Reduced drift rate: a biomarker of impaired information processing in functional movement disorders

Increased beta synchronization underlies perception-action hyperbinding in functional movement disorders

Functional movement disorders are amongst the most common and disabling neurological conditions, placing a significant burden on the healthcare system. Despite the frequency and importance of functional movement disorders, our understanding of the underlying pathophysiology is limited, hindering the development of causal treatment options. Traditionally, functional movement disorders were considered as a psychiatric condition, associated with involuntary movements triggered by psychological stressors. Recent neurophysiological studies have unveiled cognitive alterations in affected individuals, suggesting that functional movement disorders might be better characterized by overarching neural principles governing cognitive functions. For instance, recent research has shown that the retrieval of stimulus-response bindings is altered in patients with functional movement disorders. Building upon these recent findings, our study delves into whether the initial integration of stimulus and response information is also disrupted in patients with functional movement disorders. To accomplish this, we reanalysed previously collected EEG data using refined analysis methods that provide insights into oscillatory activity and functional neuroanatomy associated with the integration of stimulus-response bindings. Our results demonstrate that post-movement beta synchronization (i) predicts behavioural stimulus-response binding and (ii) is significantly increased in patients with functional movement disorders compared to healthy controls. Utilizing beamformer analysis, we localized the difference effect to a cluster centred around the left supplementary motor area and the correlation effect to the right supplementary motor area. Extending beyond recent research that focused on the retrieval of stimulus-response bindings, our present findings reveal that the integration of stimulus and response information is already impaired in patients with functional movement disorders. These results uncover a phenomenon of hyperbinding between perception and action, which may represent a fundamental mechanism contributing to the movement impairments in patients with functional movement disorders.

Biomarkers and Rehabilitation for Functional Neurological Disorder

Functional neurological disorder, or FND, is widely misunderstood, particularly when considering recent research indicating that the illness has numerous biological markers in addition to its psychiatric disorder associations. Nonetheless, the long-held view that FND is a mental illness without a biological basis, or even a contrived (malingered) illness, remains pervasive both in current medical care and general society. This is because FND involves intermittent disability that rapidly and involuntarily alternates with improved neurological control. This has in turn caused shaming, perceived low self-efficacy, and social isolation for the patients. Until now, biomarker reviews for FND tended not to examine the features that are shared with canonical neurological disorders. This review, in contrast, examines current research on FND biomarkers, and in particular their overlap with canonical neurological disorders, along with the encouraging outcomes for numerous physical rehabilitation trials for FND. These findings support the perspective endorsed here that FND is unquestionably a neurological disorder that is also associated with many biological markers that lie outside of the central nervous system. These results suggest that FND entails multiple biological abnormalities that are widely distributed in the body. General healthcare providers would benefit their care for their patients through their improved understanding of the illness and recourses for support and treatment that are provided in this review.

Loss and Return of Ticklishness in Functional Neurological Disorder

BACKGROUND

People with functional neurological disorder (FND) have abnormalities in sensory processing. Loss of ticklishness has been rarely reported.

OBJECTIVES

To describe associated clinical features in people with FND and loss of ticklishness and explore correlations with sensory changes.

METHODS

Retrospective audit of clinical letters of people diagnosed with FND in a tertiary clinic and further cases identified in a general neurology clinic.

RESULTS

Thirty-eight patients with loss of ticklishness are described, of which most had other functional sensory symptoms and signs. It was more often localized to one limb, rather than generalized, in those with pain or weakness. Dissociation for the affected body part was often described.

CONCLUSIONS

Loss of ticklishness in FND is frequently described and offers insights into mechanisms of agency, sensory processing and interoception, which are known to be altered in FND.

