Abnormalities of the Descending Inhibitory Nociceptive Pathway in Functional Motor Disorders.

BACKGROUND: Pain is a common disabling non-motor symptom affecting patients with functional motor disorders (FMD). OBJECTIVE: We aimed to explore ascending and descending nociceptive pathways with laser evoked potentials (LEPs) in FMD. METHODS: We studied a "bottom-up and top-down" noxious paradigm applying a conditioned pain modulation (CPM) protocol and recorded N2/P2 amplitude in 21 FMD and 20 controls following stimulation of both right arm and leg at baseline (BS) (bottom-up), during heterotopic noxious conditioning stimulation (HNCS) with ice test (top-down) and post-HNCS. RESULTS: We found a normal ascending pathway, but reduced CPM response (lower reduction of the N2/P2 amplitude) in FMD patients, by stimulating both upper and lower limbs. The N2/P2 amplitude ratio*100 (between the HNCS and BS) was significantly higher in patients with FMD than HC. CONCLUSIONS: Our results suggest that pain in FMD possibly reflects a descending pain inhibitory control impairment, therefore, providing a novel venue to explore the pathophysiology of pain in FMD. © 2024 International Parkinson and Movement Disorder Society.

Unraveling the mechanisms of high-level gait control in functional gait disorders.

Functional gait disorders (FGDs) are a disabling subset of Functional Neurological Disorders in which presenting symptoms arise from altered high-level motor control. The dual-task paradigm can be used to investigate mechanisms of high-level gait control. The study aimed to determine the objective measures of gait that best discriminate between individuals with FGDs and healthy controls and the relationship with disease severity and duration. High-level spatiotemporal gait outcomes were analyzed in 87 patients with FGDs (79.3% women, average age 41.9±14.7 years) and 48 healthy controls (60.4% women, average age 41.9±15.7 years) on single and motor, cognitive, and visual-fixation dual tasks. The area under the curve (AUC) from the receiver operator characteristic plot and the dual-task effect (DTE) were calculated for each measure. Dual-task interference on the top single-task gait characteristics was determined by two-way repeated measures ANOVA. Stride time variability and its standard deviation (SD) failed to discriminate between the two groups in single and dual-task conditions (AUC<0.80 for all). Significant group x task interactions were observed for swing time SD and stride time on the cognitive dual tasks (p<0.035 for all). Longer disease duration was associated with poor gait performance and unsteadiness in motor and cognitive DTE (p<0.003) but improvement in stride length and swing time on the visual dual tasks (p<0.041). Our preliminary findings shed light on measures of gait automaticity as a diagnostic and prognostic gait biomarker and underline the importance of early diagnosis and management in individuals with FGDs.

Do demographic and clinical features and comorbidities affect the risk of spread to an additional body site in functional motor disorders?

The aim of this study is to assess changes in the body distribution and the semeiology of functional motor disorder (FMD) in patients who reported only one or more than one body site affected at FMD onset. Data were obtained from the Italian Registry of Functional Motor Disorders, which included patients with a diagnosis of clinically definite FMDs. The relationship between FMD features and spread to other body sites was estimated by multivariate Cox regression analysis. We identified 201 (49%) patients who reported only one body site affected at FMD onset and 209 (51%) who reported multiple body sites affected at onset. FMD spread from the initial site to another site in 43/201 (21.4%) patients over 5.7 ± 7.1 years in those with only one site affected at FMD onset; FMD spread to an another body site in 29/209 (13.8%) over 5.5 ± 6.5 years. The spread of FMD was associated with non-motor functional symptoms and psychiatric comorbidities only in the patients with one body site affected at FMD onset. Our findings provide novel insight into the natural history of FMD. The number of body sites affected at onset does not seem to have a consistent influence on the risk of spread. Furthermore, our findings suggest that psychiatric comorbidities and non-motor functional symptoms may predict the spread of FMD symptoms, at least in patients with one body site affected at onset.

Shoulder-Touch test to reveal incongruencies in persons with functional motor disorders.

