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CC BY 4.0 · Arq Neuropsiquiatr 2025; 83(02): s00451806818
DOI: 10.1055/s-0045-1806818
Original Article

Radial motor nerve conduction study in posterior interosseous nerve syndrome and multifocal motor neuropathy

José Pedro S. Baima 
1   Universidade de São Paulo, Departamento de Neurologia, São Paulo SP, Brazil.
2   Universidade Federal do Ceará, Unidade do Sistema Nervoso, Fortaleza CE, Brazil.
,
Carlos Otto Heise 
1   Universidade de São Paulo, Departamento de Neurologia, São Paulo SP, Brazil.
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Abstract

Background Finger extension weakness could be a presentation of either posterior interosseous nerve (PIN) syndrome or multifocal motor neuropathy (MMN). However, there is a delay in the diagnosis of MMN in cases with a selective radial weakness, as they are frequently misdiagnosed as PIN.

Objective To analyze which variables in nerve conduction studies could aid in the early diagnosis of MMN.

Methods We reviewed charts of patients with diagnoses of MMN or PIN syndrome, from 2014 to 2022, in a single Brazilian reference center. Electrophysiological parameters included in the analysis were motor conduction velocity (CV), the presence and magnitude of conduction block (CB), distal motor latencies (DML), and the compound muscle action potential amplitude (CMAP) of the affected radial nerve.

Results A total of 44 radial nerves were included in the study. Axonal loss was associated with a diagnosis of PIN syndrome, while conduction block was associated with MMN (p < 0.05). No patient with PIN had a CB over 60%, while 7 out of 12 radial CB blocks in patients with MMN were above that. Axonal degeneration was present in 4 MMN patients and in all patients with PIN syndrome. There was no difference in CV and DML between groups.

Conclusion The presence of CB or the absence of distal CMAP amplitude reduction should lead physicians to consider MMN, and a comprehensive nerve conduction study should be performed.

Keywords

Peripheral Nervous System Diseases - Radial Neuropathy - Nerve Compression Syndromes - Electromyography

Authors' Contributions

Conceptualization: JPSB, COH; Data curation: JPSB, COH; Formal analysis: JPSB, COH; Funding acquisition: JPSB, COH; Investigation: JPSB, COH; Methodology: JPSB, COH; Project administration: JPSB, COH; Writing - original draft: JPSB, COH; Writing - review & editing: JPSB, COH.


Data Availability Statement

The data that support the findings of this study are available upon reasonable request.


Editor-in-Chief: Hélio A. G. Teive.


Associate Editor: Paulo José Lorenzoni.




Publication History

Received: 30 October 2024

Accepted: 17 December 2024

Article published online:
27 April 2025

© 2025. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution 4.0 International License, permitting copying and reproduction so long as the original work is given appropriate credit (https://creativecommons.org/licenses/by/4.0/)

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Bibliographical Record
José Pedro S. Baima, Carlos Otto Heise. Radial motor nerve conduction study in posterior interosseous nerve syndrome and multifocal motor neuropathy. Arq Neuropsiquiatr 2025; 83: s00451806818.
DOI: 10.1055/s-0045-1806818
 

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