Short ReportSevere Paraproteinemic Demyelinating Neuropathy With Impaired Excitability of the Distal Segments of the Peripheral NervesKhodulev, Vasily I. MD, PhD*; Kabaeva, Katsiaryna N. MD, PhD†; Stepanova, Julia I. PhD‡; Shcharbina, Natallia Y. PhD§Author Information *Functional Diagnostics Department, Republican Research and Clinical Center of Neurology and Neurosurgery, Minsk, Belarus; †Department of Clinical Hematology and Transfusiology, Belarusian Medical Academy of Postgraduate Education, Minsk, Belarus; ‡Scientific Research Laboratory, Belarusian Medical Academy of Postgraduate Education, Minsk, Belarus; and §Clinical Unit “Eleous” at Religious Community, “All Saints Parish in Minsk Eparchy of Belarusian Orthodox Church”, Minsk, Belarus. Reprints: Vasily I. Khodulev, MD, PhD, Functional Diagnostics Department, Republican Research and Clinical Center of Neurology and Neurosurgery, F. Skariny Street 24, Minsk, 220114 Belarus (e-mail: [email protected]). The authors report no conflicts of interest. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.jcnmd.com). Journal of Clinical Neuromuscular Disease: September 2021 - Volume 23 - Issue 1 - p 43-48 doi: 10.1097/CND.0000000000000357 Buy SDC Metrics Abstract We report clinical and detailed nerve conduction findings in case of polyneuropathy associated with kappa light chains monoclonal gammopathy of undetermined significance with progression to lymphoproliferative disorder. A 55-year-old man had a predominantly distal, chronic (5 years duration), slowly progressive, symmetric, predominantly sensory impairment with sensory ataxia, and mild weakness. M protein was identified by serum protein electrophoresis. The kappa/lambda ratio of free light chains was significantly elevated to 11.96. The cerebrospinal fluid protein level was elevated at 3.5 g/L. This case study has revealed 2 unusual electrophysiological phenomena—a very unusual prolongation of distal motor latencies of compound muscle action potentials (CMAP) up to 86.5 ms and impaired excitability of the distal segments of the peripheral nerves. The distal CMAP areas were considerably lower compared with the proximal CMAP areas. Radiography of the skull revealed osteolytic lesions. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.