Somatosensory cerebral evoked potentials in diagnosing brachial plexus injuries.

Seven patients, 5 months up to 7 years after closed injury of the brachial plexus, were stimulated in the wrist, elbow and axilla of the extremity affected in order to invistigate average somatosensory cerebral evoked potentials (SCEP). Avulsion of most of the roots C5-Thl from the spinal cord could be objectively proved. All available clinical, contrast X-ray, and electrophysiological methods were used as well as surgical approach in the supraclavicular region or laminectomy. Sensation was objectivized by the galvanic skin reflex. Sensory nerve action potentials (NAP) were registered from the ulnar, median, radial nerves. Absence of SCEP in normal NAP helped to localize injury at the preganglionic dorsal root level. Absence of both SCEP and NAP, as seen in one case only, was of no use in the localization. Reduced SCEPs were found in most cases (with or without NAP), with prolonged latency. SCEP can be induced by even a small part of the preserved dorsal roots, e.g. part of a single one, as actually found. The presence of reduced SCEP then does not rule out avulsion of other spinal roots. SCEP from the axilla and upper arm medial side can be conducted--not along the plexus root pathway, but along the intercostobrachia nerve (Th2-3), which normally supplies that skin region.