BACKGROUND AND PURPOSE: Clinical experience suggests that many patients with functional motor disorders (FMD), despite reporting severe balance problems, typically do not fall frequently. This discrepancy may hint towards a functional component. Here, we explored the role of the Shoulder-Touch test, which features a light touch on the patient's shoulders, to reveal a possible functional etiology of postural instability. METHODS: We enrolled consecutive outpatients with a definite diagnosis of FMD. Patients with Parkinson's disease (PD) or progressive supranuclear palsy (PSP) with postural instability served as controls. Each patient underwent a clinical evaluation including testing for postural instability using the retropulsion test. Patients with an abnormal retropulsion test (score ≥ 1) also received a light touch on their shoulders to explore the presence (S-Touch+) or absence (S-Touch-) of an incongruent, exaggerated postural response, defined as taking three or more steps to recover or a fall if not caught by the examiner. RESULTS: From a total sample of 52 FMD patients, 48 patients were recruited. Twenty-five patients (52%) had an abnormal retropulsion test. Twelve of these 25 patients (48%) had an S-Touch+, either because of need to take two or more steps (n = 4) or a fall if not caught by the examiner (n = 8). None of the 23 PD/PSP patients manifested S-Touch+. The sensitivity of the S-Touch test was 48%, whereas its specificity was 100%. CONCLUSION: The S-Touch test has a high specificity, albeit with a modest sensitivity, to reveal a functional etiology of postural instability in persons with FMD.

Hedonicity in functional motor disorders: a chemosensory study assessing taste.

The aim of this study was to explore hedonicity to basic tastes in patients with functional motor disorders (FMDs) that are often associated with impairment in emotional processing. We recruited 20 FMD patients and 24 healthy subjects, matched for age and sex. Subjects were asked to rate the hedonic sensation (i.e., pleasant, neutral, and unpleasant) on a - 10 to +10 scale to the four basic tastes (sweet, sour, salty, and bitter) at different concentrations, and neutral stimuli (i.e., no taste stimulation) by means of the Taste Strips Test. Anxiety, depression, and alexithymia were assessed. FMD patients rated the highest concentration of sweet taste (6.7 ± 2.6) as significantly more pleasant than controls (4.7 ± 2.5, p = 0.03), and the neutral stimuli significantly more unpleasant (patients: - 0.7 ± 0.4, controls: 0.1 ± 0.4, p = 0.013). Hedonic ratings were not correlated to anxiety, depression, or alexithymia scores. Hedonic response to taste is altered in FMD patients. This preliminary finding might result from abnormal interaction between sensory processing and emotional valence.

Functional Motor Symptoms in Parkinson's Disease and Functional Parkinsonism: A Systematic Review.

OBJECTIVE: Whereas functional symptoms are common in Parkinson's disease (PD), a parkinsonian syndrome may occasionally reflect a pure functional disorder (also named functional parkinsonism [FP]). This review aimed to decipher these entities to clarify the link between functional manifestations and PD. METHODS: Following the PRISMA guidelines, the authors performed a systematic literature search of the PubMed and Science Direct databases for the period 1988 to December 2018 to identify studies of patients with either FP or PD associated with functional neurological symptoms. RESULTS: From the 844 articles screened, 22 were retained, including 12 studies of functional neurological symptoms in PD and 16 studies of FP. The studies of functional symptoms in PD included 121 patients-57% were women, and the mean age was 61.3 years. Psychiatric history (mostly depression) and exposure to triggering stressors were frequent: 60% and 82.5%, respectively. The most common symptom was tremor (33.8%), most often located on the side most affected by PD (50%). Studies of FP included a total of 120 patients-62% were women, and the mean age was 50.7 years. The first FP symptoms appeared on average 5 years before diagnosis, with an abrupt onset in half the cases; 67.6% had a psychiatric history, and 46.8% were exposed to triggering stressors, such as physical injury, stress at work, or loss of family or friends. CONCLUSIONS: Findings suggest a possible relationship between PD and FP. Clinicians should keep in mind the possibility of functional symptoms in PD patients.

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.

Elderly Onset of Functional Motor Disorders: Clinical Correlates from the Italian Registry.

