Investigating the association between neurocognition and psychosis in bipolar disorder: further evidence for the overlap with schizophrenia.

OBJECTIVES: In schizophrenia, a distinction is made between psychosis with developmental and cognitive impairment on the one hand and psychosis without developmental impairment and positive symptoms on the other. In this study, we investigated whether this model can be extended to bipolar disorder by testing the hypothesis that neurocognitive functioning is inversely related to positive psychotic symptoms in bipolar disorder.
METHODS: Neurocognitive functioning and psychopathology were assessed in (i) 76 patients with bipolar disorder, (ii) 39 of their healthy first-degree relatives, and (iii) 61 healthy controls. Cognitive performance of bipolar patients and their first-degree relatives was investigated, taking into account the possible moderating effect of the level of expression of psychosis in patients and relatives.
RESULTS: Bipolar patients showed impaired cognitive performance on multiple cognitive domains, whereas performance of their relatives was comparable to that of controls. A history of psychotic symptoms in patients was suggestive of less likelihood of cognitive alterations in relatives, and the presence of subclinical psychotic symptoms within the group of relatives predicted better cognitive performance.
CONCLUSIONS: The finding of similar psychosis-cognition associations in bipolar disorder as implied by the two pathways leading to nonaffective psychotic disorders suggests that this model might be extended to the continuum spanning affective and nonaffective psychosis. This is in line with the idea of a partially overlapping vulnerability to bipolar disorder and schizophrenia and provides an explanation for the apparent differences in cognitive alterations in those at risk for the two disorders.