The contribution of psychiatric epidemiology Cultural influences on the psychoses

Epidemiologists have been keen to discover whether psychiatric conditions are universal and appear with the same incidence across human populations. Universality would minimize the role of culture in shaping the form of a condition, while a uniform incidence would indicate that biological factors played a major role in aetiology. Schizophrenia has been the focus of many epidemiological surveys, especially the cross-national studies conducted by the World Health Organization ( WHO). The International Pilot Study of Schizophrenia(4) showed that it was possible to conduct a psychiatric epidemiological study across a wide variety of cultures and languages.(5) The use of standardized assessment and diagnostic techniques revealed that the core symptoms of schizophrenia were subject to few cultural variations. The most striking difference in the form of the illness was that catatonic symptoms were relatively frequent in patients from developing countries, but rare in the other centres.

The success of this study led to an even more ambitious project—the Determinants of the Outcome of Severe Mental Disorders. The main aim was to collect epidemiologically based samples of psychotic patients making a first contact with health services in centres around the world. This was designed to allow the comparison of incidence rates, and subsequently of the outcome of patients in different cultures using relatively unbiased samples. It was found that the incidence of narrowly defined schizophrenia was remarkably uniform across a diversity of countries. (6) However, when patients with a broad diagnosis of schizophrenia but lacking the core Schneiderian symptoms were considered, the incidence rates across centres showed a threefold difference which was highly significant. This suggests that socio cultural factors are likely to play a much greater role in the aetiology of non-Schneiderian schizophrenia than in the narrowly defined form, although the nature of these factors remains to be determined.

Dramatic differences in outcome at a 2-year follow-up were found, with schizophrenic patients in developing centres faring considerably better than those in developed centres despite a paucity of psychiatric personnel and facilities. This was not explained by a higher proportion of cases with an acute onset in the developing centres, raising intriguing questions about the beneficial aspects of traditional cultures. Explanations that have been proposed include beliefs that the causes of illness are external to the patient, the low demands for productivity and punctuality in an agrarian economy, and the quality of traditional family life. Only the latter has been investigated, using the Expressed Emotion measure, and appears to make an important contribution since family carers in India are far less critical and more tolerant of patients with schizophrenia than their counterparts in Britain. (7)

Mania has been the focus of much less transcultural research than schizophrenia, but what little there is suggests that psychotic experiences are more common in Nigerian and African-Caribbean patients than in patients from European countries. (89)

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