Measuring What Matters in Functional/Dissociative Seizures: Frequency Correlates and Development of a Patient-Reported Severity Scale

Section One: Literature Review
Factors Related to Functional/Dissociative Seizure Frequency: A Systematic Review

Objectives: Seizure frequency is commonly used as a primary outcome and proxy for severity in functional/dissociative seizures (FDS), despite concerns about its validity and reliability. This systematic review aimed to (1) identify correlates of FDS frequency, and (2) consider the extent to which FDS counts capture seizure burden in the context of an ongoing project developing an FDS-specific severity PROM.
Methods: Following preregistration, PsycInfo, MEDLINE, CINAHL and Cochrane Reviews were searched using terms covering diagnosis, severity/frequency, and correlates. This was an update of an existing review which excluded FDS frequency findings, instead reported here. Eligible studies reported correlational data between FDS frequency and any variable in adults. A narrative review organised by conceptual domain was developed.
Results: Eighteen studies involving 848 people with FDS were reviewed. Health-related quality of life and functioning were impaired, but associations with seizure frequency were inconsistent. Variables related to distress were elevated yet showed weak or non-significant correlations with frequency. Stronger relationships were observed for specific processes (avoidance, self-esteem, coping, hyperventilation). Demographic and clinical variables showed little association with frequency.
Conclusions: There is great variability in the measurement of FDS frequency, and it appears to represent only one facet of FDS burden to be incorporated as one component of multidimensional FDS severity outcome measurement.

Section Two: Empirical Study
Development and Initial Validation of a Self-report Seizure Severity Measure for Individuals Experiencing Functional/Dissociative Seizures

Objectives: To develop and provide initial validation of the Functional/Dissociative Seizure Severity Scale (FDSS), a measure of functional/dissociative seizure (FDS) severity.
Design: Cross-sectional psychometric study.
Methods: 135 adults with FDS were recruited online and completed an FDSS item pool, measures of anxiety, depression, trauma, health-related quality of life (HRQoL) and somatic symptoms, and seizure frequency and duration indices. Exploratory factor analysis (EFA) and Rasch modelling informed item reduction, dimensionality and scale functioning. Internal consistency, test–retest reliability and convergent validity were examined.
Results: EFA yielded a 19-item, five-factor solution. Internal consistency was high for the total scale and acceptable for subscales. Test–retest reliability for the total score was good. Scores showed moderate to strong associations with HRQoL and somatic symptoms, and smaller correlations with anxiety, depression and post-traumatic stress. Associations with seizure frequency were modest and largely confined to physical manifestations. Rasch analyses supported acceptable item fit and ordered categories but indicated suboptimal targeting at higher severity.
Conclusions: The FDSS shows promising reliability and validity, capturing FDS severity beyond seizure counts alone. Areas for item refinements have been identified allowing for the measure to be revised before future testing in longitudinal studies capable of investigating its ability to capture change.