BACKGROUND: Functional motor disorders (FMD) are a frequent neurological condition affecting patients with movement disorders. Commonly described in younger adults, their manifestation can be also associated to an elderly onset. OBJECTIVE: To assess the prevalence and describe the clinical manifestations of FMD with elderly and younger onset and their relationship with demographical and clinical variables. METHODS: We recruited patients with a "clinically definite" diagnosis of FMD from the Italian Registry of FMD. Patients underwent extensive clinical assessments. For elderly onset, we set a chronological cut-off at 65 years or older according to WHO definition. Multivariate regression models were implemented to estimate adjusted odds ratio of elderly FMD onset related to clinical characteristics. RESULTS: Among the 410 patients, 34 (8.2%) experienced elderly-onset FMD, with a mean age at onset of 70.9 years. The most common phenotype was tremor (47.1%), followed by gait disorders, weakness, and dystonia (29.4%, 23.5%, 14.7%, respectively). Eleven elderly patients had a combined phenomenology: 9 exhibited two phenotypes, 2 had three phenotypes. Weakness was isolated in 3/8 patients and combined with another phenotype in 5/8, manifesting as paraplegia (n = 4); upper limb diplegia (n = 2), hemiparesis/hemiplegia (n = 1), and tetraparesis/tetraplegia (n= 1). Non-motor and other functional neurological disorders occurred more frequently in the younger group (89.1%) than the elderly (73.5%). Neurological and non-neurological comorbidities were more prevalent in the elderly group (82.4%) as opposed to the younger (32.7%). In a multivariate regression analysis, elderly-onset FMD was significantly associated with neurological comorbidities, including parkinsonism (OR 6.73) and cerebrovascular diseases (OR 5.48). CONCLUSIONS: These results highlight the importance of achieving an accurate diagnosis of FMD in the elderly, as it is crucial for effectively managing FMD symptoms and addressing neurological comorbidities.

Dual tasking affects gait performance but not automaticity in functional gait disorders: A new diagnostic biomarker.

INTRODUCTION: Functional gait disorders (FGDs) are disabling symptoms of Functional Motor Disorders. Clinical observations show improvement with distraction suggesting an association with higher-level control mechanisms. Dual tasking is a valuable tool for exploring the interplay between gait and cognition. Our research question was: how do different dual task paradigms shape spatio-temporal gait parameters in FGDs?. METHODS: In all, 29 patients with FGDs (age 43.48 ± 15.42 years; female 75%) and 49 healthy controls (age 43.33 ± 15.41 years; female 62%) underwent spatio-temporal gait analysis during a single task and during performance on a motor, a cognitive, and a visual-fixation dual-task. The dual-task effect was a measure of interference of the concurrent task on gait speed, stride length (a measure of gait performance), and stride time variability (a measure of automaticity and steadiness). RESULTS: Overall lower gait speed, shorter stride length, and higher stride time variability were noted in FGDs compared to healthy controls (for all, p < 0.019). The was a significant effect of group and Task × Group interaction for the dual-task effect on gait speed (p = 0.023) and stride length (p = 0.01) but not for stride time variability. CONCLUSION: Poorer gait performance and less automaticity and steadiness were noted in FGDs. However, dual tasking affected gait performance but, unlike different neurological diseases, not automaticity and steadiness compared to controls. Our findings shed light on higher-level gait control mechanisms in FGDs and suggest stride time variability could be a diagnostic and prognostic biomarker.

Neurofilament light chain: a promising diagnostic biomarker for functional motor disorders.

OBJECTIVE: Functional motor disorders (FMDs) are disabling neurological conditions characterized by abnormal movements which are inconsistent and incongruent with recognized neurological diseases. Aim of this study is to investigate whether FMDs are related to structural axonal damage. METHODS: Consecutive patients with a definite diagnosis of FMD with no other neurological/psychiatric comorbidities (pure FMDs) and age-matched healthy controls (HCs) were recruited in a tertiary center and demographic/clinical data were collected. Serum neurofilament light chain (NfL) assessment was performed with ultrasensitive paramagnetic bead-based enzyme-linked immunosorbent assay. RESULTS: 34 patients with FMDs and 34 HCs were included. NfL levels were similar (p = 0.135) in FMDs (median 8.3 pg/mL, range 2-33.7) and HCs (median 6.1 pg/mL, range 2.7-15.6). The area under curve (0.606, 95% CI 0.468-0.743) confirmed that NfL concentration was not different in the two groups. NfL values were similar in patients with paroxysmal vs persistent disease course (p = 0.301), and isolated vs combined symptoms (p = 0.537). NfL levels were associated with age (p < 0.0001), but not with disease duration (p = 0.425), number of CNS acting drugs (p = 0.850), or clinical features (p = 0.983). DISCUSSION: Our preliminary data show that NfL levels are similar in patients with FMDs and HCs, indicating the lack of neuroaxonal damage. These results have relevant pathogenic and clinical implications and suggest that serum NfL may be a promising diagnostic biomarker, potentially useful to differentiate functional vs structural neurological disorders.

Physical Rehabilitation of Motor Functional Neurological Disorders: A Narrative Review.

