Executive function in patients with remitted bipolar disorder and schizophrenia and its relationship with functional outcome

Abstract

Background: Recent studies have reported that differences in cognitive performance between schizophrenic and bipolar patients seem to be smaller than expected. Patients with schizophrenia have consistently shown frontal executive dysfunctions, but studies regarding executive abilities in bipolar patients are scarce and discrepant. As executive function has been associated with psychosocial functioning in schizophrenia, we wanted to investigate if such a relationship is also present in bipolar disorder and the differences between the two groups.

Methods: Executive function was assessed in 49 euthymic (at least 6 months in remission, Hamilton Depression Rating Scale < or = 8 and Young Mania Rating Scale < or = 6) bipolar and in 49 schizophrenic, residual-type (with at least 1 year without acute exacerbation and predominant negative symptomatology) patients, by the Wisconsin Card Sorting Test (WCST), FAS Test (COWAT) and Trail Making Test. Baseline clinical and psychosocial variables were controlled and psychopathology evaluated by means of the Positive and Negative Syndrome Scale (PANSS).

Results: The two groups showed a similar pattern of cognitive deficits in tests of executive function, except for the number of categories achieved in the WCST, which was significantly lower in the schizophrenic group (F = 7.26; p = 0.009). Functional outcome was predicted by the negative syndrome (PANSSN) and perseverative errors (WCST) in schizophrenic patients, and general psychopathology (PANSSG) was the best predictor of functional outcome in the bipolar group.

Conclusion: Executive function was a good predictor of functional outcome in the schizophrenic group, whereas clinical variables were more predictive of the bipolar one. Patterns of cognitive disturbances in tasks of executive function are similar in both groups but quantitatively more marked in schizophrenia.