Seizure duration in functional/dissociative seizures: measurement, variability and diagnostic significance

Seizure duration is widely regarded as a useful clinical feature in distinguishing functional/dissociative seizures (FDS) from epileptic seizures (ES), and prolonged events are often considered suggestive of FDS in clinical practice. However, reported durations vary substantially across studies and are strongly influenced by how seizure onset and offset are defined and measured. We conducted a structured MEDLINE search, supplemented by citation tracking, to identify studies reporting quantitative duration data in FDS derived from self- or witness-report, medical charts, or video-EEG (vEEG) monitoring. Forty-five studies were included. Reported FDS durations ranged from seconds to several hours. Duration estimates differed systematically according to measurement source: self- and witness-reported durations were generally longer and more variable than vEEG-measured events. Objectively timed FDS events tended to be longer than epileptic seizures, and thresholds such as ≥2 or ≥5 min increased the probability of FDS. However, no single duration cut-off reliably distinguished FDS from ES. A minority of FDS events were brief, suggesting potential diagnostic pitfalls. Prolonged or recurrent "status-like" functional events were frequently associated with emergency treatment and potential iatrogenic risk. Seizure duration in FDS is highly variable and method-dependent. Although prolonged events increase the likelihood of FDS, duration alone has limited diagnostic specificity and must be interpreted within clinical context. Standardised definitions of seizure onset and offset and transparent reporting of measurement source are needed to enhance diagnostic utility.