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Journal of Clinical and

Basic Psychosomatics

REVIEW ARTICLE
Functional neurological disorder and gut

microbiome: Casual or causal relationship?

Alejandro Borrego-Ruiz * , and Juan J. Borrego 2
1
1 Department of Social and Organizational Psychology, National University of Distance Education
(UNED), Madrid, Spain
2 Department of Microbiology, University of Malaga, Malaga, Spain

Abstract

Functional neurological disorder (FND), or conversion disorder, is a psychosomatic
condition that affects the voluntary motor and/or sensory functions of the patient.
Its origin is not yet fully understood, but the main risk factors related to this disorder
include exposure to recent psychological stressors and previous experience of
aversive episodes during childhood, such as abuse, family dysfunction, and neglect.
The symptoms of FND result from complex interactions involving the central nervous
system and also the endocrine and immune systems. In this work, we hypothesized the
relationship between the gut microbiome and the pathophysiology of FND because
both share several common features, such as the effects of neurotransmitters, the
hippocampal expression of brain-derived neurotrophic factor, and the inflammatory
responses. Based on these common aspects, we suggested that stress, gut
microbiome, and inflammation factors induce chronic and systemic inflammation of
the brain causing neurological disorders, including FND. More specific studies are
*Corresponding author: warranted to validate the casual or causal relationship between FND and the gut
Alejandro Borrego-Ruiz microbiome.
(a.borrego@psi.uned.es)
Citation: Borrego-Ruiz A, Borrego
JJ. Functional neurological disorder Keywords: Functional neurological disorder; Conversion disorder; Gut microbiome;
and gut microbiome: Casual or Neurotransmitters; Microbial metabolites; Neuroinflammation
causal relationship? J Clin Basic
Psychosom. 2024;2(4):4160.
doi: 10.36922/jcbp.4160
Received: July 7, 2024 1. Introduction
Accepted: August 2, 2024 Psychosomatic disorders affect both body and mind, and these conditions are mainly
Published Online: September 19, characterized by physical symptoms that result from psychological causes such as stress,
2024 anxiety, and depression. In the past decades, there has been a rapid increase in the
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Copyright: © 2024 Author(s). prevalence rates of psychosomatic disorders as a result of the swiftly changing modern
This is an Open-Access article lifestyle of people, as well as due to long-standing emotional, social, and occupational
distributed under the terms of the
2
Creative Commons Attribution stress. Historically, the term “psychosomatic” was first used by the German psychiatrist
License, permitting distribution, Johann Christian August Heinroth in 1818, while the term “psychosomatic medicine”
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and reproduction in any medium, was introduced by Felix Deutsch in 1922. Sigmund Freud systematically studied the now-
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provided the original work is
5,6
properly cited. famous case of “Anna O,” who suffered from what was then called hysteria. Explaining
the mechanisms of the psychosomatic disorder of alexithymia, Nemiah et al. stated in 1976
Publisher’s Note: AccScience
Publishing remains neutral with that emotional reactions occur in two dimensions: psychological and vegetative states. 7
regard to jurisdictional claims in
published maps and institutional Functional neurological disorder (FND), or conversion disorder, is a psychosomatic
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affiliations. condition affecting the voluntary motor or sensory function of the patient, in which
Volume 2 Issue 4 (2024) 1 doi: 10.36922/jcbp.4160