The predominant electrophysiologic feature of vasculitic mononeuropathy mul
tiplex is axonal loss. Electrophysiologic findings interpreted as conductio
n block have, however, also been reported to occur in neuropathy secondary
to necrotizing vasculitis. We report 3 patients with mononeuropathy multipl
ex and biopsy proven vasculitis in whom eight nerves met criteria for condu
ction block. In each circumstance, serial study demonstrated conversion of
the electrophysiologic findings to those most consistent with severe axonal
loss. "Conduction block" in vasculitic mononeuropathy multiplex is seconda
ry to focal axonal conduction failure presumably related to infarctive axon
al injury. The term conduction block should be used with caution in this di
sorder and only if serial studies demonstrate findings consistent with this
electrophysiologic diagnosis. (C) 1999 John Wiley & Sons, Inc.