Virtual reality in functional neurological disorder: a theoretical framework and research agenda for use in the real world

Functional neurological disorder (FND) is a common and disabling condition at the intersection of neurology and psychiatry. Despite remarkable progress over recent decades, the mechanisms of FND are still poorly understood and there are limited diagnostic tools and effective treatments. One potentially promising treatment modality for FND is virtual reality (VR), which has been increasingly applied to a broad range of conditions, including neuropsychiatric disorders. FND has unique features, many of which suggest the particular relevance for, and potential efficacy of, VR in both better understanding and managing the disorder. In this review, we describe how VR might be leveraged in the treatment and diagnosis of FND (with a primary focus on motor FND and persistent perceptual-postural dizziness given their prominence in the literature), as well as the elucidation of neurocognitive mechanisms and symptom phenomenology. First, we review what has been published to date on the applications of VR in FND and related neuropsychiatric disorders. We then discuss the hypothesised mechanism(s) underlying FND, focusing on the features that are most relevant to VR applications. Finally, we discuss the potential of VR in (1) advancing mechanistic understanding, focusing specifically on sense of agency, attention and suggestibility, (2) overcoming diagnostic challenges and (3) developing novel treatment modalities. This review aims to develop a theoretical foundation and research agenda for the use of VR in FND that might be applicable or adaptable to other related disorders.

[Interpretation of a concept for functional movement disorders from the perspective of older patients]

A recently published concept considers a significant proportion of the occurrence and persistence of functional movement disorders (FMD) to be explained by increased/incorrect weighting of the expected movement (feedforward signal) in the presence of decreased/altered actual feedback of the movement. In the context of aging and age-associated diseases, there is an increased likelihood that these prerequisites will occur, also in combination. For example, the feedforward signal can be enhanced by accumulation of a wealth of experience but can for example become prone to error due to changes in attention and (fear of) falling. Conversely, the actual feedback is subject to age-related changes, such as reduction of sensory functions. This could explain why FMDs also occur in old age and offer treatment approaches for this so far poorly studied disorder. It follows that a specific focus on (the correction of) feedforward signals and strengthening as well as training of the actual feedback are potentially promising therapeutic approaches for older people with FMD.

Predictive Processing and the Pathophysiology of Functional Neurological Disorder

The contemporary neuroscience understanding of the brain as an active inference organ supports that our conscious experiences, including sensorimotor perceptions, depend on the integration of probabilistic predictions with incoming sensory input across hierarchically organized levels. As in other systems, these complex processes are prone to error under certain circumstances, which may lead to alterations in their outcomes (i.e., variations in sensations and movements). Such variations are an important aspect of functional neurological disorder, a complex disorder at the interface of brain-mind-body interactions. Thus, predictive processing frameworks offer fundamental mechanistic insights into the pathophysiology of functional neurological disorder. In recent years, many of the aspects relevant to the neurobiology of functional neurological disorder - e.g., aberrant motor and sensory processes, symptom expectation, self-agency, and illness beliefs, as well as interoception, allostasis, and emotion - have been investigated through the lens of predictive processing frameworks. Here, we provide an overview of the current state of research on predictive processing and the pathophysiology of functional neurological disorder.

How Does Postural Control in Patients with Functional Motor Disorders Adapt to Multitasking-Based Immersive Virtual Reality?

BACKGROUND

Motor symptoms in functional motor disorders (FMDs) refer to involuntary, but learned, altered movement patterns associated with aberrant self-focus, sense of agency, and belief/expectations. These conditions commonly lead to impaired posture control, raising the likelihood of falls and disability. Utilizing visual and cognitive tasks to manipulate attentional focus, virtual reality (VR) integrated with posturography is a promising tool for exploring postural control disorders.

OBJECTIVES

To investigate whether postural control can be adapted by manipulating attentional focus in a 3D immersive VR environment.

METHODS

We compared postural parameters in 17 FMDs patients and 19 age-matched healthy controls over a single session under four increasingly more complex and attention-demanding conditions: simple fixation task (1) in the real room and (2) in 3D VR room-like condition; complex fixation task in a 3D VR city-like condition (3) avoiding distractors and (4) counting them. Dual-task effect (DTE) measured the relative change in performance induced by the different attention-demanding conditions on postural parameters.

RESULTS

Patients reduced sway area and mediolateral center of pressure displacement velocity DTE compared to controls (all, P < 0.049), but only under condition 4. They also showed a significant reduction in the sway area DTE under condition 4 compared to condition 3 (P = 0.025).

CONCLUSIONS

This study provides novel preliminary evidence for the value of a 3D immersive VR environment combined with different attention-demanding conditions in adapting postural control in patients with FMDs. As supported by quantitative and objective posturographic measures, our findings may inform interventions to explore FMDs pathophysiology.

