Approaches to an exact definition of schizo-affective psychoses for research purposes.

The perplexity psychiatry is faced with when approaching the problem of 'schizo-affective disorders' is the result of two characteristic features of human psychology: The first consists in the tendency to pick up quickly attractively formulated terms and to prefer them to others designating the same facts. The second psychological trend referred to concerns the use of a well-sounding term in a definition which deviates from the original one. The nosological implications of the existence of the 'cases in between' (K. Schneider), attributable neither to schizophrenia nor to cyclothymia, are briefly reviewed. It is suggested to speak of schizo-affective disorders only if the criteria for both disorders manifest simultaneously. Applying the Vienna Research Criteria we found that 'schizo-affective' disorders occur rarely as compared to other frequently used less restrictive diagnostic instruments.