Functional Neurological Disorders (FNDs) are one of the most common and disabling neurological disorders, affecting approximately 10-30% of patients in neurology clinics. FNDs manifest as a range of motor, sensory, and cognitive symptoms that are not explained by organic disease. This narrative review aims to assess the current state of knowledge in physical-based rehabilitation for motor/movement FNDs in the adult population, with the goal of improving research and medical care for this patient population. To ensure optimal outcomes for patients, it is critical to consider several domains pertaining to FNDs, including which field of discipline they should belong to, how to investigate and test, methods for rating outcome measures, and optimal courses of treatment. In the past, FNDs were primarily treated with psychiatric and psychological interventions. However, recent literature supports the inclusion of physical rehabilitation in the treatment of FNDs. Specifically, physical-based approaches tailored to FNDs have shown promising results. This review utilized a comprehensive search of multiple databases and inclusion criteria to identify relevant studies.

Triggers in functional motor disorder: a clinical feature distinct from precipitating factors.

BACKGROUND AND OBJECTIVE: People with functional motor disorder (FMD) report triggers-sensory or motor-induced stimuli that exacerbate or initiate paroxysmal occurrences of their movement disorder. These are a distinct phenomenon from precipitating factors occurring at the initial onset of the disorder. We aimed to assess triggers in FMD and understand their relevance to paroxysmal variability often seen in FMD. METHODS: We enrolled consecutive outpatients with a definite diagnosis of FMD. Each patient underwent a detailed clinical evaluation also including the presence of trigger factors and video-recordings both during neurological examination and physiotherapy treatment. Patients were classified as having "triggers" (T-FMD) or "not having triggers" (NoT-FMD) as well as "paroxysmal" compared to "persistent with paroxysmal variability". RESULTS: The study sample was 100 patients (82% female) with FMD; the mean age at onset was 41 years. Triggers were observed in 88% of patients and in 65 of these the FMD was pure paroxysmal. The most common triggers were movement or physical exercise, followed by emotional, visual, touch, and auditory stimuli; 39 (44%) were isolated and 49 (56%) were combined triggers. Among the T-FMD patients, FMD were paroxysmal in 74% (n = 65) and persistent with paroxysmal variability in 26% (n = 23). The T-FMD patients were younger (p = 0.016) and had a gait disorder (p = 0.035) more frequently than the NoT-FMD patients. DISCUSSION: Triggers are frequent in FMD and may have diverse overlapping clinical presentations. In this sample, FMD was most often paroxysmal, suggesting the value of noting triggers as clinical clues in the diagnosis and rehabilitation of FMD.

Data-driven clustering of combined Functional Motor Disorders based on the Italian registry.

Introduction: Functional Motor Disorders (FMDs) represent nosological entities with no clear phenotypic characterization, especially in patients with multiple (combined FMDs) motor manifestations. A data-driven approach using cluster analysis of clinical data has been proposed as an analytic method to obtain non-hierarchical unbiased classifications. The study aimed to identify clinical subtypes of combined FMDs using a data-driven approach to overcome possible limits related to "a priori" classifications and clinical overlapping. Methods: Data were obtained by the Italian Registry of Functional Motor Disorders. Patients identified with multiple or "combined" FMDs by standardized clinical assessments were selected to be analyzed. Non-hierarchical cluster analysis was performed based on FMDs phenomenology. Multivariate analysis was then performed after adjustment for principal confounding variables. Results: From a study population of n = 410 subjects with FMDs, we selected n = 188 subjects [women: 133 (70.7%); age: 47.9 ± 14.4 years; disease duration: 6.4 ± 7.7 years] presenting combined FMDs to be analyzed. Based on motor phenotype, two independent clusters were identified: Cluster C1 (n = 82; 43.6%) and Cluster C2 (n = 106; 56.4%). Cluster C1 was characterized by functional tremor plus parkinsonism as the main clinical phenotype. Cluster C2 mainly included subjects with functional weakness. Cluster C1 included older subjects suffering from anxiety who were more treated with botulinum toxin and antiepileptics. Cluster C2 included younger subjects referring to different associated symptoms, such as pain, headache, and visual disturbances, who were more treated with antidepressants. Conclusion: Using a data-driven approach of clinical data from the Italian registry, we differentiated clinical subtypes among combined FMDs to be validated by prospective studies.

Motor dual task with eyes closed improves postural control in patients with functional motor disorders: A posturographic study.

