Aetiological Heterogeneity of Schizophrenia: The Problem and the Evidence

When Kraepelin formulated the concept of dementia praecox, he lumped together a number of diagnostic categories. One of his reasons for doing so was that he had seen many patients who ended up in the same kind of demented state, even though their initial symptoms might have been quite different. He noted that even some cases presenting with mania, or melancholia, took the same downhill course as did the more classic cases of dementia praecox. Kraepelin, aware of the striking paradigm of general paresis, stated that “a single morbid process” explained the downhill course (Kraepelin, 1983, p. 68).