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The two international systems of diagnostic classification for psychiatric disorders, ICD-10 and DSM-IV, differentiate a variety of disorders or syndromes characterized by the common feature of the presence of physical symptoms without "organic correlate." Conversion disorders (DSM) or dissociative disorders (ICD) are historically related to the concept of hysteria. Like psychoanalytical theories, the DSM and ICD refer to a psychological conflict preceding the onset of physical symptoms, although in a purely descriptive manner. The etiology of these disorders is still not very well understood. This article summarizes present knowledge from clinical and epidemiological studies. Functional neuroimaging studies on conversion disorders, although still very rare, allow testing of hypotheses about neuronal mechanisms. Such studies question the traditional and often misinterpreted dichotomy between organic and psychogenic diseases.

Patients with "functional" neurological diseases, i.e. suffering from nonorganic pseudo-neurological disorders, are common in neurological practice and account for a significant minority of neurological admissions. The nomenclature of these disorders is confusing and there is still no satisfactory system of classification. Many of these patients are misdiagnosed. The diagnostic problems and treatment of these disorders are illustrated by 4 case reports. Pathophysiologically the disorders are ill understood. Many of their bizarre features may serve as a means of nonverbal communication for these patients. Their management requires close collaboration between neurologists and psychiatrists. Behavioural therapy may be a more appropriate treatment for these disorders than classical analytic psychotherapy.