Motor Decision-Making as a Common Denominator in Motor Pathology and a Possible Rehabilitation Target

Despite the substantial progress in motor rehabilitation, patient involvement and motivation remain major challenges. They are typically addressed with communicational and environmental strategies, as well as with improved goal-setting procedures. Here we suggest a new research direction and framework involving Neuroeconomics principles to investigate the role of Motor Decision-Making (MDM) parameters in motivational component and motor performance in rehabilitation. We argue that investigating NE principles could bring new approaches aimed at increasing active patient engagement in the rehabilitation process by introducing more movement choice, and adapting existing goal-setting procedures. We discuss possible MDM implementation strategies and illustrate possible research directions using examples of stroke and psychiatric disorders.

Perception-Action Integration Is Altered in Functional Movement Disorders

BACKGROUND

Although functional neurological movement disorders (FMD) are characterized by motor symptoms, sensory processing has also been shown to be disturbed. However, how the integration of perception and motor processes, essential for the control of goal-directed behavior, is altered in patients with FMD is less clear. A detailed investigation of these processes is crucial to foster a better understanding of the pathophysiology of FMD and can systematically be achieved in the framework of the theory of event coding (TEC).

OBJECTIVE

The aim was to investigate perception-action integration processes on a behavioral and neurophysiological level in patients with FMD.

METHODS

A total of 21 patients and 21 controls were investigated with a TEC-related task, including concomitant electroencephalogram (EEG) recording. We focused on EEG correlates established to reflect perception-action integration processes. Temporal decomposition allowed to distinguish between EEG codes reflecting sensory (S-cluster), motor (R-cluster), and integrated sensory-motor processing (C-cluster). We also applied source localization analyses.

RESULTS

Behaviorally, patients revealed stronger binding between perception and action, as evidenced by difficulties in reconfiguring previously established stimulus-response associations. Such hyperbinding was paralleled by a modulation of neuronal activity clusters, including reduced C-cluster modulations of the inferior parietal cortex and altered R-cluster modulations in the inferior frontal gyrus. Correlations of these modulations with symptom severity were also evident.

CONCLUSIONS

Our study shows that FMD is characterized by altered integration of sensory information with motor processes. Relations between clinical severity and both behavioral performance and neurophysiological abnormalities indicate that perception-action integration processes are central and a promising concept for the understanding of FMD. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The complex syndrome of functional neurological disorder

BACKGROUND

Patients with functional neurological disorders (FND) often present with multiple motor, sensory, psychological and cognitive symptoms. In order to explore the relationship between these common symptoms, we performed a detailed clinical assessment of motor, non-motor symptoms, health-related quality of life (HRQoL) and disability in a large cohort of patients with motor FND. To understand the clinical heterogeneity, cluster analysis was used to search for subgroups within the cohort.

METHODS

One hundred fifty-two patients with a clinically established diagnosis of motor FND were assessed for motor symptom severity using the Simplified Functional Movement Disorder Rating Scale (S-FMDRS), the number of different motor phenotypes (i.e. tremor, dystonia, gait disorder, myoclonus, and weakness), gait severity and postural instability. All patients then evaluated each motor symptom type severity on a Likert scale and completed questionnaires for depression, anxiety, pain, fatigue, cognitive complaints and HRQoL.

RESULTS

Significant correlations were found among the self-reported and all objective motor symptoms severity measures. All self-reported measures including HRQoL correlated strongly with each other. S-FMDRS weakly correlated with HRQoL. Hierarchical cluster analysis supplemented with gap statistics revealed a homogenous patient sample which could not be separated into subgroups.

CONCLUSIONS

We interpret the lack of evidence of clusters along with a high degree of correlation between all self-reported and objective measures of motor or non-motor symptoms and HRQoL within current neurobiological models as evidence to support a unified pathophysiology of 'functional' symptoms. Our results support the unification of functional and somatic syndromes in classification schemes and for future mechanistic and therapeutic research.

