Review article
Why Kraepelin was right: schizophrenia as a cognitive disorder

In this article, the arguments for a concept of schizophrenia formulated by Kraepelin as “dementia praecox” are presented. It is shown that, given the current state of knowledge, Kraepelin was right for several reasons. First, low intelligence is a risk factor for schizophrenia. Second, cognitive decline and intellectual underperformance precede the onset of psychosis by many years. Third, the decline in cognitive functioning continues after psychosis onset. Fourth, while cognitive underperformance prior to psychosis has not definitively been shown to be specific to schizophrenia, it does distinguish it from the ‘other’ major psychotic illness, bipolar disorder. Finally, cognitive underperformance is an important predictor of long-term clinical course and outcome in schizophrenia.

The consequences of considering schizophrenia as primarily a cognitive rather than a psychotic disorder are manifold. First, cognitive decline prior to onset of psychosis should be part of the diagnosis. Second, treatment of the cognitive deficits should be central to any therapeutic guidelines. Third, the whole concept of schizophrenia as an illness that presents with psychosis should be revised: it presents with cognitive decline. Fourth, the age of onset of the illness is probably a decade earlier than we now assume.