BACKGROUND: Functional motor disorders (FMD) are highly disabling neurological conditions in which postural control deficits increase the risk of falls and disability in performing daily living activities. Scattered evidence suggests that such disturbances may depend on abnormal attentional focus and might improve with distraction. RESEARCH QUESTION: How do motor and cognitive dual tasks performed under two different sensory conditions shape postural control in patients with FMD. METHODS: This posturographic study involved 30 patients with FMD (age, 45.20 ± 14.57 years) and 30 healthy controls (age, 41.20 ± 16.50 years). Postural parameters were measured with eyes open, and eyes closed in quiet stance (single task) and on a motor dual task (m-DT) and a calculation (cognitive) dual task (c-DT). The dual task effect (DTE, expressed in percentage) on motor and cognitive performance was calculated for sway area, length of Center of Pressure (CoP), and velocity of CoP displacement. RESULTS: There was a statistically significant three-way interaction between task, condition, and group for the DTE on sway area (p = 0.03). The mean sway area DTE on the motor task in the eyes-closed condition was increased by 70.4 % in the healthy controls, while it was decreased by 1% in the patient group (p = 0.003). No significant three-way interaction was observed for the DTE on length of CoP and velocity of CoP displacement. SIGNIFICANCE: This study provides novel preliminary evidence for the benefit of a simple motor dual task in the eyes closed condition as a way to improve postural control in patients with FMD. These findings are relevant for the management of postural control disorders in patients with FMD.

Movement perception of the tonic vibration reflex is abnormal in functional limb weakness.

INTRODUCTION: We tested the hypothesis that functional limb weakness is associated with possible dysfunction of the central processing of proprioceptive information, by evaluating the amount of tonic vibration reflex (TVR) and the perception of the TVR movement. METHODS: The study sample was 20 patients with functional weakness of the lower and/or the upper limbs and 25 healthy controls; delivery of 92-Hz transcutaneous vibration of the biceps brachii tendon of the unrestrained arm stimulated predominantly the muscle spindle afferent and elicited elbow flexion (tonic vibration reflex, TVR). Blindfolded participants had to match the final position of the vibrated arm with their contralateral tracking arm. The TVR and perception of the TVR movement were measured as angle movements of the vibrated arm and the tracking arm, respectively. RESULTS: The magnitude of the TVR of the vibrated arm and movement perception of the TVR of the tracking arm were significantly reduced in the patients compared to the controls. No correlation was found between magnitude of the TVR and perception of the TVR movement, suggesting that the abnormalities were independent of each other. Moreover, the abnormalities did not differ between the patients with/without bilateral upper limb involvement or between the affected and the unaffected side in patients with unilateral impairment, suggesting that the observed deficits are independent of motor impairment. CONCLUSIONS: Proprioceptive dysfunction may underlie alterations in body movement and in sense of agency in such patients and may play a role in the pathophysiology of functional limb weakness.

Motor and non-motor outcomes after a rehabilitation program for patients with Functional Motor Disorders: A prospective, observational cohort study.

BACKGROUND: Rehabilitation has proven effective in improving motor symptoms (i.e., weakness, tremor, gait and balance disorders) in patients with Functional Motor Disorders (FMDs). Its effects on non-motor symptoms (NMSs) such as fatigue, pain, depression, anxiety and alexithymia, have not been explored yet. OBJECTIVE: To explore the effects of a validated inpatient 5-day rehabilitation program, followed by a home-based self-management plan on functional motor symptoms, NMSs, self-rated perception of change, and quality of life (QoL). METHODS: 33 FMD patients were enrolled. Measures for motor symptoms and NMSs were primary outcomes. Secondary outcomes included measures of self-perception of change and QoL. Patients were evaluated pre-treatment (T0), post-treatment (T1), and 3-month follow-up (T2). RESULTS: There was an overall significant decrease in functional motor symptoms, general, physical, and reduced-activity fatigue (for all, p < 0.001). Post hoc comparison showed significant improvements at T1, whereas effects remained significant at T2 for motor symptoms and physical fatigue. Gait and balance, alexithymia, and physical functioning (QoL) significantly improved at T2. More than 50% of patients reported marked improvement at T1 and T2. CONCLUSIONS: Our study suggests the benefits of rehabilitation and self-management plan on functional motor symptoms and physical fatigue in the medium-term. More actions are needed for the management of pain and other distressing NMSs in FMDs.

A single-center series of 482 patients with functional motor disorders.

