The dimensions of clinical and cognitive change in schizophrenia: evidence for independence of improvements
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- Harvey, P.D., Green, M.F., Bowie, C. et al. Psychopharmacology (2006) 187: 356. doi:10.1007/s00213-006-0432-1
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As cognitive impairments are related to deficits in everyday functioning in schizophrenia, treatment of these impairments may have the potential to reduce these functional deficits. To determine if treatments truly reduce cognitive impairment, it is important to discriminate direct cognitive effects of treatment from generalized treatment benefits on the multiple clinical dimensions of schizophrenia. Thus, this study used a database from an existing clinical trial and examined the relationships between changes in clinical symptoms and cognitive deficits with several different strategies.
Materials and methods
Two hundred and seventy stable but symptomatic outpatients with schizophrenia entered a study where they were switched from previous treatment to open-label ziprasidone. The present data are from the 6-month endpoint (n=184). Patients were examined at baseline and the 6-month endpoint with ratings of clinical symptoms based on the Positive and Negative Syndrome Scale (PANSS) and a neuropsychological (NP) assessment battery including aspects of cognitive functioning known to be related to functional outcome in schizophrenia.
Changes on the individual PANSS items and NP test scores were examined with two separate principal components analyses, revealing four dimensions of clinical change (psychosis, negative symptoms, affective symptoms, and agitation) and two dimensions of NP improvement. Pearson correlations between changes in the (1) factors derived from the analyses, (2) individual NP items based the four clinical dimensions of change, and (3) the 30 PANSS items and the two NP dimensions of change suggested minimal relationships (largest r=0.15).
This sample was selected because previous findings suggested that clinical and NP symptoms of schizophrenia significantly improved from baseline after a switch to ziprasidone treatment. While four dimensions of change in clinical symptoms and two dimensions of cognitive improvements were identified, clinical changes, regardless of how they were defined, were not related to NP improvements.