[Understanding functional neurological disorders: From biological markers to pathophysiological models]

OBJECTIVES

Functional neurological disorders have witnessed intense research activity in the fields of structural and functional neuroimaging for more than twenty years. Thus, we propose a synthesis of recent research findings and etiological hypotheses that have been proposed so far. This work should help clinicians to better understand the nature of the mechanisms involved, but also help patients to increase their knowledge about the biological features underlying their functional symptoms.

METHODS

We carried out a narrative review of international publications dealing with neuroimaging and biology of functional neurological disorders, from 1997 to 2023.

RESULTS

Several brain networks underlie functional neurological symptoms. These networks play a role in the management of cognitive resources, in attentional control, emotion regulation, in agency and in the processing of interoceptive signals. The mechanisms of the stress response are also associated with the symptoms. The biopsychosocial model helps to better understand predisposing, precipitating, and perpetuating factors involved. The functional neurological phenotype results from the interaction between: i) a specific pre-existing vulnerability resulting from biological background and epigenetic modifications, and ii) exposure to stress factors, according to the stress-diathesis model. This interaction causes emotional disturbances including hypervigilance, lack of integration of sensations and affects, and emotional dysregulation. These characteristics in turn impact the cognitive, motor and affective control processes related with the functional neurological symptoms.

CONCLUSIONS

A better knowledge of the biopsychosocial determinants of brain network dysfunctions is necessary. Understanding them would help developing targeted treatments, but is also critical for patients care.

[Functional neurological disorders and forensic medicine: Clinical and practical characteristics]

Functional neurological disorders (FND) have long been a challenge for medicine, both on clinical and psychodynamic point of view. The medico-legal issue is often relegated to the background in medicine, and FND patients also suffer from such neglected topic. Nonetheless, despite the difficulty to properly diagnose FND and the numerous associated organic and/or psychiatric comorbidities, FND patients report a significant level of deficiency and a high alteration of quality of life when compared to other well-recognized chronic disorders such as Parkinson's disease or epilepsy. Whether it is for the estimation of a personal injury, a prejudice, after-effects following a medical accident or certain legal contexts requiring the elimination of a factitious disorder or a simulation, the uncertainty and imprecision in the medico-legal assessment can imply notable consequences on the patient. In this article, we propose to define the different medico-legal contexts in which FND can occur that of the legal expert, that of the consulting physician, that of the so-called recourse physician and finally that of the attending physician who can provide detailed medical files to the patient in order to help him/her in his/her procedures. We then explain how to use standardized objective evaluation tools validated by the learned societies and how to encourage multidisciplinary cross-evaluation. Finally, we specify how to differentiate FND from historically FND-associated disorders (factitious and simulated disorders), through the clinical criteria, considering the difficulties linked to the uncertainty in the clinical examination of these disorders in a medico-legal context. In addition to the rigorous completion of expertise missions, we aim to reduce two damaging consequences characterizing FND: diagnostic delay and the patients' suffering through stigma.

Association between brain metabolism and clinical course of motor functional neurological disorders

Features of resting brain metabolism in motor functional neurological disorder are poorly characterized. This study aimed to investigate the alterations of resting brain metabolism in a cohort of patients experiencing a first episode of motor functional neurological disorder with recent symptom onset, and their association with persistent disability after 3 months. Patients eligible for inclusion were diagnosed with first episode of motor functional neurological disorder, were free from bipolar disorder, substance use disorder, schizophrenia, psychogenic non-epileptic seizure or any chronic or acute organic neurological disorder. Exclusion criteria included current suicidal ideation, antipsychotic intake and previous history of functional neurological disorder. Nineteen patients were recruited in Psychiatry and Neurology departments from 2 hospitals. Resting brain metabolism measured with 18F-fluorodeoxyglucose positron emission computed tomography at baseline and 3 months was compared to 23 controls without neurological impairment. Disability was scored using Expanded Disability Status Scale and National Institutes of Health Stroke Scale score at baseline and 3 months. Correlations were calculated with Spearman correlation coefficient. Hypometabolism was found at baseline in bilateral frontal regions in patients versus controls, disappearing by 3 months. The patients with Expanded Disability Status Scale score improvement showed greater resting state activity of prefrontal dorsolateral cortex, right orbito-frontal cortex and bilateral frontopolar metabolism at 3 months versus other patients. The resting state metabolism of the right subgenual anterior cingular cortex at baseline was negatively correlated with improvement of motor disability (measured with Expanded Disability Status Scale) between inclusion and 3 months (r=-0.75, p = 0.0018) and with change in motor symptoms assessed with the National Institutes of Health Stroke Scale (r=-0.81, p= 0.0005). The resting state metabolism of the left subgenual anterior cingular cortex at baseline was negatively correlated with improvement in Expanded Disability Status Scale and National Institutes of Health Stroke Scale scores between inclusion and 3 months (r= -0.65, p = 0.01 and r= -0.75, p = 0.0021, respectively). The negative association between the brain metabolism of the right subgenual anterior cingular cortex at baseline and change in National Institutes of Health Stroke Scale score remained significant (r=-0.81, p= 0.0414) after correction for multiple comparisons. Our findings suggest the existence of metabolic "state markers" associated with motor disability and that brain markers are associated with motor recovery in functional neurological disorder patients.

