Conversion disorder: understanding the pathogenic links between emotion and motor systems in the brain.

When neurology and psychiatry moved apart from each other around the turn of the 20th century, casualties included the many patients with unexplained neurological disorders. Many labels have been applied to these patients. Some are descriptive (functional disorders, medically unexplained symptoms), while others refer to a presumed aetiology (psychogenic, hysteria, non-organic) or putative mechanism (dissociative or conversion disorder). Whatever is the label, for some physicians these patients are among the most interesting and challenging in the clinic. For others they are frustrating, using much time and resources for an often disappointing outcome. Whether you are an enthusiast or nihilist, it is clear that that neither neurology nor psychiatry alone have succeeded in sufficiently advancing our neurobiological understanding or management of these disorders. The slow progress is in stark contrast to the scale of the problem. Medically unexplained neurological symptoms account for 30% of referred neurology outpatients (Carson et al., 2000; Stone et al., 2009). Conversion disorder alone, explicitly associated with psychological stressors at the outset, accounts for 5% of referrals and is a stable, accurate Psychogenic movement disorders are common in neurological practice, including tremor, dystonia, gait change and paralysis. Diagnostic criteria emphasize clinical observations such as inconsistency , distractibility and false neurological signs (Fahn and Williams, 1988). These can be both sensitive and specific, at least in the context of a movement disorder clinic (Shill and Gerber, 2006). Physiological criteria have also been developed, such as coherence of tremor oscillations distinguishing psychogenic from organic syndromes (McAuley and Rothwell, 2004). The emphasis in this 'neurological' approach is on the physical examination , supplemented by physiological tests. The psychological aspects of the disease take second place, e.g. requiring 'obvious' but not specified psychiatric or emotional disturbance (Fahn and Williams, 1988; Shill and Gerber, 2006). In contrast, the 'psychiatric' approach emphasizes features of the clinical interview, including psychological factors at outset and inferences of intent. This is not ideal as a diagnostic 'gold standard' for developing a biological science of conversion disorder but the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) at least provides strict diagnostic criteria. The diagnosis requires the temporal association of psychological factors with the neurological symptoms (Criterion B: note that in the current revision of DSM, the aetiological relevance of the psychological factors has been downgraded from causal to association only). A further condition (Criterion C) is the lack of wilful simulation of symptoms (otherwise indicative of …