Functional neurological disorder and gut microbiome: Casual or causal relationship?

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 warranted to validate the casual or causal relationship between FND and the gut microbiome.