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34 A systematic review comparing symptomaticity and markers of interoception in patients with functional seizures, and dual diagnosis epilepsy with functional seizures
  1. Kandasamy Rohan1,
  2. May Felix2,
  3. Yogarajah Mahinda1
  1. 1National Hospital of Neurology and Neurosurgery
  2. 2Bristol Royal Infirmary


Introduction/Objectives Comorbid/dual diagnosis (DD) epilepsy (ES) and functional seizures (FS) occur at a significant rate in adult populations but it is not known whether the underlying mechanism or aetiological models are similar to patients with FS alone. We conducted a systematic review of patients with dual diagnosis to understand more about underlying mechanisms and natural history, in comparison to patients with FS only.

Methods The search strategy used the PRESS (Peer Review of Electronic Search Strategies) 2015 evidence-based checklist. We selected papers from MEDLINE, APA PsychInfo, and Google Scholar with search terms to identify primary research, on comorbid epilepsy and functional seizures confirmed by video EEG/telemetry, excluding people younger than 18 or over 75, and not including studies on populations with learning difficulties. Papers from the last 30 years were examined. Case reports were excluded. Papers were summarised by two authors and results corroborated.

Results 116 papers (with 1854 participants) were included. Studies indicated patients with DD and FS were similar in the pre-ictal changes to heart-rate variability. Both showed similar degrees of suggestibility and similar semiology. Both had similar levels of, and features of, dissociation during FS. Studies identified differences in the psychiatric profile between these groups, and of symptom burden and comorbidities, especially somatovisceral disorders (e.g. irritable bowel, headache, gastro-oesophageal reflux, or pain) which were more common in patients with FS than patients with DD.

Discussion/Conclusion Bayesian models of perception have been explored in functional conditions (Edwards, 2012),1 suggesting functional symptoms emerge due to a disorder of bodily priors. Recent work on interoception seeks to characterise the contribution of these bodily afferent signals and explore a role of dysregulation in aetiology of FS and functional conditions in general.

Our findings suggest that, in the lead up to and during events, patients with DD and FS both experience disordered interoception as indexed by the development of subjective bodily symptoms, and objective changes in autonomic tone (changes in heart-rate variability). Interictally, however, patients with a dual diagnosis are less likely to report other generalised functional symptoms, compared to those with FS alone. Our findings suggest potentially different underlying mechanisms within a Bayesian framework. In patients with FS alone there may be a generalised disorder of hyper-precise bodily priors, while in DD patients the primary problem may be one of excessive attention to bottom-up bodily afferent signals and phenomena linked to their epilepsy.


  1. Mark J Edwards, Rick A Adams, Harriet Brown, Isabel Pareés, Karl J Friston. A Bayesian account of ‘hysteria’, Brain 2012;135(11): 3495–3512,

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