medwireNews: Findings from a meta-analysis and systematic review refute the common view of clinicians that cognitive deficits worsen during the early stages of psychosis.
The results therefore support a neurodevelopmental model for schizophrenia, rather than neuroprogressive or staging models, say researchers Emre Bora (University of Melbourne and Melbourne Health, Victoria, Australia) and Robin Murray (Institute of Psychiatry, London, UK).
The researchers conducted a meta-analysis of 25 studies published between 1987 and 2013 including 905 patients with first-episode psychosis (FEP), 560 patients at ultra-high risk (UHR) for psychosis, and 405 mentally healthy individuals.
The results show that for all three groups, cognitive performances, both globally and for cognitive domains, significantly improved over time.
"Studies of FEP samples clearly showed no decline within 5 years after the onset of psychosis," the researchers note in Schizophrenia Bulletin.
"FEP studies not included in this meta-analysis have shown similar findings, including samples followed for 10 years."
Even when analyses were restricted to only patients with first-episode schizophrenia, the results remained the same, "suggesting that cognitive trajectories of different diagnoses within FEP are likely to be similar," they point out.
"Together with the data in established schizophrenia, these findings suggest that there is no evidence of the loss of acquired cognitive skills after the onset of psychosis," Bora and Murray remark.
They found that the most consistent cognitive improvements in FEP patients occurred on tasks with significant practice effects, such as the Wisconsin Card Sorting Test and memory tasks. Improvements were less consistent for tasks with poor practice effects, such as letter fluency.
Reduction in symptoms, particularly negative symptoms, also contributed to improvements in working memory and executive functions, while a reduction in positive symptoms was associated with improvements in visual memory.
The findings were similar for UHR patients and there was no significant difference in cognitive changes between UHR patients who did and did not transfer to psychosis during follow up.
Antipsychotic medication may be one factor explaining improvements in cognitive function, but the researchers found no overall difference in cognitive changes between FEP patients who were antipsychotic naïve at baseline and those receiving treatment.
Given their findings, Bora and Murray conclude: "It is likely that cognitive abnormalities in schizophrenia develop long before the onset of the FEP as a result of abnormalities in neurodevelopment."
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