Why functional neurological disorder is not feigning or malingering

Functional neurological disorder (FND) is one of the commonest reasons that people seek help from a neurologist and is for many people a lifelong cause of disability and impaired quality of life. Although the evidence base regarding FND pathophysiology, treatment and service development has grown substantially in recent years, a persistent ambivalence remains amongst health professionals and others as to the veracity of symptom reporting in those with FND and whether the symptoms are not, in the end, just the same as feigned symptoms or malingering. Here, we provide our perspective on the range of evidence available, which in our view provides a clear separation between FND and feigning and malingering. We hope this will provide a further important step forward in the clinical and academic approach to people with FND, leading to improved attitudes, knowledge, treatments, care pathways and outcomes.

The borderland of multiple sclerosis and functional neurological disorder: A call for clinical research and vigilance

BACKGROUND AND PURPOSE

Functional neurological disorders (FNDs) have attracted much attention from the neurological medical community over the last decades as new developments in neurosciences have reduced stigma around these by showing brain network dysfunctions. An overlap with other neurological conditions such as multiple sclerosis (MS) is well known by clinicians but there is a lack of clinical and fundamental research in this field to better define diagnosis and therapeutic decisions, as well as a lack of deep understanding of the underlying pathophysiology.

AIM

We aimed to provide a critical commentary on the state of knowledge about the borderland between FNDs and MS.

METHODS

We based our commentary on a joint point of view between an FND specialist and an MS expert.

RESULTS

A brief review of the previous literature and relevant new studies covering the overlap between FNDs and MS is presented, along with suggestions for future research directions.

CONCLUSION

There are clear diagnostic criteria for both FNDs and MS and a strict application of these will help better diagnosis and prevent unnecessary treatment escalation in MS or absence of referral to multimodal therapy in FND. Better teaching of younger neurologists is needed as well as prospective research focusing on pathophysiology.

Dysfunctional Networks in Functional Dystonia

Functional dystonia, the second most common functional movement disorder, is characterized by acute or subacute onset of fixed limb, truncal, or facial posturing, incongruent with the action-induced, position-sensitive, and task-specific manifestations of dystonia. We review neurophysiological and neuroimaging data as the basis for a dysfunctional networks in functional dystonia. Reduced intracortical and spinal inhibition contributes to abnormal muscle activation, which may be perpetuated by abnormal sensorimotor processing, impaired selection of movements, and hypoactive sense of agency in the setting of normal movement preparation but abnormal connectivity between the limbic and motor networks. Phenotypic variability may be related to as-yet undefined interactions between abnormal top-down motor regulation and overactivation of areas implicated in self-awareness, self-monitoring, and active motor inhibition such as the cingulate and insular cortices. While there remain many gaps in knowledge, further combined neurophysiological and neuroimaging assessments stand to inform the neurobiological subtypes of functional dystonia and the potential therapeutic applications.

Updates in Functional Movement Disorders: from Pathophysiology to Treatment Advances

Purpose of Review

This review discusses advances in functional movement disorders (FMD) over the past 3 years, with a focus on risk factors, diagnosis, pathophysiology, neuroimaging studies, and treatment.

Recent Findings

The past decade has brought a revived interest in functional movement disorders, with a growing number of studies exploring pathophysiological mechanisms. Here, we review recent studies demonstrating changes in attention, emotional and sensorimotor function in FMD. Through international collaborative efforts, progress has been made in defining biomarkers and outcome measures, an important prerequisite towards standardization of diagnosis and reporting of outcomes in clinical trials. Of particular interest are neuroimaging studies demonstrating functional and structural changes in motor and emotional brain circuits, deepening our understanding of FMD as a neurocircuit disorder and potentially paving the way towards new treatments. Currently available treatment modalities have shown successful outcomes via outpatient, inpatient, and virtual delivery.

Summary

The last 3 years have seen tremendous efforts to better understand, diagnose, and treat FMD. The disease model has been broadened to include a biopsychosocial formulation, and insights on the pathophysiology on FMD are informing treatment efforts. Several international multidisciplinary research collaborations are underway to define biomarkers and best outcome measures, highlighting the path towards improved standardization of future treatment trials. Additionally, the rise of telemedicine during the COVID-19 pandemic has reduced geographic barriers and paved the way for virtual therapy sessions and self-guided programs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11910-022-01192-9.

