Criteria for early detection of conduction block in multifocal motor neuropathy (MMN): a study based on control populations and follow-up of MMN patients |
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Authors: | Alberto Cappellari Eduardo Nobile-Orazio Nicoletta Meucci Giulia Levi Minzi Guglielmo Scarlato S Barbieri |
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Institution: | (1) Institute of Clinical Neurology, University of Milan, IRCCS Ospedale Maggiore Policlinico, Pad. Ponti, Via Francesco Sforza 35, I-20122 Milano, Italy Tel.: 2/55033818, Fax: 2/55190392, FR |
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Abstract: | Motor conduction block (MCB) has been used as the main diagnostic criterion in multifocal motor neuropathy (MMN). Nonetheless,
no agreed definition of block currently exists; the proposed required percent decrement of proximal compound muscle action
potential (CMAP) amplitude varies from > 20% to > 50%. The aim of this work was to evaluate, through a follow-up study of
patients with MMN, the behaviour of MCB over time. The percent decrement and temporal dispersion of proximal CMAP have also
been calculated in normal controls and in patients affected by amyotrophic lateral sclerosis (ALS). The results show that
MCB in patients with MMN is a dynamic entity which greatly varies over time and that a > 50% CMAP amplitued reduction may
well be preceded by a smaller decrement that is nonetheless indicative of focal myelin damage in the appropriate clinical
context. This datum and the results obtained in the control group and in patients with ALS suggest that a reappraisal of the
diagnostic criteria for MCB, in cases with clinical and electrophysiological data strongly indicative of MMN, should be considered.
Since MMN is a treatable disorder, the use of the proposed less restrictive criteria for the identification of MCB could allow
for a promp and more effective treatment.
Received: 31 December 1996 Received in revised form: 1 August 1997 Accepted: 13 August 1997 |
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Keywords: | Multifocal motor neuropathy Amyotrophic lateral sclerosis Electrophysiological follow-up Conduction block Diagnostic criteria |
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