Multifocal motor neuropathy (MMN) with conduction block (CB) is a rare chronic immune-mediated neuropathy, but important to diagnose as it is treatable. The key features in prototypic MMN are electrodiagnostic demonstration of focal CB away from common sites of entrapment and normal sensory conduction across these sites. However, there are challenges in distinguishing CB from the effects of abnormal temporal dispersion. Consensus electrodiagnostic criteria, reinforced by modeling studies, are available to support definite or probable CB. In addition, consideration of technical issues can guard against false-positive and false-negative conclusions. These include limb temperature, stimulus site, inadvertent stimulating electrode movement, and supramaximal and submaximal responses, as well as the possibility of Martin-Gruber anastamosis. Robust evidence supports the treatment of MMN with intravenous immunoglobulin, and guidelines have been developed. Application of practical and simple rules including a 4-step diagnostic algorithm can help practitioners correctly diagnose this treatable condition and improve patient outcomes.
*Department of Neurology, University of Utah, Salt Lake City, UT; and
†Department of Neurology, Neuromuscular Disease Group, Brain Center Rudolf Magnus, University Medical Center, Utrecht, the Netherlands.
Reprints: Mark B. Bromberg, MD, PhD, Department of Neurology, University of Utah, 175, North Medical Drive, Salt Lake City, UT 84132 (e-mail: email@example.com).
H. Franssen received honoraria and travel reimbursement from Baxter Healthcare Corporation and grants from the Prinses Beatrix Spierfonds and the European Federation of Neurological Societies.
M. B. Bromberg is a medical advisory consultant for Baxter Healthcare Corporation. H. Franssen reports no conflicts of interest.