Functional neurological disorder: new subtypes and shared mechanisms

Functional neurological disorder is common in neurological practice. A new approach to the positive diagnosis of this disorder focuses on recognisable patterns of genuinely experienced symptoms and signs that show variability within the same task and between different tasks over time. Psychological stressors are common risk factors for functional neurological disorder, but are often absent. Four entities-functional seizures, functional movement disorders, persistent perceptual postural dizziness, and functional cognitive disorder-show similarities in aetiology and pathophysiology and are variants of a disorder at the interface between neurology and psychiatry. All four entities have distinctive features and can be diagnosed with the support of clinical neurophysiological studies and other biomarkers. The pathophysiology of functional neurological disorder includes overactivity of the limbic system, the development of an internal symptom model as part of a predictive coding framework, and dysfunction of brain networks that gives movement the sense of voluntariness. Evidence supports tailored multidisciplinary treatment that can involve physical and psychological therapy approaches.

Evaluation of Individualized Multi-Disciplinary Inpatient Treatment for Functional Movement Disorders

BACKGROUND

Functional movement disorders (FMD) are associated with considerable morbidity and impairment of quality of life. Specialized treatment is scarce and data on efficacy of different therapies are limited.

OBJECTIVE

To evaluate a multi-modal inpatient treatment program for patients with FMD.

METHODS

Thirty-one patients with FMD were analyzed before (t1) and after multi-modal inpatient treatment (t2) by a blinded video rating using the Psychogenic Movement Disorder Rating Scale (PMDRS), the simplified Functional Movement Disorder Rating Scale (S-FMDRS), and the Clinical Global Impression Scale of Severity (CGI-S), as well as patients' self-rating. In 23 out of 31 patients a 5 months follow-up investigation was performed (t3). Wilcoxon signed-rank test and Friedman test were used for rating scale and self-rating comparisons over time. Spearman correlation was used for correlation of symptom improvement and clinical characteristics.

RESULTS

Video rating revealed significant reduction of scores after therapy (median PMDRS t1 = 24, t2 = 8, P = 0.0006; S-FMDRS t1 = 11, t2 = 4, P = 0.008; CGI-S t1 = 4, t2 = 3, P = 0.000136) with sustained score decrease in follow-up evaluations (PMDRS t1 = 31, t2 = 8, t3 = 7, P = 0.000032; S-FMDRS t1 = 12, t2 = 4, t3 = 3, P = 0.000888; CGI-S t1 = 4, t2 = 3, t3 = 3, P = 0.000032). Patients reported a stable reduction of symptoms in the self-rating (CGI-S t1 = 5, t2 = 4, t3 = 4, P = 0.016). Age correlated with treatment response with older patients showing better improvement, but disease duration did not correlate with outcome. Patients who suffered from physical trauma, sexual or physical abuse had smaller score reductions.

CONCLUSION

Blinded video and self-rating assessment showed significant score reduction in patients with FMD after an individualized interdisciplinary inpatient intervention.

Dystonia Management: What to Expect From the Future? The Perspectives of Patients and Clinicians Within DystoniaNet Europe

Improved care for people with dystonia presents a number of challenges. Major gaps in knowledge exist with regard to how to optimize the diagnostic process, how to leverage discoveries in pathophysiology into biomarkers, and how to develop an evidence base for current and novel treatments. These challenges are made greater by the realization of the wide spectrum of symptoms and difficulties faced by people with dystonia, which go well-beyond motor symptoms. A network of clinicians, scientists, and patients could provide resources to facilitate information exchange at different levels, share mutual experiences, and support each other's innovative projects. In the past, collaborative initiatives have been launched, including the American Dystonia Coalition, the European Cooperation in Science and Technology (COST-which however only existed for a limited time), and the Dutch DystonieNet project. The European Reference Network on Rare Neurological Diseases includes dystonia among other rare conditions affecting the central nervous system in a dedicated stream. Currently, we aim to broaden the scope of these initiatives to a comprehensive European level by further expanding the DystoniaNet network, in close collaboration with the ERN-RND. In line with the ERN-RND, the mission of DystoniaNet Europe is to improve care and quality of life for people with dystonia by, among other endeavors, facilitating access to specialized care, overcoming the disparity in education of medical professionals, and serving as a solid platform to foster international clinical and research collaborations. In this review, both professionals within the dystonia field and patients and caregivers representing Dystonia Europe highlight important unsolved issues and promising new strategies and the role that a European network can play in activating them.

