Electrophysiological findings in pressure palsy of the brachial plexus.

Two patients with signs and symptoms of paralysis of the brachial plexus, caused by compression during surgery in one (case 1) and by a knapsack in the other (case 2), were examined. The characteristic electrophysiological findings were: (i) severe attenuation of amplitude of motor and sensory nerve action potentials evoked or recorded above the site of nerve injury compared to those evoked or recorded below, and (ii) slowing of motor and sensory conduction across the damaged area. Case 1 made a complete recovery clinically and electrophysiologically; EMG in case 2 suggested the presence of Wallerian degeneration. The palsies were classified as a local demyelinating block alone (case 1) or combined with axonal loss (case 2).