Functional/dissociative seizures: Proposal for a new diagnostic label and definition by the ILAE task force

The acceptability and validity of the term "psychogenic nonepileptic seizures" (PNES) have been questioned. Currently, numerous alternative terms, such as "conversion," "dissociative," "functional," "attacks," and "events," are used in both medical literature and clinical practice, leading to confusion among professionals and patients. The lack of a uniform diagnostic label is likely to impede research funding and service development. The International League Against Epilepsy (ILAE) Psychiatry Commission charged its task force focusing on these seizures to propose a more uniform and integrative terminology. Members of the previous ILAE PNES Task Force (2017-2021) helped to organize two workshops to try to build a consensus for a new terminology. These meetings involved experts by experience, clinicians, and researchers, including representatives of the Functional Neurological Disorders Society (an international professional organization), FND Hope (an international patient advocacy organization), and the American Epilepsy Society. The current task force (2021-2025) continued this work by reviewing the existing literature and debating the nomenclature and classification of seizures commonly labeled as PNES. The present proposal paper synthesizes the findings of this process. Based on our critical consideration of the literature, academic insights, and clinical experience, and noting the current international medical and psychiatric classification systems, the ILAE task force proposes the new term "functional/dissociative seizures" (FDS). This proposal paper explores the pros and cons of each component of the label "functional," "dissociative," and "seizure" from different perspectives, taking account of patient and health care professional acceptability, diagnostic and semiological considerations, underlying illness mechanisms, treatment provision, and health-economic, sociocultural, and linguistic factors. The dual characterization and use of a slash offer clinicians flexibility to adopt either "functional" or "dissociative," or both, in their practice depending on the patient's profile, their own preferences, and the cultural/linguistic context. The abbreviation "FDS" is recommend for use in scientific writings.