Voiding and storage symptoms in depression/anxiety

We here described the frequency and nature of voiding and storage bladder symptoms in depression/anxiety, for which we propose the name "bladder somatic symptom disorder (SSD)" because such symptoms most probably have brain mechanisms. SSD was formerly called as various terms including "somatoform disorder", "medically unexplained physical symptoms", "functional somatic syndrome" and "hysterical neurosis/hysteria". Bladder SSD has the following specific features that are distinguishable from "true" neurologic/organic bladder dysfunction: 1) situation-dependence (close association with life event in some), 2) urodynamically increased bladder sensation/hypersensitivity and 3) absence of neurologic/organic diseases, in addition to 4) other stress symptoms (insomnia, etc.), are key clues to the possibility of bladder SSD. Urodynamics in these patients showed, to a lesser extent, underactive bladder without post-void residual. These findings might reflect the biological changes of the depressive brain; e.g., decreases in serotonin and GABA, and possible increases in CRH. Treatment of bladder SSD can follow that of general depression/anxiety, with the potential addition of anticholinergic or selective beta3 bladder drugs.

Stress response in dissociation and conversion disorders: A systematic review

Dissociative disorders (DD) and conversion disorders (CD) are frequent in general and psychiatric populations. Some evidence suggest that the hypothalamic-pituitary axis (HPA) and autonomic nervous system (ANS) are dysregulated in both disorders. We carried out a systematic review of the literature to summarize the existing knowledge on the stress response, via HPA and/or ANS, in patients with DD, CD, or dissociative symptoms. We systematically searched Medline and Web of Science using the Medical Subject Headings related to stress axis, CD, DD, and dissociative symptoms following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Results suggest that in participants without psychiatric history, high cortisol secretion is related to high dissociation scores. Conversely the stress system might be blunted in patients with post-traumatic stress disorder who develop dissociative symptoms. Stress response changes seem to be associated with the emergence and persistence of dissociative and conversion disorders. Hence, monitoring the stress response and examining closely the history of stress exposure in DD and CD should be encouraged in future larger studies.

Arousability, Personality, and Decision-Making Ability in Dissociative Disorder

BACKGROUND

There is a gap in understanding the pathogenesis of dissociative conversion disorder (DCD), despite the disorder having a strong historical root. The role of personality and neurocognitive factors are now highlighted; however, inconsistencies are reported. This study explores the personality disposition, arousability, and decision-making ability of patients with DCD, in reference to a healthy control group (HCG).

METHODS

In this cross-sectional study, the sample comprised ten adult psychiatric patients with DCD. Ten participants of the HCG were matched according to age, gender, education, economic status, domicile, religious background, and handedness. The study assessed personality disposition with Temperament and Character Inventory, arousability with reaction time task, and decision-making ability with the Iowa Gambling Task (IGT PEBL version).

RESULTS

The DCD group differed significantly on personality disposition related to both temperament and character. There was also evidence of easy arousability and frustration along with deficit in executive function related to decision-making ability.

CONCLUSION

This study highlights the presence of both temperamental and characterological factors associated with DCD. Moreover, this study identifies the role of cognitive arousability and decision-making or feedback utilization ability in the psychopathology of DCD.

Increased Amygdala Activity Associated With Cognitive Reappraisal Strategy in Functional Neurologic Disorder

Cognitive reappraisal is an emotion regulation strategy to reduce the impact of affective stimuli. This regulation could be incomplete in patients with functional neurologic disorder (FND) resulting in an overflowing emotional stimulation perpetuating symptoms in FND patients. Here we employed functional MRI to study cognitive reappraisal in FND. A total of 24 FND patients and 24 healthy controls employed cognitive reappraisal while seeing emotional visual stimuli in the scanner. The Symptom Checklist-90-R (SCL-90-R) was used to evaluate concomitant psychopathologies of the patients. During cognitive reappraisal of negative IAPS images FND patients show an increased activation of the right amygdala compared to normal controls. We found no evidence of downregulation in the amygdala during reappraisal neither in the patients nor in the control group. The valence and arousal ratings of the IAPS images were similar across groups. However, a subgroup of patients showed a significant higher account of extreme low ratings for arousal for negative images. These low ratings correlated inversely with the item "anxiety" of the SCL-90-R. The increased activation of the amygdala during cognitive reappraisal suggests altered processing of emotional stimuli in this region in FND patients.

