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12-08-2013 | Mental health | Article

Cognitive impairment in schizophrenia a global problem


Free abstract

medwireNews: Cognitive impairment in patients with schizophrenia is still as substantial and generalized in its effects as it has ever been, despite improvements in how it is diagnosed and assessed, a review of the literature suggests.

“The current analysis updates the evidence of broad cognitive impairment in schizophrenia, again revealing moderate to severe impairment in people with schizophrenia relative to controls across all neuropsychological measures studied,” says the team, led by Dwight Dickinson (National Institute of Mental Health, Bethesda, Maryland, USA).

“Remarkably, despite significant changes in diagnostic criteria, assessment materials and practice, and sample ascertainment, the observed variation in the overall, grand mean effect size of cognitive impairment in schizophrenia over three decades of research is about 0.1 standard deviations, less than 10% of the total impairment observed.”

Dickinson and colleagues also note in Schizophrenia Research that global cognitive impairment in schizophrenia is consistent across different regions of the world, with linguistic and cultural differences having little effect. They suggest that “this impairment is probably the end-product of years of compromised neurodevelopment.”

A total of 100 studies using contemporary neuropsychological tests to measure cognitive performance in patients with schizophrenia were identified from a review of studies published between 2006 and 2012. These provided data on 9048 patients with schizophrenia and 8814 mentally healthy individuals for meta-analysis. The mean age of the patients was 35.1 years, and around 67% were male.

The researchers found that the schizophrenia patients performed significantly worse across 46 individual cognitive variables than mentally healthy individuals.

The effect sizes indicated that this impairment was moderate to severe across all the variables studied, and was greatest in the domains of processing speed and episodic memory.

There was also no evidence of geographic variation in the pattern of cognitive impairment, the researchers point out, with the overall effect size and those of individual items “strikingly consistent” across studies from Asia, Europe, and North America. This was despite “substantial geographic, cultural, and linguistic differences across groups,” they add.

And while newer investigative methods are testing whether this broad impairment can be divided into separate components, the researchers maintain that “the evidence for generalized cognitive impairment in schizophrenia… has reached the point of being overwhelming.”

They conclude: “Generalized cognitive impairment may present an unwieldy target for study, but it remains the clearest cognitive signal in schizophrenia research and a fundamental challenge for investigators trying to understand and treat this illness.”

medwireNews ( is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013

By Lucy Piper, Senior medwireNews Reporter

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