Delayed Appearance of Conduction Block in Multifocal Motor Neuropathy—A Case Report

US Neurology, 2017;13(2):99–102 DOI: https://doi.org/10.17925/USN.2017.13.02.99

Abstract:

Introduction: Multifocal motor neuropathy (MMN) is a rare, treatable, immune-mediated neuropathy often associated with multifocal conduction block (CB). The hallmark electrodiagnostic feature is the presence of CB occurring at non-entrapment sites. However, MMN without CB has also been described and can be diagnosed, even in the absence of CB. Therefore, it is crucial to diagnose and identify MMN cases without CB, as it is a treatable disorder. Case presentation: We present a case with progressive symptoms of asymmetric distal upper and lower extremity weakness with no sensory deficits. Intravenous immunoglobulin (IVIG) therapy was initiated, as the patient fulfilled the criteria for probable MMN, despite the absence of CB. The patient’s symptoms demonstrated a relative plateau phase in response to IVIG. Although the patient lost follow-up visits, repeated electrodiagnostic study, conducted 11 years after initial presentation, revealed new CB in nerve segments that previously did not show any evidence of CB. Conclusion: This case emphasizes the importance of early diagnosis and respectively initiating early IVIG treatment in MMN, in order to maintain the clinical function. Underdiagnosis of clinically suspected MMN, based on absence of CB, will result in denial of treatment to potential IVIG responders.
Keywords: Multifocal motor neuropathy, conduction block, intravenous immunoglobulin
Disclosure: Said R Beydoun has received grant research support from Alexion, Argenx, Daiichi Pharma, and Pfizer. He has served as an advisory board member for Grifols, MT Pharma and Sarepta, and is a speaker for Grifols. Leila Darki has nothing to disclose in relation to this article.

Authorship: All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship of this manuscript, take responsibility for the integrity of the work as a whole, and have given final approval to the version to be published.

Compliance with Ethics: All procedures were followed in accordance with the responsible committee on human experimentation and with the Helsinki Declaration of 1975 and subsequent revisions. Written informed consent was not obtained from the patient for publication of this case report due to loss of follow-up; no identifying information or images were used in the publication of this paper.

Received: June 12, 2017 Accepted August 02, 2017
Correspondence: Leila Darki, Neuromuscular Division, Keck School of Medicine, University of Southern California, 1520 San Pablo St, Suite 3000, Los Angeles, CA 90033, US. E: Leila.darki@med.usc.edu
Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any non-commercial use, distribution, adaptation and reproduction provided the original author(s) and source are given appropriate credit.

Keywords: Multifocal motor neuropathy, conduction block, intravenous immunoglobulin