSEP 2 + 3", "N 11 + N 13") are reduced or absent, depending on the severity of the functional impairment (Fig. 1). In lesions distal to the ganglia the EP-potential shows a significant reduction in amplitude as compared to the normal side. The neck- and scale-SEP are less attenuated or even normal in this condition, because of the phenomenon of synaptic amplification (Fig. 2). Combined lesions of the brachial plexus and cervical roots, which especially occur in traumatic injuries are characterized by an attenuation of the EP-potential and a relatively larger attenuation or an absence of the neck-SEP (N 13) (Fig. 3). SEP examination may therefore be valuable in estimating the degree of involvement distal and proximal to the dorsal root ganglia.