Mixed nerve potentials in brachial plexopathy

We studied the Erbʹs point potential with supramaximal stimulation of the median nerve in 14 consecutive patients with clinical and electrophysiological evidence of unilateral brachial plexopathy and in normal controls. Both arms were studied in each individual. In each patient, the ratio of amplitude of recorded Erbʹs point potential from the affected arm to the normal arm was calculated. In controls the side with a recorded potential of a lower amplitude was used as the numerator to calculate a similar ratio. Eleven out of 14 patients had a Erbʹs point amplitude ratio less than that of controls. This method is a simple and useful adjunct in the electrophysiological assessment of brachial plexopathy.