The latest edition of the International Classification of Diseases (ICD-10)1 defines dissociation as “ . . . a partial or complete loss of the normal integration between memories of the past, awareness of identity and immediate sensations, and control of body movements” (p 151). Thus defined, the concept of dissociation captures a heterogeneous group of psychiatric conditions previously subsumed within the broader construct of hysteria. Thedissociative (conversion) disorders category in ICD-10 comprises subcategories of dissociative amnesia, dissociative fugue, trance and possession disorders, dissociative anaesthesia and sensory loss, dissociative motor disorders and dissociative convulsions, and waste basket categories included to capture uncommon, impure, or less severe instances of dissociation. Other symptoms previously viewed as hysterical are placed within thesomatoform disorders category of ICD-10, on the grounds that their primary characteristic is an apparent disturbance of bodily rather than cerebral function. By contrast, DSM-IV2 classifies convulsions, motor dysfunction, and sensory loss as somatoform disorders, despite adopting an otherwise similar definition of dissociation and categorisation of dissociative complaints. In the context of this editorial we embrace the more inclusive scheme offered by ICD-10.

The basis for their inclusion within current psychiatric nosology is the assumption that dissociative disorders are primarily psychological in nature.1 Nevertheless, the concept of dissociation has important implications for practice and research within the neurological sphere also. Dissociative psychopathology was witnessed almost exclusively within the neurological setting until the late 19th and early 20th centuries, and many such patients present to neurologists even now. What is striking about dissociative symptoms is their apparent similarity to those found in many common neurological conditions, and it is often extremely difficult to distinguish between the two; the case of dissociative convulsions provides an instructive example.