Implicit motor imagery using laterality recognition in functional movement disorders

Functional movement disorder (FMD) presents as disabling motor symptoms that cannot be explained by organic processes. Despite the lack of lesion or known central nervous system dysfunction, distortion in sensorimotor processing in movement generation and execution is often observed. A person's capacity to judge laterality of a body part requires processing of sensorimotor information. This prospective observational study compared reaction time (RT) and accuracy (ACC) of hand laterality recognition between 30 people diagnosed with FMD and 30 age-matched healthy control participants. The association of RT and ACC with severity of FMD as measured by the Simplified Functional Movement Disorders Rating Scale (SFMDRS) was also explored. RT was on average 0.6 s slower (95% CI 0.4 - 0.8 s, p < 0.001) in patients with FMD (mean 2.2 s, standard deviation (SD) 0.5) than controls (mean 1.7 s, SD 0.3). ACC was on average 8.9% lower (95% CI -15.7 - -2.2, p = 0.01) in patients with FMD (mean 79.6%, SD 16.6) than controls (mean 88.5%, SD 8.1). When adjusted for SFMDRS using robust regression, RT was 0.3 s slower (95% CI 0.01 - 0.5, p = 0.04) in cases than in controls, but ACC was no longer different between groups. There was a moderate negative correlation between RT and ACC in FMD patients (ρ -0.58, p < 0.001 but not in controls (ρ -0.26, p = 0.17). People with FMD had significantly slower RT and lower ACC compared to the control group. These results provide new insights into underlying sensorimotor processing deficits in those with FMD.

A dimensional approach to functional movement disorders: Heresy or opportunity

Functional movement disorders (FMD) are a common and disabling neuropsychiatric condition, part of the spectrum of functional neurological/conversion disorder. FMD represent one of the most enigmatic disorders in the history of medicine. However, in the twenty years after the first report of distinctive abnormal brain activity associated with functional motor symptoms, there have been tremendous advances in the pathophysiologic understanding of these disorders. FMD can be characterized as a disorder of aberrant neurocircuitry interacting with environmental and genetic factors. These developments suggest that research on FMD could be better served by an integrative, neuroscience-based approach focused on functional domains and their neurobiological substrates. This approach has been developed in 'Research Domain Criteria' (RDoC) project, which promotes a dimensional approach to psychiatric disorders. Here, we use the RDoC conceptualization to review recent neuroscience research on FMD, focusing on the domains most relevant to these disorders. We discuss how the adoption of a similar integrative framework may facilitate the identification of the mechanisms underlying FMD and could also have potential clinical applicability.

Decade of progress in motor functional neurological disorder: continuing the momentum

Functional neurological disorder (FND) is a prevalent, disabling and costly condition at the neurology-psychiatry intersection. After being marginalised in the late 20th century, there has been renewed interest in this field. In this article, we review advances that have occurred over the past decade (2011-2020) across diagnosis, mechanisms, aetiologies, treatments and stigma in patients with motor FND (mFND, that is, functional movement disorder and functional limb weakness). In each content area, we also discuss the implications of recent advances and suggest future directions that will help continue the momentum of the past decade. In diagnosis, a major advance has been the emphasis on rule-in physical signs that are specific for hyperkinetic and hypokinetic functional motor symptoms. Mechanistically, greater importance has been given to determining 'how' functional neurological symptoms develop, highlighting roles for misdirected attention, expectation and self-agency, as well as abnormal influences of emotion/threat processing brain areas on motor control circuits. Aetiologically, while roles for adverse life experiences remain of interest in mFND, there is recognition of other aetiologic contributors, and efforts are needed to investigate links between aetiological factors and mechanisms. This decade has seen the first randomised controlled trials for physiotherapy, multidisciplinary rehabilitation and psychotherapy performed in the field, with consensus recommendations for physiotherapy, occupational therapy and outcome measures also published. Across patients, clinicians, healthcare systems and society, stigma remains a major concern. While challenges persist, a patient-centred integrated clinical neuroscience approach is primed to carry forward the momentum of the past decade into the future.

Functional motor disorders associated with other neurological diseases: Beyond the boundaries of "organic" neurology

BACKGROUND AND PURPOSE

The aims of this study were to describe the clinical manifestations of functional motor disorders (FMDs) coexisting with other neurological diseases ("comorbid FMDs"), and to compare comorbid FMDs with FMDs not overlapping with other neurological diseases ("pure FMDs").

