Every major league baseball pitcher, most minor league pitchers, but o
nly few amateur pitchers that we have studied have had reduced sensory
nerve action potentials in the throwing arm. We present 6 clinical ca
ses which demonstrate the spectrum of ''pitcher's arm.'' These cases s
uggest that the phenomenon is a pathologic process, probably an exampl
e of a repetitive use syndrome affecting the brachial plexus. Although
it does not appear to impact performance, it has clear implications f
or the interpretation of electrodiagnostic studies in symptomatic pitc
hers. (C) 1996 John Wiley & Sons, Inc.