[Study of the proximal conduction of the arms using SEP and MEP]

The proximal conduction of the upper limb has been studied with the somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) in 40 controls which provided normal data. The SEP allowed the sensory conduction study of the Erb/C7 segment with N9/N13 delay determination after the median nerve stimulation at the wrist, and after the ulnar nerve stimulation at the wrist (20 cases) or above the elbow (20 cases). The N9/N13 delay was 3.24 ms +/- 0.35 for the median nerve, 3.30 ms +/- 0.52 for the ulnar nerve after stimulation at the wrist and 3.30 ms +/- 0.40 after stimulation at the elbow. The Erb point potential amplitude after ulnar nerve stimulation at the elbow was always greater than after the median nerve stimulation at the wrist: 13.2 microV versus 8.8 microV. The MEP allowed the C6/axilla motor conduction study. The recording was performed on the adductor digiti quinti. The proximal motor conduction velocity was 74 m/s +/- 8 (mini 60). The conduction delay was then 3.02 ms +/- 0.3. A constant amplitude loss was observed between the axilla and the cervical spine; it was never greater than 30% in controls. Allthings considered both methods provided very complementary data on the proximal nerve conduction of the upper limb at the brachial plexus. The conduction delay in the brachial plexus was around 3 ms and was very similar to the distal motor and sensory latencies of the median nerve at the wrist. Motor conduction blocks of more than 30% and 1 ms increament of the conduction delay were regarded as pathological.