Orbito-frontal thinning together with a somatoform dissociation might be the fingerprint of PNES

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.

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.

Structural and functional changes associated with functional/dissociative seizures: A review of the literature

INTRODUCTION

The term 'functional/dissociative seizures (FDS)' refers to a paroxysmal, transient clinical manifestation that may include motor, sensory, vegetative, psychological and cognitive signs, similar to the manifestations observed in epileptic seizures. In recent years, there has been an increase of literature in the field of brain imaging research on functional neurological disorders and, more specifically, on FDS. However, most of the studies have been carried out on limited samples. We propose an update of this review work by performing a systematic review of studies performed since 2017 in the field of neuroimaging in patients with FDS.

METHODS

We conducted a systematic review of the literature using the PRISMA methodology and reproduced most of the methodological elements of the latest systematic literature review.

RESULTS

Our work over the last five years has identified 14 articles. It is still difficult to isolate a distinct structure or network specifically involved in the mechanism of FDS. However, certain structures are recurrently involved in imaging studies, notably the amygdala, the orbitofrontal cortex, and the anterior cingulate cortex.

CONCLUSION

The contribution of neuroimaging may allow a more precise explanation of the disorder for patients, avoiding the stigma frequently associated with this diagnosis. as with other 'conversion' phenomena which have traditionally been considered only as 'medically unexplained'. In the longer term and beyond a better understanding of the physiopathology of the disorder, the challenge of this neuroimaging work would be to identify specific imaging biomarkers for a diagnosis of FDS.

Amygdala subfield and prefrontal cortex abnormalities in patients with functional seizures

BACKGROUND

Functional seizures (FS) are paroxysmal episodes, resembling epileptic seizures, but without underlying epileptic abnormality. The aetiology and neuroanatomic associations are incompletely understood. Recent brain imaging data indicate cerebral changes, however, without clarifying possible pathophysiology. In the present study, we specifically investigated the neuroanatomic changes in subregions of the amygdala and hippocampus in FS.

METHODS

T1 MRI scans of 37 female patients with FS and 37 age-matched female seizure naïve controls (SNC) were analyzed retrospectively in FreeSurfer version 7.1. Seizure naïve controls included patients with depression and anxiety disorders. The analysis included whole-brain cortical thickness, subcortical volumes, and subfields of the amygdala and hippocampus. Group comparisons were carried out using multivariable linear models.

RESULTS

The FS and SNC groups did not differ in the whole hippocampus and amygdala volumes. However, patients had a significant reduction of the right lateral amygdala volume (p = 0.00041), an increase of the right central amygdala, (p = 0.037), and thinning of the left superior frontal gyrus (p = 0.024). Additional findings in patients were increased volumes of the right medial amygdala (p = 0.031), left anterior amygdala (p = 0.017), and left dentate gyrus of the hippocampus (p = 0.035).

CONCLUSIONS

The observations from the amygdala and hippocampus segmentation affirm that there are neuroanatomic associations of FS. The pattern of these changes aligned with some of the cerebral changes described in chronic stress conditions and depression. The pattern of detected changes further study, and may, after validation, provide biomarkers for diagnosis and treatment.

Morphometric correlates in patients with functional seizures with and without comorbid epilepsy

OBJECTIVE

Functional seizures (FS) or psychogenic, non-epileptic seizures (PNES) are episodic alterations of behaviour with similar semiology to epileptic seizures but which are not caused by epileptic brain activity. Epilepsy patients show a high risk in developing FS; therefore, the purpose of this study is to examine morphometric correlates in patients with FS as well as in epilepsy patients with FS by comparing them separately to healthy controls (HC).

METHODS

Twenty-one clinical three-dimensional (3D) T1-magnetic resonance imaging (MRI) scans of patients with FS (FS group) and 15 patients with FS and epilepsy (EFS group) were retrospectively compared with one control group of 21 age- and gender-matched HC. Two separate general linear model analyses were conducted via FreeSurfer version 6.0.

RESULTS

The study population consisted of 21 FS patients (66.7% females, n = 14) with a median age at the time of the scan of 24 years (range 17-44 years); 15 EFS patients (80% females, n = 12) with a median age at the time of the scan of 27 years (range 16-43 years); and 21 healthy subjects (66.7% females, n = 14) with a median age at the time of the scan of 24 years (range 19-38 years). Both patient groups showed an increased Cth in the right prefrontal lobe: in the FS group in the right superior frontal, rostral middle frontal gyri and the right orbitofrontal cortex and, in the EFS group, in the right superior frontal gyrus and the right orbitofrontal cortex. Decreases in Cth were present in the right lateral occipital lobe in the FS group, while also in both hemispheres in the EFS group, namely the left paracentral, superior frontal, caudal middle frontal, lateral occipital and right superior frontal gyri. Neither group showed changes in curvature.

CONCLUSION

These results suggest alterations in regions of emotional processing and executive control in patients with FS regardless of the presence of epilepsy.

