Functional neurological symptoms occur commonly in healthy adults: implications for the pathophysiology of FND

ObjectivesFunctional neurological symptoms which do not meet clinical definitions of functional neurological disorder (FND) are common in clinical practice. Understanding the distinction between these benign functional symptoms and FND is crucial in defining FND as an entity for study, and as a clinical syndrome. We aimed to measure the frequency of functional symptoms in people who do not have FND. MethodsA survey was administered to 95 clinicians who attended an international conference on FND. Participants were asked to report the occurrence and characteristics of experiences with features of functional sensory or motor symptoms, or dissociation. ResultsOf the 95 people who responded to the survey, 57.4% reported having experienced any functional symptoms, and 47.9% reported having experienced functional motor or sensory symptoms. The symptoms reported were generally short-lived and caused only mild distress and disruption. Most respondents who reported having experienced a functional symptom reported having had multiple events through their lives. InterpretationThe results suggest that the lifetime occurrence of functional neurological symptoms is at least two orders of magnitude higher than the prevalence of FND. The high prevalence of functional symptoms in people who have never had FND challenges the common assumption that the occurrence of functional neurological symptoms is synonymous with FND. We propose that FND is better conceived of as a failure of the mechanisms by which functional neurological symptoms resolve, rather than the occurrence of functional symptoms per se. This reconceptualization implies new research directions for the underlying aetiology of FND.