Functional motor disorders (FMD) are common and disabling. They are known to predominantly affect women and young to middle-aged patients, although they also occur during childhood or in the elderly. Demographic and clinical characteristics of patients with FMD are poorly known, since large series of consecutive patients are scarce. METHODS: In a chart review study, we retrospectively abstracted data from consecutive FMD patients who were referred to the Neurophysiology Department of the Salpêtrière University Hospital between 2008 and 2016 for treatment with repeated transcranial magnetic stimulation. RESULTS: 482 patients were included. Most patients were women (73.7%). Median age at symptoms onset was 35.5 years and symptoms were mostly characterized by acute (47.3%) or subacute (46%) onset. Only 23% of patients were active workers, while 58.3% were unemployed because of FMD. Half of the patients had functional motor weakness (n = 241) whereas the other half had movement disorders (n = 241), mainly with tremor (21.1%) or dystonia (20.5%). Among all patients, 66.4% had psychiatric comorbidity and 82.6% reported a history of trauma in the 6 months before symptoms onset. No difference was found in age or gender according to clinical phenotypes. CONCLUSION: This large series will contribute to better characterize FMDs.

Raised visual contrast thresholds with intact attention and metacognition in functional motor disorder.

Functional motor disorders (FMDs) are distinguished by signs that lack congruence with recognised patterns of organic disease and show inconsistency over time. Their pathophysiology is poorly understood, but there is evidence that irregularities in perceptual and cognitive processing lie at the heart of these conditions. Here, we draw on a predictive coding account of functional neurological disorders to study perceptual decision-making in three groups: 20 patients with FMDs (14 with functional movements and 6 with functional weakness), 20 with phenotypically-matched organic motor disorders, and 20 age-matched healthy controls. We examine four cognitive domains with putative roles in FMD pathogenesis: attention, expectations, sensory processing (perceptual sensitivity), and metacognition (introspective evaluation of performance). We augmented a dual-task paradigm, manipulating the visual contrast required for target detection to examine these domains in one design. With sensory input (stimulus contrast) psychometrically adjusted to staircase target detection at a fixed level for all groups, the FMD group exhibited statistically equivalent attentional, expectational and metacognitive processing to healthy controls. However, we demonstrate Bayesian evidence and a frequentist trend that FMD patients require higher visual contrast than controls to maintain the same detection sensitivity (BF10 = 8.1, pholm = .066). This was statistically equivalent to the visual contrast required by the organic group, and unlikely to be accounted for by medication use or comorbid psychopathology. The organic group showed differences in processing of attention and expectations for target detection that were not observed in either healthy controls or the functional group. The distinctive behavioural profile of FMDs may arise from abnormalities in basic sensory processing, while higher attentional, expectational and metacognitive mechanisms remain intact. Conceptualising functional neurological disorders under a predictive coding account may consolidate and refine existing pathophysiological theories about them.

Shared demographics and comorbidities in different functional motor disorders.

INTRODUCTION: Functional motor disorders are often delineated according to the dominant motor symptom. In a large cohort, we aimed to find if there were differences in demographics, mode of onset, pain, fatigue, depression and anxiety and levels of physical functioning, quality of life and social adjustment between patients with different dominant motor symptoms. METHODS: Baseline data from the Self-Help and Education on the Internet for Functional Motor Disorders Trial was used. Patients were divided into dominant motor symptom groups based on the diagnosis of the referring neurologist. Data on the above topics were collected by means of an online questionnaire and compared between groups using parametric and nonparametric statistics. RESULTS: In 160 patients a dominant motor symptom could be determined, 31 had tremor, 45 myoclonus, 23 dystonia, 30 paresis, 31 gait disorder. No statistical differences between groups were detected for demographics, mode of onset and severity of pain, fatigue, depression and anxiety. Physical functioning was worse in the gait disorder group (median 20, IQR 25) compared to tremor (50 (55), p = 0.002) and myoclonus (50 (52), p = 0.001). Work and social adjustment was less impaired in the myoclonus group (median 20, IQR 18) compared to gait disorder (median 30, IQR18, p < 0.001) and paresis (28, IQR 10, p = 0.001). Self-report showed large overlap in motor symptoms. CONCLUSION: No differences were detected between groups of functional motor symptoms, regarding demographics, mode of onset, depression, anxiety, pain and fatigue. The large overlap in symptoms contributes to the hypothesis of shared underlying mechanisms of functional motor disorders.