Altered supernormality in multiple sclerosis peripheral nerve.

Supernormality is a regular part of the recovery cycle of nerve. Supernormality was expressed in terms of amplitude, and in 20 control subjects the mean (S2 conditioned/S2 unconditioned) ratio of the median sensory nerve action potential amplitude recorded at the elbow measured 285 +/- 174 (range 119 to 783). A supramaximal conditioning shock was delivered 6 msec in advance of the test pulse. Seventeen (42.5%) of 40 patients with multiple sclerosis (MS) failed to demonstrate supernormality, the (S2 conditioned/S2 unconditioned) ratio being less than 100. This abnormality probably reflects a delay in recovery cycle and is additional evidence implicating peripheral nervous system involvement in multiple sclerosis.