Schizophrenia is classified as a psychotic disorder. Is it more of a cognitive disorder than one defined presently by presence of psychotic symptoms? Has emphasis on psychotic symptoms lead us to a blind alley? Was wrong focus the reason for lack of meaningful progress in treatment ever since the disease was described? Kahn and Keefe make a strong argument to reconsider schizophrenia as a primary cognitive disorder in this article.
Cognition in this article reflect any measure of cognitive performance such as memory, attention, acquisition of knowledge, processing speed, reasoning, and executive function.
They make five arguments in support of their idea
1.Poor cognition is a risk factor for schizophrenia. for example large Swedish study showed that children with the lowest grades had a 4-fold risk for developing schizophrenia. 2. Cognitive decline presents before the onset of psychosis. Individuals who later develop schizophrenia are more likely to show progressive lag or relative cognitive decline years prior to onset of illness 3. Cognitive decline continues after the onset of psychosis.cognitive performance is 1 to 2 standard deviations (SDs) lower than age-matched control subjects. 4. Poor premorbid cognitive decline show specificity ie cognitive dysfunction prior to psychosis onset may distinguish it from other psychiatric disorders. The evidence described suggest that mean cognitive underperformance during adolescence and at first presentation of psychosis differentiates schizophrenia from bipolar disorder. 5. Cognitive decline predicts the functional outcome.
Counter view: 1. MOST individuals with poor cognition will NOT develop schizophrenia. 2.Cognitive underperformace may not distinguish schizophrenia from bipolar disorder . In fact they may share many features including impaired cognition. 3. Distinction between schizophrenia as condition of cognitive decline and others ( bipolar/ other psychotic disorders) with normal cognition is less realistic. 4. Authors do not explore / offer explanation for recovery observed in schizophrenia.
In the accompanying editorial Stephen Heckers agree that cognitive underperformance deserves more attention in diagnostic assessments and treatment targets.The call to discard it as a psychotic disorder is described as premature.
Comment: It is possible that all symptoms of schizophrenia could be explained as failures of cognitive function, if we consider all thoughts and behaviour as expressions or experiences built fundamentally from simpler cognitive processes, which we may not have clearly understood or measured yet.
Summary of the article:
Schizophrenia is a cognitive illness: time for a change in focus. Kahn RS, Keefe RS.JAMA Psychiatry. 2013 Oct 1;70(10):1107-12