Dissociation and its biological and clinical associations in functional neurological disorder: systematic review and meta-analysis

BACKGROUND

Studies have reported elevated rates of dissociative symptoms and comorbid dissociative disorders in functional neurological disorder (FND); however, a comprehensive review is lacking.

AIMS

To systematically review the severity of dissociative symptoms and prevalence of comorbid dissociative disorders in FND and summarise their biological and clinical associations.

METHOD

We searched Embase, PsycInfo and MEDLINE up to June 2021, combining terms for FND and dissociation. Studies were eligible if reporting dissociative symptom scores or rates of comorbid dissociative disorder in FND samples. Risk of bias was appraised using modified Newcastle-Ottawa criteria. The findings were synthesised qualitatively and dissociative symptom scores were included in a meta-analysis (PROSPERO CRD42020173263).

RESULTS

Seventy-five studies were eligible (FND n = 3940; control n = 3073), most commonly prospective case-control studies (k = 54). Dissociative disorders were frequently comorbid in FND. Psychoform dissociation was elevated in FND compared with healthy (g = 0.90, 95% CI 0.66-1.14, I² = 70%) and neurological controls (g = 0.56, 95% CI 0.19-0.92, I² = 67%). Greater psychoform dissociation was observed in FND samples with seizure symptoms versus healthy controls (g = 0.94, 95% CI 0.65-1.22, I² = 42%) and FND samples with motor symptoms (g = 0.40, 95% CI -0.18 to 1.00, I² = 54%). Somatoform dissociation was elevated in FND versus healthy controls (g = 1.80, 95% CI 1.25-2.34, I² = 75%). Dissociation in FND was associated with more severe functional symptoms, worse quality of life and brain alterations.

CONCLUSIONS

Our findings highlight the potential clinical utility of assessing patients with FND for dissociative symptomatology. However, fewer studies investigated FND samples with motor symptoms and heterogeneity between studies and risk of bias were high. Rigorous investigation of the prevalence, features and mechanistic relevance of dissociation in FND is needed.

Linking gene expression patterns and brain morphometry to trauma and symptom severity in patients with functional seizures

Within stress-diathesis models, adverse life experiences (ALEs) increase the susceptibility to functional neurological symptoms through neuroplasticity effects. We aimed to characterize potential genetic influences on this relationship in 20 patients with functional seizures. Questionnaires, structural MRIs and Allen Human Brain Atlas gene expression information were used to probe the intersection of symptom severity (Somatoform Dissociation Questionnaire, SDQ-20), ALE burden, and gray matter volumes. SDQ-20 scores positively correlated with sexual trauma, emotional neglect, and threat to life experiences. Higher SDQ-20 scores related to lower bilateral insula, left orbitofrontal, right amygdala, and perigenual/posterior cingulate volumes. Higher sexual trauma burden correlated with lower right posterior insula and putamen volumes; higher emotional neglect related to lower bilateral insula/right amygdala volumes. Findings in left insula/ventral precentral gyrus (SDQ-20), right insula/putamen (sexual trauma), and right amygdala (emotional neglect) held when controlling for comorbid psychopathology. At the intersection of symptom severity and sexual trauma volumetric findings, genes overrepresented in adrenergic, serotonergic, and oxytocin receptor signaling as well as in cortical and amygdala development were spatially correlated. In conclusion, ALEs and symptom severity were associated with gray matter volumes in cingulo-insular and amygdala areas, spatially overlapping with expression patterns of genes involved in stress-related signaling and neurodevelopment.

Cortical thickness in default mode network hubs correlates with clinical features of dissociative seizures

BACKGROUND

Dissociative seizures (DS) are a common subtype of functional neurological disorder (FND) with an incompletely understood pathophysiology. Here, gray matter variations and their relationship to clinical features were investigated.

METHODS

Forty-eight patients with DS without neurological comorbidities and 43 matched clinical control patients with syncope with structural brain MRIs were identified retrospectively. FreeSurfer-based cortical thickness and FSL FIRST-based subcortical volumes were used for quantitative analyses, and all findings were age and sex adjusted, and corrected for multiple comparisons.

RESULTS

Groups were not statistically different in cortical thickness or subcortical volumes. For patients with DS, illness duration was inversely correlated with cortical thickness of left-sided anterior and posterior cortical midline structures (perigenual/dorsal anterior cingulate cortex, superior parietal cortex, precuneus), and clusters at the left temporoparietal junction (supramarginal gyrus, postcentral gyrus, superior temporal gyrus), left postcentral gyrus, and right pericalcarine cortex. Dissociative seizure duration was inversely correlated with cortical thickness in the left perigenual anterior cingulate cortex, superior/middle frontal gyri, precentral gyrus and lateral occipital cortex, along with the right isthmus-cingulate and posterior-cingulate, middle temporal gyrus, and precuneus. Seizure frequency did not show any significant correlations.

CONCLUSIONS

In patients with DS, illness duration inversely correlated with cortical thickness of left-sided default mode network cortical hubs, while seizure duration correlated with left frontopolar and right posteromedial areas, among others. Etiological factors contributing to neuroanatomical variations in areas related to self-referential processing in patients with DS require more research inquiry.