Functional seizures: Scoping review of classifications and proposal of novel three-axis model

Functional seizures (FS), psychogenic non-epileptic, or dissociative seizures, are paroxysmal events characterized by sudden changes in movement, sensory perception, behaviour, or responsiveness. Over the last three decades, there have been proposals to classify FS semiology, but no definitive classification exists. An overview of available literature on classification schemes for FS is relevant and might serve as a starting point for developing a globally accepted classification of FS. In this scoping review, we aim to: 1. Identify available literature on proposed classifications of FS, 2. Clarify the concepts of the different classification schemes with their essential elements, 3. Discern commonalities between the different classifications. MEDLINE and Embase databases were systematically searched until 14-06-2023, using synonyms for FS, semiology, and classification, and articles describing FS semiology classifications were included. We included 38 studies out of 593 screened abstracts. We tried to map all classification terms on a two-dimensional plane of movement versus responsiveness. We found several classes to be consistently present: 1. Nonmotor, normal responsiveness; 2. Nonmotor, impaired responsiveness 3. Minor motor, variable responsiveness; 4. Hypermotor, impaired responsiveness. Some classification terms could not be mapped as additional core characteristics of the semiology on the two-dimensional plane due to timing and ictal evolution. Current FS semiology classifications partially are aligned along the motor and responsiveness axes. Our review synthesizes timing and evolution as additional class to fully characterize semiology of individual FS. We propose a novel three-dimensional model to describe individual FS semiology, including time on a third axis.