Structural neuroimaging of somatoform disorders: A systematic review

Although there has been an increment in neuroimaging research in somatoform disorders (SD), to date little is known about the neural correlates of these diseases. Therefore, in this systematic, review we aimed at summarizing the existing evidence of structural brain alterations in SD as per DSM-IV and DSM-5 criteria. Three electronic databases (Scopus, PubMed and Web of Science) were searched. Only case-control studies using structural neuroimaging were included. Forty-five out of 369 articles fulfilled inclusion criteria and were reviewed. Compared to controls, subjects with SD showed morphological alterations encompassing motor, limbic and somatosensory circuits. Although far from being conclusive, the results suggested that SD are characterized by selective alterations of large-scale brain networks implicated in cognitive control, emotion regulation and processing, stress and somatic-visceral perception. This review highlights the need for further multimodal neuroimaging studies with longitudinal designs, in larger and better-characterized samples, to elucidate the temporal and causal relationship between neuroanatomical changes and SD, which is paramount for informing tailored treatments.

Impaired Action Control in Patients With Functional Movement Disorders

OBJECTIVE

Despite being a major cause of neurological disability, the neural mechanisms of functional movement disorders (FMDs) remain poorly understood. Recent studies suggest that FMD is linked to dysfunctional motor and prefrontal regions that could lead to motor and cognitive impairments. The aim of this study was to investigate different components of action control in FMD by using choice-reaction, stop-signal, and Simon tasks.

METHODS

Thirty patients with an FMD were prospectively recruited from the University of Louisville Movement Disorders Clinic and compared with 53 healthy control subjects, recruited from the Vanderbilt University Medical Center Movement Disorders Clinic. FMD motor symptom severity was rated with the Simplified Functional Movement Disorder Rating Scale (S-FMDRS). By using a computer and handheld response grips, participants completed three action-control tasks (choice-reaction task, stop-signal task, and Simon task) that tested action initiation, action cancelation, and interference control over actions. Action-control measures were compared between groups with analyses of variance.

RESULTS

Patients with FMD were less proficient in suppressing incorrect response impulses on the Simon task and were slower to stop on the stop-signal task compared with healthy control subjects. No significant correlation with neuropsychological measurements, S-FMDRS scores, and action-control measurements was observed.

CONCLUSIONS

These results suggest that two forms of inhibitory control, selective impulse inhibition and global action cancelation, are impaired in patients with FMD, independent of slowing on go reaction times. Improved understanding of action control in FMD may help in the development of new diagnostic and therapeutic strategies.

Functional Neurological Symptom Disorder: A Diagnostic Algorithm

Functional neurological symptom disorder (FNSD) is a neuropsychiatric disorder characterized by the presence of neurological symptoms in the absence of any neurological abnormality that can be linked to a known pathology. Few studies have taken interest in this subject probably because of the heterogeneity of results. It is most often a diagnosis of exclusion which often means that patients undergo many tests and find themselves erring for a diagnosis with very little satisfaction of the outcomes. A reliable imagery pattern would therefore provide some relief and confirmation for both patients and clinicians. It could also facilitate acceptation of the diagnosis and reduce the societal cost associated with FNSD for the patient. The aim of this present study was to describe a clinicoradiological correspondence algorithm of FNSD using the PET scan and SPECT scan (PoSPs) and grant the clinician with a reliable tool to facilitate the diagnosis of FNSD. A systematic review according to the 2009 PRISMA criteria statement was used to guide the review. Our study included 3 of our own consenting patients who met the Diagnostic and Statistical Manual of Mental Disorders 5^th edition criteria as well as 25 other patients from 7 different studies. Our results showed a hypoactivation with poor clinicoradiological correspondence and poor stability in time. This hypoactivation was mostly in the frontal lobe, which could explain some behavioral alterations. These findings oppose the ones found in organic pathologies and therefore should orient towards FNSD. In the light of these findings, we recommend the clinicians to perform two PoSPs, searching for clinicoradiological lack of correspondence and time stability using our algorithm.

Functional neuroimaging in patients presenting with somatoform disorders: A model for investigating persisting symptoms after tick bites and post-treatment Lyme disease syndrome?

Approximately 10% of patients presenting with Lyme disease experience fatigue, musculoskeletal pain, concentration disorders, or short-term memory deficits in the six months following treatment. This entity has been defined as post-Lyme disease syndrome or post-treatment Lyme disease syndrome. The pathophysiology of this syndrome is unknown, but neither persistence of the bacterium nor effectiveness of antibiotics are currently reported in the literature. The French High Council for Public Health (French acronym HCSP) has recently defined a new entity called "persistent polymorphic symptoms after a tick bite" allowing for designing studies to better understand these subjective presentations, for which objective biomarkers are currently lacking. This entity encompasses patients experiencing fatigue and generalized pain in the months following a tick bite and can be associated with several subjective symptoms with major impact on the quality of life. In the field of somatoform disorders, this article reviews functional neuroimaging studies in patients presenting with subjective complaints and discusses potential clinical implications for persisting symptoms after tick bites and post-treatment Lyme disease syndrome.