METHODS

For this multicenter observational study, we enrolled outpatients with a definite FMD diagnosis attending 25 tertiary movement disorder centers in Italy. Each patient with FMDs underwent a detailed clinical assessment including screening for other associated neurological conditions. Group comparisons (comorbid FMDs vs. pure FMDs) were performed in order to compare demographic and clinical variables. Logistic regression models were created to estimate the adjusted odds ratios (95% confidence intervals) of comorbid FMDs (dependent variable) in relation to sociodemographic and clinical characteristics (independent variables).

RESULTS

Out of 410 FMDs, 21.7% of patients (n = 89) had comorbid FMDs. The most frequent coexisting neurological diseases were migraine, cerebrovascular disease and parkinsonism. In the majority of cases (86.5%), FMDs appeared after the diagnosis of a neurological disease. Patients with comorbid FMDs were older, and more frequently had tremor, non-neurological comorbidities, paroxysmal non-epileptic seizures, major depressive disorders, and benzodiazepine intake. Multivariate regression analysis showed that diagnosis of comorbid FMDs was more likely associated with longer time lag until the final diagnosis of FMD, presence of tremor and non-neurological comorbidities.

CONCLUSIONS

Our findings highlight the need for prompt diagnosis of FMDs, given the relatively high frequency of associated neurological and non-neurological diseases.

A framework for understanding the pathophysiology of functional neurological disorder

The symptoms of functional neurological disorder (FND) are a product of its pathophysiology. The pathophysiology of FND is reflective of dysfunction within and across different brain circuits that, in turn, affects specific constructs. In this perspective article, we briefly review five constructs that are affected in FND: emotion processing (including salience), agency, attention, interoception, and predictive processing/inference. Examples of underlying neural circuits include salience, multimodal integration, and attention networks. The symptoms of each patient can be described as a combination of dysfunction in several of these networks and related processes. While we have gained a considerable understanding of FND, there is more work to be done, including determining how pathophysiological abnormalities arise as a consequence of etiologic biopsychosocial factors. To facilitate advances in this underserved and important area, we propose a pathophysiology-focused research agenda to engage government-sponsored funding agencies and foundations.

Unfeignable biomarkers in functional neurological disorder: drifting back to Pierre Janet

This scientific commentary refers to ‘Reduced drift rate: a biomarker of impaired information processing in functional movement disorders’, by Sadnicka et al. (doi: 10.1093/brain/awz387).

Sensory Processing Difficulties in Functional Neurological Disorder: A Possible Predisposing Vulnerability?

BACKGROUND

Functional neurological disorder (FND) is a prevalent neuropsychiatric condition characterized by sensorimotor difficulties. Patients with FND at times report that sensory experiences trigger and/or exacerbate their symptoms. Sensory processing difficulties are also commonly reported in other psychiatric disorders frequently comorbid in FND, suggesting that contextualizing sensory profiles in FND within a biopsychosocial model may be clinically relevant.

OBJECTIVE

To address this literature gap, we conducted a retrospective cohort study to examine sensory processing patterns and their relationship to other neuropsychiatric characteristics in patients with FND.

METHODS

A retrospective chart review design was used to investigate sensory processing patterns, established with the Adolescent/Adult Sensory Profile self-report questionnaire, in 44 patients with FND. Univariate analyses of cross-sectional screening tests followed by multivariate linear regression analyses were performed to identify clinical factors associated with sensory processing scores in the FND cohort.

RESULTS

Compared to normative data, most patients with FND reported sensory processing tendencies toward low registration, sensory sensitivity, and sensation avoiding. In multivariate regression analyses, the presence of a lifetime anxiety disorder independently predicted elevated low registration scores, while female gender and number of current medications independently predicted increased sensory sensitivity scores. In uncorrected univariate analyses only, individuals with psychogenic nonepileptic seizures were more likely to report increased sensory sensitivity and elevated low registration.

CONCLUSION

These preliminary findings support sensory processing difficulties in some patients with FND. Prospective and large sample size studies are needed to investigate relationships between sensory processing profiles and neuropsychiatric comorbidities, FND subtypes, and treatment outcomes.