Introduction: We aimed to examine susceptibility to dissociation and the impact of dissociation on interoceptive processing in individuals with functional neurological disorder (FND). We hypothesised that dissociative states would be elevated and interoceptive accuracy and awareness impaired at baseline in people with FND, and that such differences would be exacerbated following acute dissociation. Methods: Nineteen adults with FND were compared to 20 healthy controls. A modified heartbeat tracking task measured interoceptive accuracy and awareness (confidence) before and after a validated dissociation induction procedure. An exteroceptive processing control task was included. Mann-Whitney tests and r-values (effect size) were computed for between-group comparisons. Results: The FND group displayed elevated dissociation at baseline (p = 0.001, r = 0.528) compared to controls which increased following dissociation-induction (p < 0.001, r = 0.663). Interoceptive accuracy did not differ between groups at baseline (p = 0.967, r = 0.009); however, the FND group had lower accuracy scores postinduction (p = 0.021, r = 0.379). A negative correlation (trend) between change scores for dissociation and interoceptive accuracy was noted (r s = −0.411, p = 0.057). Confidence ratings on interoceptive and exteroceptive processing tasks were lower in the FND group (p-values < 0.05 or <0.01, r-values 0.331-0.489). Conclusions: Individuals with FND experienced greater susceptibility to dissociation, metacognitive deficits and impaired interoceptive accuracy than controls after acute dissociation.

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.

Objective/aimsInteroceptive differences have been proposed as an aetiological factor in functional neurological disorder (FND) but there is limited supportive evidence. Previous studies are few, have mixed findings and assessed only (objective) interoceptive accuracy, but not (metacognitive) interoceptive awareness. The aim of this study was to explore interoception in FND in greater detail, by assessing interoceptive accuracy and awareness in individuals with a range of FND presentations. As dissociative symptoms (e.g., depersonalisation, derealisation) are common in FND and could influence interoception, we sought to examine the effects of induced acute dissociation on interoception. We hypothesised that interoceptive accuracy/awareness would be impaired at baseline in FND relative to healthy controls, but that the differences would be exacerbated following dissociation induction.MethodsTwenty adults with FND were recruited from online FND support groups. Diagnosis was confirmed by medical documentation from a relevant healthcare professional. The FND group was compared to a group of 20 healthy controls recruited from online community groups. A modified heart-beat tracking task measured interoceptive accuracy (correct detection of heart beats) and awareness (confidence judgements). A control task involved counting visually presented geometric shapes. Both tasks were completed before and after a validated dissociation induction procedure (mirror-gazing).ResultsThe FND group reported elevated dissociation at baseline relative to controls (p<0.01) but this difference was larger following mirror-gazing (p<0.001). Interoceptive accuracy did not differ significantly between groups at baseline; however, the FND group had significantly lower accuracy scores following mirror-gazing (p<0.05). There was no effect of group on shape counting accuracy at either timepoint. Confidence ratings on the interoception and shape counting tasks were significantly lower at both timepoints in the FND group relative to controls (all p-values <0.05 or <0.01).ConclusionsIndividuals with FND reported elevated dissociation both before and after a dissociation induction procedure, although this was exacerbated post-dissociation induction. In contrast, interoceptive accuracy was unimpaired at baseline, but impaired following dissociation induction, relative to controls. The FND group showed reduced metacognitive awareness for detection of bodily states and external (visual) stimuli. Future research should better determine the nature of interoceptive deficits in FND and assess the impact of dissociation on a range of cognitive and affective processes relevant to the disorder.

Objectives/AimsDissociation is a potential mechanism in FND. Although scientific studies report elevated rates of dissociative symptoms in FND, a systematic assessment of the biological and clinical correlates of dissociation in FND is lacking. We aimed to systematically review the current evidence describing dissociative symptoms and disorders in functional neurological disorder (FND), and additionally conduct a meta-analysis of dissociative symptom severity in FND. We also aimed to synthesise the existing data on biological and clinical correlates of dissociation in FND.MethodsWe systematically searched Embase, PsycINFO, and Medline, combining terms for FND and dissociation. Studies were eligible for inclusion if reporting on dissociative symptom scale scores or rates of dissociative disorder in FND samples. Studies were appraised for methodological quality using modified Newcastle-Ottawa criteria. Findings pertaining to dissociative symptoms or disorders, as well as biological and clinical correlates of dissociation in FND samples, were synthesised qualitatively. Dissociative symptom scores were included in a meta-analysis using random and mixed effects models.ResultsTwo-thousand and eighty-eight records were screened and seventy-nine studies were included in the final review. Dissociative symptoms were elevated in FND. The meta-analysis demonstrated a significant elevation in dissociation in FND samples relative to neurological and healthy controls, but not psychiatric controls. Dissociative disorders were frequently co-morbid in FND samples. Psychoform (cognitive) dissociation was more prominent in FND-seizures, whereas somatoform (physical) dissociation tended to be more prominent in FND-motor symptom samples. Dissociation was associated with FND symptom severity or frequency, general psychopathology, and reduced quality of life. Biological correlates of elevated dissociation included structural and functional brain alterations in regions that have previously been implicated in FND, such as the anterior cingulate cortex.ConclusionsDissociative symptoms and disorders are common in FND, and different FND subgroups appear to endorse varying degrees of psychoform or somatoform dissociation. Presence of dissociative symptoms in FND is associated with adverse clinical features; there is therefore a clinical need to assess patients with FND for dissociative symptomatology and to address these symptoms during treatment. Future research should examine dissociation further in different FND subgroups, using measures that distinguish between different types of dissociation, alongside measures of underlying pathophysiology.